import warnings
import re
import csv
import mimetypes
import time

from werkzeug import secure_filename

from flask import (request, redirect, flash, abort, json, Response,
                   get_flashed_messages, stream_with_context)
from jinja2 import contextfunction
try:
    import tablib
except ImportError:
    tablib = None
from wtforms.fields import HiddenField
from wtforms.fields.core import UnboundField
from wtforms.validators import ValidationError, InputRequired

from flask_admin.babel import gettext

from flask_admin.base import BaseView, expose
from flask_admin.form import BaseForm, FormOpts, rules
from flask_admin.model import filters, typefmt
from flask_admin.actions import ActionsMixin
from flask_admin.helpers import (get_form_data, validate_form_on_submit,
                                 get_redirect_target, flash_errors)
from flask_admin.tools import rec_getattr
from flask_admin._backwards import ObsoleteAttr
from flask_admin._compat import (iteritems, itervalues, OrderedDict,
                                 as_unicode, csv_encode, text_type)
from .helpers import prettify_name, get_mdict_item_or_list
from .ajax import AjaxModelLoader

# Used to generate filter query string name
filter_char_re = re.compile('[^a-z0-9 ]')
filter_compact_re = re.compile(' +')


class ViewArgs(object):
    """
        List view arguments.
    """
    def __init__(self, page=None, sort=None, sort_desc=None, search=None, filters=None, extra_args=None):
        self.page = page
        self.sort = sort
        self.sort_desc = bool(sort_desc)
        self.search = search
        self.filters = filters

        if not self.search:
            self.search = None

        self.extra_args = extra_args or dict()

    def clone(self, **kwargs):
        if self.filters:
            flt = list(self.filters)
        else:
            flt = None

        kwargs.setdefault('page', self.page)
        kwargs.setdefault('sort', self.sort)
        kwargs.setdefault('sort_desc', self.sort_desc)
        kwargs.setdefault('search', self.search)
        kwargs.setdefault('filters', flt)
        kwargs.setdefault('extra_args', dict(self.extra_args))

        return ViewArgs(**kwargs)


class FilterGroup(object):
    def __init__(self, label):
        self.label = label
        self.filters = []

    def append(self, filter):
        self.filters.append(filter)

    def non_lazy(self):
        filters = []
        for item in self.filters:
            copy = dict(item)
            copy['operation'] = as_unicode(copy['operation'])
            options = copy['options']
            if options:
                copy['options'] = [(k, text_type(v)) for k, v in options]

            filters.append(copy)
        return as_unicode(self.label), filters

    def __iter__(self):
        return iter(self.filters)


class BaseModelView(BaseView, ActionsMixin):
    """
        Base model view.

        This view does not make any assumptions on how models are stored or managed, but expects the following:

            1. The provided model is an object
            2. The model contains properties
            3. Each model contains an attribute which uniquely identifies it (i.e. a primary key for a database model)
            4. It is possible to retrieve a list of sorted models with pagination applied from a data source
            5. You can get one model by its identifier from the data source

        Essentially, if you want to support a new data store, all you have to do is:

            1. Derive from the `BaseModelView` class
            2. Implement various data-related methods (`get_list`, `get_one`, `create_model`, etc)
            3. Implement automatic form generation from the model representation (`scaffold_form`)
    """
    # Permissions
    can_create = True
    """Is model creation allowed"""

    can_edit = True
    """Is model editing allowed"""

    can_delete = True
    """Is model deletion allowed"""

    can_view_details = False
    """
        Setting this to true will enable the details view. This is recommended
        when there are too many columns to display in the list_view.
    """

    can_export = False
    """Is model list export allowed"""

    # Templates
    list_template = 'admin/model/list.html'
    """Default list view template"""

    edit_template = 'admin/model/edit.html'
    """Default edit template"""

    create_template = 'admin/model/create.html'
    """Default create template"""

    details_template = 'admin/model/details.html'
    """Default details view template"""

    # Modal Templates
    edit_modal_template = 'admin/model/modals/edit.html'
    """Default edit modal template"""

    create_modal_template = 'admin/model/modals/create.html'
    """Default create modal template"""

    details_modal_template = 'admin/model/modals/details.html'
    """Default details modal view template"""

    # Modals
    edit_modal = False
    """Setting this to true will display the edit_view as a modal dialog."""

    create_modal = False
    """Setting this to true will display the create_view as a modal dialog."""

    details_modal = False
    """Setting this to true will display the details_view as a modal dialog."""

    # Customizations
    column_list = ObsoleteAttr('column_list', 'list_columns', None)
    """
        Collection of the model field names for the list view.
        If set to `None`, will get them from the model.

        For example::

            class MyModelView(BaseModelView):
                column_list = ('name', 'last_name', 'email')

        (Added in 1.4.0) SQLAlchemy model attributes can be used instead of strings::

            class MyModelView(BaseModelView):
                column_list = ('name', User.last_name)

        When using SQLAlchemy models, you can reference related columns like this::
            class MyModelView(BaseModelView):
                column_list = ('<relationship>.<related column name>',)
    """

    column_exclude_list = ObsoleteAttr('column_exclude_list',
                                       'excluded_list_columns', None)
    """
        Collection of excluded list column names.

        For example::

            class MyModelView(BaseModelView):
                column_exclude_list = ('last_name', 'email')
    """

    column_details_list = None
    """
        Collection of the field names included in the details view.
        If set to `None`, will get them from the model.
    """

    column_details_exclude_list = None
    """
        Collection of fields excluded from the details view.
    """

    column_export_list = None
    """
        Collection of the field names included in the export.
        If set to `None`, will get them from the model.
    """

    column_export_exclude_list = None
    """
        Collection of fields excluded from the export.
    """

    column_formatters = ObsoleteAttr('column_formatters', 'list_formatters', dict())
    """
        Dictionary of list view column formatters.

        For example, if you want to show price multiplied by
        two, you can do something like this::

            class MyModelView(BaseModelView):
                column_formatters = dict(price=lambda v, c, m, p: m.price*2)

        or using Jinja2 `macro` in template::

            from flask_admin.model.template import macro

            class MyModelView(BaseModelView):
                column_formatters = dict(price=macro('render_price'))

            # in template
            {% macro render_price(model, column) %}
                {{ model.price * 2 }}
            {% endmacro %}

        The Callback function has the prototype::

            def formatter(view, context, model, name):
                # `view` is current administrative view
                # `context` is instance of jinja2.runtime.Context
                # `model` is model instance
                # `name` is property name
                pass
    """

    column_formatters_export = None
    """
        Dictionary of list view column formatters to be used for export.

        Defaults to column_formatters when set to None.

        Functions the same way as column_formatters except
        that macros are not supported.
    """

    column_type_formatters = ObsoleteAttr('column_type_formatters', 'list_type_formatters', None)
    """
        Dictionary of value type formatters to be used in the list view.

        By default, three types are formatted:

        1. ``None`` will be displayed as an empty string
        2. ``bool`` will be displayed as a checkmark if it is ``True``
        3. ``list`` will be joined using ', '

        If you don't like the default behavior and don't want any type formatters
        applied, just override this property with an empty dictionary::

            class MyModelView(BaseModelView):
                column_type_formatters = dict()

        If you want to display `NULL` instead of an empty string, you can do
        something like this. Also comes with bonus `date` formatter::

            from datetime import date
            from flask_admin.model import typefmt

            def date_format(view, value):
                return value.strftime('%d.%m.%Y')

            MY_DEFAULT_FORMATTERS = dict(typefmt.BASE_FORMATTERS)
            MY_DEFAULT_FORMATTERS.update({
                    type(None): typefmt.null_formatter,
                    date: date_format
                })

            class MyModelView(BaseModelView):
                column_type_formatters = MY_DEFAULT_FORMATTERS

        Type formatters have lower priority than list column formatters.

        The callback function has following prototype::

            def type_formatter(view, value):
                # `view` is current administrative view
                # `value` value to format
                pass
    """

    column_type_formatters_export = None
    """
        Dictionary of value type formatters to be used in the export.

        By default, two types are formatted:

        1. ``None`` will be displayed as an empty string
        2. ``list`` will be joined using ', '

        Functions the same way as column_type_formatters.
    """

    column_labels = ObsoleteAttr('column_labels', 'rename_columns', None)
    """
        Dictionary where key is column name and value is string to display.

        For example::

            class MyModelView(BaseModelView):
                column_labels = dict(name='Name', last_name='Last Name')
    """

    column_descriptions = None
    """
        Dictionary where key is column name and
        value is description for `list view` column or add/edit form field.

        For example::

            class MyModelView(BaseModelView):
                column_descriptions = dict(
                    full_name='First and Last name'
                )
    """

    column_sortable_list = ObsoleteAttr('column_sortable_list',
                                        'sortable_columns',
                                        None)
    """
        Collection of the sortable columns for the list view.
        If set to `None`, will get them from the model.

        For example::

            class MyModelView(BaseModelView):
                column_sortable_list = ('name', 'last_name')

        If you want to explicitly specify field/column to be used while
        sorting, you can use a tuple::

            class MyModelView(BaseModelView):
                column_sortable_list = ('name', ('user', 'user.username'))

        When using SQLAlchemy models, model attributes can be used instead
        of strings::

            class MyModelView(BaseModelView):
                column_sortable_list = ('name', ('user', User.username))
    """

    column_default_sort = None
    """
        Default sort column if no sorting is applied.

        Example::

            class MyModelView(BaseModelView):
                column_default_sort = 'user'

        You can use tuple to control ascending descending order. In following example, items
        will be sorted in descending order::

            class MyModelView(BaseModelView):
                column_default_sort = ('user', True)
    """

    column_searchable_list = ObsoleteAttr('column_searchable_list',
                                          'searchable_columns',
                                          None)
    """
        A collection of the searchable columns. It is assumed that only
        text-only fields are searchable, but it is up to the model
        implementation to decide.

        Example::

            class MyModelView(BaseModelView):
                column_searchable_list = ('name', 'email')
    """

    column_editable_list = None
    """
        Collection of the columns which can be edited from the list view.

        For example::

            class MyModelView(BaseModelView):
                column_editable_list = ('name', 'last_name')
    """

    column_choices = None
    """
        Map choices to columns in list view

        Example::

            class MyModelView(BaseModelView):
                column_choices = {
                    'my_column': [
                        ('db_value', 'display_value'),
                    ]
                }
    """

    column_filters = None
    """
        Collection of the column filters.

        Can contain either field names or instances of :class:`~flask_admin.model.filters.BaseFilter` classes.

        Example::

            class MyModelView(BaseModelView):
                column_filters = ('user', 'email')
    """

    named_filter_urls = False
    """
        Set to True to use human-readable names for filters in URL parameters.

        False by default so as to be robust across translations.

        Changing this parameter will break any existing URLs that have filters.
    """

    column_display_pk = ObsoleteAttr('column_display_pk',
                                     'list_display_pk',
                                     False)
    """
        Controls if the primary key should be displayed in the list view.
    """

    column_display_actions = True
    """
        Controls the display of the row actions (edit, delete, details, etc.)
        column in the list view.

        Useful for preventing a blank column from displaying if your view does
        not use any build-in or custom row actions.

        This column is not hidden automatically due to backwards compatibility.

        Note: This only affects display and does not control whether the row
        actions endpoints are accessible.
    """

    simple_list_pager = False
    """
        Enable or disable simple list pager.
        If enabled, model interface would not run count query and will only show prev/next pager buttons.
    """

    form = None
    """
        Form class. Override if you want to use custom form for your model.
        Will completely disable form scaffolding functionality.

        For example::

            class MyForm(Form):
                name = StringField('Name')

            class MyModelView(BaseModelView):
                form = MyForm
    """

    form_base_class = BaseForm
    """
        Base form class. Will be used by form scaffolding function when creating model form.

        Useful if you want to have custom contructor or override some fields.

        Example::

            class MyBaseForm(Form):
                def do_something(self):
                    pass

            class MyModelView(BaseModelView):
                form_base_class = MyBaseForm

    """

    form_args = None
    """
        Dictionary of form field arguments. Refer to WTForms documentation for
        list of possible options.

        Example::

            from wtforms.validators import DataRequired
            class MyModelView(BaseModelView):
                form_args = dict(
                    name=dict(label='First Name', validators=[DataRequired()])
                )
    """

    form_columns = None
    """
        Collection of the model field names for the form. If set to `None` will
        get them from the model.

        Example::

            class MyModelView(BaseModelView):
                form_columns = ('name', 'email')

        (Added in 1.4.0) SQLAlchemy model attributes can be used instead of
        strings::

            class MyModelView(BaseModelView):
                form_columns = ('name', User.last_name)

        SQLA Note: Model attributes must be on the same model as your ModelView
        or you will need to use `inline_models`.
    """

    form_excluded_columns = ObsoleteAttr('form_excluded_columns',
                                         'excluded_form_columns',
                                         None)
    """
        Collection of excluded form field names.

        For example::

            class MyModelView(BaseModelView):
                form_excluded_columns = ('last_name', 'email')
    """

    form_overrides = None
    """
        Dictionary of form column overrides.

        Example::

            class MyModelView(BaseModelView):
                form_overrides = dict(name=wtf.FileField)
    """

    form_widget_args = None
    """
        Dictionary of form widget rendering arguments.
        Use this to customize how widget is rendered without using custom template.

        Example::

            class MyModelView(BaseModelView):
                form_widget_args = {
                    'description': {
                        'rows': 10,
                        'style': 'color: black'
                    }
                }

        Changing the format of a DateTimeField will require changes to both form_widget_args and form_args.

        Example::

            form_args = dict(
                start=dict(format='%Y-%m-%d %I:%M %p') # changes how the input is parsed by strptime (12 hour time)
            )
            form_widget_args = dict(
                start={'data-date-format': u'yyyy-mm-dd HH:ii P', 'data-show-meridian': 'True'} # changes how the DateTimeField displays the time
            )
    """

    form_extra_fields = None
    """
        Dictionary of additional fields.

        Example::

            class MyModelView(BaseModelView):
                form_extra_fields = {
                    'password': PasswordField('Password')
                }

        You can control order of form fields using ``form_columns`` property. For example::

            class MyModelView(BaseModelView):
                form_columns = ('name', 'email', 'password', 'secret')

                form_extra_fields = {
                    'password': PasswordField('Password')
                }

        In this case, password field will be put between email and secret fields that are autogenerated.
    """

    form_ajax_refs = None
    """
        Use AJAX for foreign key model loading.

        Should contain dictionary, where key is field name and value is either a dictionary which
        configures AJAX lookups or backend-specific `AjaxModelLoader` class instance.

        For example, it can look like::

            class MyModelView(BaseModelView):
                form_ajax_refs = {
                    'user': {
                        'fields': ('first_name', 'last_name', 'email'),
                        'page_size': 10
                    }
                }

        Or with SQLAlchemy backend like this::

            class MyModelView(BaseModelView):
                form_ajax_refs = {
                    'user': QueryAjaxModelLoader('user', db.session, User, fields=['email'], page_size=10)
                }

        If you need custom loading functionality, you can implement your custom loading behavior
        in your `AjaxModelLoader` class.
    """

    form_rules = None
    """
        List of rendering rules for model creation form.

        This property changed default form rendering behavior and makes possible to rearrange order
        of rendered fields, add some text between fields, group them, etc. If not set, will use
        default Flask-Admin form rendering logic.

        Here's simple example which illustrates how to use::

            from flask_admin.form import rules

            class MyModelView(ModelView):
                form_rules = [
                    # Define field set with header text and four fields
                    rules.FieldSet(('first_name', 'last_name', 'email', 'phone'), 'User'),
                    # ... and it is just shortcut for:
                    rules.Header('User'),
                    rules.Field('first_name'),
                    rules.Field('last_name'),
                    # ...
                    # It is possible to create custom rule blocks:
                    MyBlock('Hello World'),
                    # It is possible to call macros from current context
                    rules.Macro('my_macro', foobar='baz')
                ]
    """

    form_edit_rules = None
    """
        Customized rules for the edit form. Override `form_rules` if present.
    """

    form_create_rules = None
    """
        Customized rules for the create form. Override `form_rules` if present.
    """

    # Actions
    action_disallowed_list = ObsoleteAttr('action_disallowed_list',
                                          'disallowed_actions',
                                          [])
    """
        Set of disallowed action names. For example, if you want to disable
        mass model deletion, do something like this:

            class MyModelView(BaseModelView):
                action_disallowed_list = ['delete']
    """

    # Export settings
    export_max_rows = 0
    """
        Maximum number of rows allowed for export.

        Unlimited by default. Uses `page_size` if set to `None`.
    """

    export_types = ['csv']
    """
        A list of available export filetypes. `csv` only is default, but any
        filetypes supported by tablib can be used.

        Check tablib for https://github.com/kennethreitz/tablib/bloab/master/README.rst
        for supported types.
    """

    # Various settings
    page_size = 20
    """
        Default page size for pagination.
    """

    def __init__(self, model,
                 name=None, category=None, endpoint=None, url=None, static_folder=None,
                 menu_class_name=None, menu_icon_type=None, menu_icon_value=None):
        """
            Constructor.

            :param model:
                Model class
            :param name:
                View name. If not provided, will use the model class name
            :param category:
                View category
            :param endpoint:
                Base endpoint. If not provided, will use the model name.
            :param url:
                Base URL. If not provided, will use endpoint as a URL.
            :param menu_class_name:
                Optional class name for the menu item.
            :param menu_icon_type:
                Optional icon. Possible icon types:

                 - `flask_admin.consts.ICON_TYPE_GLYPH` - Bootstrap glyph icon
                 - `flask_admin.consts.ICON_TYPE_FONT_AWESOME` - Font Awesome icon
                 - `flask_admin.consts.ICON_TYPE_IMAGE` - Image relative to Flask static directory
                 - `flask_admin.consts.ICON_TYPE_IMAGE_URL` - Image with full URL
            :param menu_icon_value:
                Icon glyph name or URL, depending on `menu_icon_type` setting
        """
        self.model = model

        # If name not provided, it is model name
        if name is None:
            name = '%s' % self._prettify_class_name(model.__name__)

        super(BaseModelView, self).__init__(name, category, endpoint, url, static_folder,
                                            menu_class_name=menu_class_name,
                                            menu_icon_type=menu_icon_type,
                                            menu_icon_value=menu_icon_value)

        # Actions
        self.init_actions()

        # Scaffolding
        self._refresh_cache()

    # Endpoint
    def _get_endpoint(self, endpoint):
        if endpoint:
            return super(BaseModelView, self)._get_endpoint(endpoint)

        return self.model.__name__.lower()

    # Caching
    def _refresh_forms_cache(self):
        # Forms
        self._form_ajax_refs = self._process_ajax_references()

        if self.form_widget_args is None:
            self.form_widget_args = {}

        self._create_form_class = self.get_create_form()
        self._edit_form_class = self.get_edit_form()
        self._delete_form_class = self.get_delete_form()

        # List View In-Line Editing
        if self.column_editable_list:
            self._list_form_class = self.get_list_form()
        else:
            self.column_editable_list = {}

    def _refresh_filters_cache(self):
        self._filters = self.get_filters()

        if self._filters:
            self._filter_groups = OrderedDict()
            self._filter_args = {}

            for i, flt in enumerate(self._filters):
                key = as_unicode(flt.name)
                if key not in self._filter_groups:
                    self._filter_groups[key] = FilterGroup(flt.name)
                self._filter_groups[key].append({
                    'index': i,
                    'arg': self.get_filter_arg(i, flt),
                    'operation': flt.operation(),
                    'options': flt.get_options(self) or None,
                    'type': flt.data_type
                })

                self._filter_args[self.get_filter_arg(i, flt)] = (i, flt)
        else:
            self._filter_groups = None
            self._filter_args = None

    def _refresh_form_rules_cache(self):
        if self.form_create_rules:
            self._form_create_rules = rules.RuleSet(self, self.form_create_rules)
        else:
            self._form_create_rules = None

        if self.form_edit_rules:
            self._form_edit_rules = rules.RuleSet(self, self.form_edit_rules)
        else:
            self._form_edit_rules = None

        if self.form_rules:
            form_rules = rules.RuleSet(self, self.form_rules)

            if not self._form_create_rules:
                self._form_create_rules = form_rules

            if not self._form_edit_rules:
                self._form_edit_rules = form_rules

    def _refresh_cache(self):
        """
            Refresh various cached variables.
        """
        # List view
        self._list_columns = self.get_list_columns()
        self._sortable_columns = self.get_sortable_columns()

        # Details view
        if self.can_view_details:
            self._details_columns = self.get_details_columns()

        # Export view
        if self.can_export:
            self._export_columns = self.get_export_columns()

        # Labels
        if self.column_labels is None:
            self.column_labels = {}

        # Forms
        self._refresh_forms_cache()

        # Search
        self._search_supported = self.init_search()

        # Choices
        if self.column_choices:
            self._column_choices_map = dict([
                (column, dict(choices))
                for column, choices in self.column_choices.items()
            ])
        else:
            self.column_choices = self._column_choices_map = dict()

        # Column formatters
        if self.column_formatters_export is None:
            self.column_formatters_export = self.column_formatters

        # Type formatters
        if self.column_type_formatters is None:
            self.column_type_formatters = dict(typefmt.BASE_FORMATTERS)

        if self.column_type_formatters_export is None:
            self.column_type_formatters_export = dict(typefmt.EXPORT_FORMATTERS)

        if self.column_descriptions is None:
            self.column_descriptions = dict()

        # Filters
        self._refresh_filters_cache()

        # Form rendering rules
        self._refresh_form_rules_cache()

        # Process form rules
        self._validate_form_class(self._form_edit_rules, self._edit_form_class)
        self._validate_form_class(self._form_create_rules, self._create_form_class)

    # Primary key
    def get_pk_value(self, model):
        """
            Return PK value from a model object.
        """
        raise NotImplementedError()

    # List view
    def scaffold_list_columns(self):
        """
            Return list of the model field names. Must be implemented in
            the child class.

            Expected return format is list of tuples with field name and
            display text. For example::

                ['name', 'first_name', 'last_name']
        """
        raise NotImplementedError('Please implement scaffold_list_columns method')

    def get_column_name(self, field):
        """
            Return a human-readable column name.

            :param field:
                Model field name.
        """
        if self.column_labels and field in self.column_labels:
            return self.column_labels[field]
        else:
            return self._prettify_name(field)

    def get_list_columns(self):
        """
            Returns a list of tuples with the model field name and formatted
            field name. If `column_list` was set, returns it. Otherwise calls
            `scaffold_list_columns` to generate the list from the model.
        """
        columns = self.column_list

        if columns is None:
            columns = self.scaffold_list_columns()

            # Filter excluded columns
            if self.column_exclude_list:
                columns = [c for c in columns if c not in self.column_exclude_list]

        return [(c, self.get_column_name(c)) for c in columns]

    def get_details_columns(self):
        """
            Returns a list of the model field names in the details view. If
            `column_details_list` was set, returns it. Otherwise calls
            `scaffold_list_columns` to generate the list from the model.
        """
        columns = self.column_details_list

        if columns is None:
            columns = self.scaffold_list_columns()

            # Filter excluded columns
            if self.column_details_exclude_list:
                columns = [c for c in columns
                           if c not in self.column_details_exclude_list]

        return [(c, self.get_column_name(c)) for c in columns]

    def get_export_columns(self):
        """
            Returns a list of the model field names in the export view. If
            `column_export_list` was set, returns it. Otherwise, if
            `column_list` was set, returns it. Otherwise calls
            `scaffold_list_columns` to generate the list from the model.
        """
        columns = self.column_export_list

        if columns is None:
            columns = self.column_list

            if columns is None:
                columns = self.scaffold_list_columns()

            # Filter excluded columns
            if self.column_export_exclude_list:
                columns = [c for c in columns
                           if c not in self.column_export_exclude_list]

        return [(c, self.get_column_name(c)) for c in columns]

    def scaffold_sortable_columns(self):
        """
            Returns dictionary of sortable columns. Must be implemented in
            the child class.

            Expected return format is a dictionary, where keys are field names and
            values are property names.
        """
        raise NotImplementedError('Please implement scaffold_sortable_columns method')

    def get_sortable_columns(self):
        """
            Returns a dictionary of the sortable columns. Key is a model
            field name and value is sort column (for example - attribute).

            If `column_sortable_list` is set, will use it. Otherwise, will call
            `scaffold_sortable_columns` to get them from the model.
        """
        if self.column_sortable_list is None:
            return self.scaffold_sortable_columns() or dict()
        else:
            result = dict()

            for c in self.column_sortable_list:
                if isinstance(c, tuple):
                    result[c[0]] = c[1]
                else:
                    result[c] = c

            return result

    def init_search(self):
        """
            Initialize search. If data provider does not support search,
            `init_search` will return `False`.
        """
        return False

    # Filter helpers
    def scaffold_filters(self, name):
        """
            Generate filter object for the given name

            :param name:
                Name of the field
        """
        return None

    def is_valid_filter(self, filter):
        """
            Verify that the provided filter object is valid.

            Override in model backend implementation to verify if
            the provided filter type is allowed.

            :param filter:
                Filter object to verify.
        """
        return isinstance(filter, filters.BaseFilter)

    def handle_filter(self, filter):
        """
            Postprocess (add joins, etc) for a filter.

            :param filter:
                Filter object to postprocess
        """
        return filter

    def get_filters(self):
        """
            Return a list of filter objects.

            If your model backend implementation does not support filters,
            override this method and return `None`.
        """
        if self.column_filters:
            collection = []

            for n in self.column_filters:
                if self.is_valid_filter(n):
                    collection.append(self.handle_filter(n))
                else:
                    flt = self.scaffold_filters(n)
                    if flt:
                        collection.extend(flt)
                    else:
                        raise Exception('Unsupported filter type %s' % n)
            return collection
        else:
            return None

    def get_filter_arg(self, index, flt):
        """
            Given a filter `flt`, return a unique name for that filter in
            this view.

            Does not include the `flt[n]_` portion of the filter name.

            :param index:
                Filter index in _filters array
            :param flt:
                Filter instance
        """
        if self.named_filter_urls:
            name = ('%s %s' % (flt.name, as_unicode(flt.operation()))).lower()
            name = filter_char_re.sub('', name)
            name = filter_compact_re.sub('_', name)
            return name
        else:
            return str(index)

    def _get_filter_groups(self):
        """
            Returns non-lazy version of filter strings
        """
        if self._filter_groups:
            results = OrderedDict()

            for group in itervalues(self._filter_groups):
                key, items = group.non_lazy()
                results[key] = items

            return results

        return None

    # Form helpers
    def scaffold_form(self):
        """
            Create `form.BaseForm` inherited class from the model. Must be
            implemented in the child class.
        """
        raise NotImplementedError('Please implement scaffold_form method')

    def scaffold_list_form(self, widget=None, validators=None):
        """
            Create form for the `index_view` using only the columns from
            `self.column_editable_list`.

            :param widget:
                WTForms widget class. Defaults to `XEditableWidget`.
            :param validators:
                `form_args` dict with only validators
                {'name': {'validators': [DataRequired()]}}

            Must be implemented in the child class.
        """
        raise NotImplementedError('Please implement scaffold_list_form method')

    def get_form(self):
        """
            Get form class.

            If ``self.form`` is set, will return it and will call
            ``self.scaffold_form`` otherwise.

            Override to implement customized behavior.
        """
        if self.form is not None:
            return self.form

        return self.scaffold_form()

    def get_list_form(self):
        """
            Get form class for the editable list view.

            Uses only validators from `form_args` to build the form class.

            Allows overriding the editable list view field/widget. For example::

                from flask_admin.model.widgets import XEditableWidget

                class CustomWidget(XEditableWidget):
                    def get_kwargs(self, subfield, kwargs):
                        if subfield.type == 'TextAreaField':
                            kwargs['data-type'] = 'textarea'
                            kwargs['data-rows'] = '20'
                        # elif: kwargs for other fields

                        return kwargs

                class MyModelView(BaseModelView):
                    def get_list_form(self):
                        return self.scaffold_list_form(widget=CustomWidget)
        """
        if self.form_args:
            # get only validators, other form_args can break FieldList wrapper
            validators = dict(
                (key, {'validators': value["validators"]})
                for key, value in iteritems(self.form_args)
                if value.get("validators")
            )
        else:
            validators = None

        return self.scaffold_list_form(validators=validators)

    def get_create_form(self):
        """
            Create form class for model creation view.

            Override to implement customized behavior.
        """
        return self.get_form()

    def get_edit_form(self):
        """
            Create form class for model editing view.

            Override to implement customized behavior.
        """
        return self.get_form()

    def get_delete_form(self):
        """
            Create form class for model delete view.

            Override to implement customized behavior.
        """
        class DeleteForm(self.form_base_class):
            id = HiddenField(validators=[InputRequired()])
            url = HiddenField()

        return DeleteForm

    def create_form(self, obj=None):
        """
            Instantiate model creation form and return it.

            Override to implement custom behavior.
        """
        return self._create_form_class(get_form_data(), obj=obj)

    def edit_form(self, obj=None):
        """
            Instantiate model editing form and return it.

            Override to implement custom behavior.
        """
        return self._edit_form_class(get_form_data(), obj=obj)

    def delete_form(self):
        """
            Instantiate model delete form and return it.

            Override to implement custom behavior.

            The delete form originally used a GET request, so delete_form
            accepts both GET and POST request for backwards compatibility.
        """
        if request.form:
            return self._delete_form_class(request.form)
        elif request.args:
            # allow request.args for backward compatibility
            return self._delete_form_class(request.args)
        else:
            return self._delete_form_class()

    def list_form(self, obj=None):
        """
            Instantiate model editing form for list view and return it.

            Override to implement custom behavior.
        """
        return self._list_form_class(get_form_data(), obj=obj)

    def validate_form(self, form):
        """
            Validate the form on submit.

            :param form:
                Form to validate
        """
        return validate_form_on_submit(form)

    def get_save_return_url(self, model, is_created=False):
        """
            Return url where user is redirected after successful form save.

            :param model:
                Saved object
            :param is_created:
                Whether new object was created or existing one was updated

            For example, redirect use to object details view after form save::

                class MyModelView(ModelView):
                    can_view_details = True

                    def get_save_return_url(self, model, is_created):
                        return self.get_url('.details_view', id=model.id)

        """
        return get_redirect_target() or self.get_url('.index_view')

    def _get_ruleset_missing_fields(self, ruleset, form):
        missing_fields = []

        if ruleset:
            visible_fields = ruleset.visible_fields
            for field in form:
                if field.name not in visible_fields:
                    missing_fields.append(field.name)

        return missing_fields

    def _show_missing_fields_warning(self, text):
        warnings.warn(text)

    def _validate_form_class(self, ruleset, form_class, remove_missing=True):
        form_fields = []
        for name, obj in iteritems(form_class.__dict__):
            if isinstance(obj, UnboundField):
                form_fields.append(name)

        missing_fields = []
        if ruleset:
            visible_fields = ruleset.visible_fields
            for field_name in form_fields:
                if field_name not in visible_fields:
                    missing_fields.append(field_name)

        if missing_fields:
            self._show_missing_fields_warning('Fields missing from ruleset: %s' % (','.join(missing_fields)))
        if remove_missing:
            self._remove_fields_from_form_class(missing_fields, form_class)

    def _validate_form_instance(self, ruleset, form, remove_missing=True):
        missing_fields = self._get_ruleset_missing_fields(ruleset=ruleset, form=form)
        if missing_fields:
            self._show_missing_fields_warning('Fields missing from ruleset: %s' % (','.join(missing_fields)))
        if remove_missing:
            self._remove_fields_from_form_instance(missing_fields, form)

    def _remove_fields_from_form_instance(self, field_names, form):
        for field_name in field_names:
            form.__delitem__(field_name)

    def _remove_fields_from_form_class(self, field_names, form_class):
        for field_name in field_names:
            delattr(form_class, field_name)

    # Helpers
    def is_sortable(self, name):
        """
            Verify if column is sortable.

            Not case-sensitive.

            :param name:
                Column name.
        """
        return name.lower() in (x.lower() for x in self._sortable_columns)

    def is_editable(self, name):
        """
            Verify if column is editable.

            :param name:
                Column name.
        """
        return name in self.column_editable_list

    def _get_column_by_idx(self, idx):
        """
            Return column index by
        """
        if idx is None or idx < 0 or idx >= len(self._list_columns):
            return None

        return self._list_columns[idx]

    def _get_default_order(self):
        """
            Return default sort order
        """
        if self.column_default_sort:
            if isinstance(self.column_default_sort, tuple):
                return self.column_default_sort
            else:
                return self.column_default_sort, False

        return None

    # Database-related API
    def get_list(self, page, sort_field, sort_desc, search, filters,
                 page_size=None):
        """
            Return a paginated and sorted list of models from the data source.

            Must be implemented in the child class.

            :param page:
                Page number, 0 based. Can be set to None if it is first page.
            :param sort_field:
                Sort column name or None.
            :param sort_desc:
                If set to True, sorting is in descending order.
            :param search:
                Search query
            :param filters:
                List of filter tuples. First value in a tuple is a search
                index, second value is a search value.
            :param page_size:
                Number of results. Defaults to ModelView's page_size. Can be
                overriden to change the page_size limit. Removing the page_size
                limit requires setting page_size to 0 or False.
        """
        raise NotImplementedError('Please implement get_list method')

    def get_one(self, id):
        """
            Return one model by its id.

            Must be implemented in the child class.

            :param id:
                Model id
        """
        raise NotImplementedError('Please implement get_one method')

    # Exception handler
    def handle_view_exception(self, exc):
        if isinstance(exc, ValidationError):
            flash(as_unicode(exc))
            return True

        if self._debug:
            raise

        return False

    # Model event handlers
    def on_model_change(self, form, model, is_created):
        """
            Perform some actions before a model is created or updated.

            Called from create_model and update_model in the same transaction
            (if it has any meaning for a store backend).

            By default does nothing.

            :param form:
                Form used to create/update model
            :param model:
                Model that will be created/updated
            :param is_created:
                Will be set to True if model was created and to False if edited
        """
        pass

    def _on_model_change(self, form, model, is_created):
        """
            Compatibility helper.
        """
        try:
            self.on_model_change(form, model, is_created)
        except TypeError:
            msg = ('%s.on_model_change() now accepts third ' +
                   'parameter is_created. Please update your code') % self.model
            warnings.warn(msg)

            self.on_model_change(form, model)

    def after_model_change(self, form, model, is_created):
        """
            Perform some actions after a model was created or updated and
            committed to the database.

            Called from create_model after successful database commit.

            By default does nothing.

            :param form:
                Form used to create/update model
            :param model:
                Model that was created/updated
            :param is_created:
                True if model was created, False if model was updated
        """
        pass

    def on_model_delete(self, model):
        """
            Perform some actions before a model is deleted.

            Called from delete_model in the same transaction
            (if it has any meaning for a store backend).

            By default do nothing.
        """
        pass

    def after_model_delete(self, model):
        """
            Perform some actions after a model was deleted and
            committed to the database.

            Called from delete_model after successful database commit
            (if it has any meaning for a store backend).

            By default does nothing.

            :param model:
                Model that was deleted
        """
        pass

    def on_form_prefill (self, form, id):
        """
            Perform additional actions to pre-fill the edit form.

            Called from edit_view, if the current action is rendering
            the form rather than receiving client side input, after
            default pre-filling has been performed.

            By default does nothing.

            You only need to override this if you have added custom
            fields that depend on the database contents in a way that
            Flask-admin can't figure out by itself. Fields that were
            added by name of a normal column or relationship should
            work out of the box.

            :param form:
                Form instance
            :param id:
                id of the object that is going to be edited
        """
        pass

    def create_model(self, form):
        """
            Create model from the form.

            Returns the model instance if operation succeeded.

            Must be implemented in the child class.

            :param form:
                Form instance
        """
        raise NotImplementedError()

    def update_model(self, form, model):
        """
            Update model from the form.

            Returns `True` if operation succeeded.

            Must be implemented in the child class.

            :param form:
                Form instance
            :param model:
                Model instance
        """
        raise NotImplementedError()

    def delete_model(self, model):
        """
            Delete model.

            Returns `True` if operation succeeded.

            Must be implemented in the child class.

            :param model:
                Model instance
        """
        raise NotImplementedError()

    # Various helpers
    def _prettify_name(self, name):
        """
            Prettify pythonic variable name.

            For example, 'hello_world' will be converted to 'Hello World'

            :param name:
                Name to prettify
        """
        return prettify_name(name)

    def get_empty_list_message(self):
        return gettext('There are no items in the table.')

    # URL generation helpers
    def _get_list_filter_args(self):
        if self._filters:
            filters = []

            for n in request.args:
                if not n.startswith('flt'):
                    continue

                if '_' not in n:
                    continue

                pos, key = n[3:].split('_', 1)

                if key in self._filter_args:
                    idx, flt = self._filter_args[key]

                    value = request.args[n]

                    if flt.validate(value):
                        filters.append((pos, (idx, as_unicode(flt.name), value)))
                    else:
                        flash(gettext('Invalid Filter Value: %(value)s', value=value))

            # Sort filters
            return [v[1] for v in sorted(filters, key=lambda n: n[0])]

        return None

    def _get_list_extra_args(self):
        """
            Return arguments from query string.
        """
        return ViewArgs(page=request.args.get('page', 0, type=int),
                        sort=request.args.get('sort', None, type=int),
                        sort_desc=request.args.get('desc', None, type=int),
                        search=request.args.get('search', None),
                        filters=self._get_list_filter_args())

    # URL generation helpers
    def _get_list_url(self, view_args):
        """
            Generate page URL with current page, sort column and
            other parameters.

            :param view:
                View name
            :param view_args:
                ViewArgs object with page number, filters, etc.
        """
        page = view_args.page or None
        desc = 1 if view_args.sort_desc else None

        kwargs = dict(page=page, sort=view_args.sort, desc=desc, search=view_args.search)
        kwargs.update(view_args.extra_args)

        if view_args.filters:
            for i, pair in enumerate(view_args.filters):
                idx, flt_name, value = pair

                key = 'flt%d_%s' % (i, self.get_filter_arg(idx, self._filters[idx]))
                kwargs[key] = value

        return self.get_url('.index_view', **kwargs)

    # Actions
    def is_action_allowed(self, name):
        """
            Override this method to allow or disallow actions based
            on some condition.

            The default implementation only checks if the particular action
            is not in `action_disallowed_list`.
        """
        return name not in self.action_disallowed_list

    def _get_field_value(self, model, name):
        """
            Get unformatted field value from the model
        """
        return rec_getattr(model, name)

    def _get_list_value(self, context, model, name, column_formatters,
                        column_type_formatters):
        """
            Returns the value to be displayed.

            :param context:
                :py:class:`jinja2.runtime.Context` if available
            :param model:
                Model instance
            :param name:
                Field name
            :param column_formatters:
                column_formatters to be used.
            :param column_type_formatters:
                column_type_formatters to be used.
        """
        column_fmt = column_formatters.get(name)
        if column_fmt is not None:
            value = column_fmt(self, context, model, name)
        else:
            value = self._get_field_value(model, name)

        choices_map = self._column_choices_map.get(name, {})
        if choices_map:
            return choices_map.get(value) or value

        type_fmt = None
        for typeobj, formatter in column_type_formatters.items():
            if isinstance(value, typeobj):
                type_fmt = formatter
                break
        if type_fmt is not None:
            value = type_fmt(self, value)

        return value

    @contextfunction
    def get_list_value(self, context, model, name):
        """
            Returns the value to be displayed in the list view

            :param context:
                :py:class:`jinja2.runtime.Context`
            :param model:
                Model instance
            :param name:
                Field name
        """
        return self._get_list_value(
            context,
            model,
            name,
            self.column_formatters,
            self.column_type_formatters,
        )

    def get_export_value(self, model, name):
        """
            Returns the value to be displayed in export.
            Allows export to use different (non HTML) formatters.

            :param model:
                Model instance
            :param name:
                Field name
        """
        return self._get_list_value(
            None,
            model,
            name,
            self.column_formatters_export,
            self.column_type_formatters_export,
        )

    def get_export_name(self, export_type='csv'):
        """
        :return: The exported csv file name.
        """
        filename = '%s_%s.%s' % (self.name,
                                 time.strftime("%Y-%m-%d_%H-%M-%S"),
                                 export_type)
        return filename

    # AJAX references
    def _process_ajax_references(self):
        """
            Process `form_ajax_refs` and generate model loaders that
            will be used by the `ajax_lookup` view.
        """
        result = {}

        if self.form_ajax_refs:
            for name, options in iteritems(self.form_ajax_refs):
                if isinstance(options, dict):
                    result[name] = self._create_ajax_loader(name, options)
                elif isinstance(options, AjaxModelLoader):
                    result[name] = options
                else:
                    raise ValueError('%s.form_ajax_refs can not handle %s types' % (self, type(options)))

        return result

    def _create_ajax_loader(self, name, options):
        """
            Model backend will override this to implement AJAX model loading.
        """
        raise NotImplementedError()

    # Views
    @expose('/')
    def index_view(self):
        """
            List view
        """
        if self.can_delete:
            delete_form = self.delete_form()
        else:
            delete_form = None

        # Grab parameters from URL
        view_args = self._get_list_extra_args()

        # Map column index to column name
        sort_column = self._get_column_by_idx(view_args.sort)
        if sort_column is not None:
            sort_column = sort_column[0]

        # Get count and data
        count, data = self.get_list(view_args.page, sort_column, view_args.sort_desc,
                                    view_args.search, view_args.filters)

        list_forms = {}
        if self.column_editable_list:
            for row in data:
                list_forms[self.get_pk_value(row)] = self.list_form(obj=row)

        # Calculate number of pages
        if count is not None:
            num_pages = count // self.page_size
            if count % self.page_size != 0:
                num_pages += 1
        else:
            num_pages = None

        # Various URL generation helpers
        def pager_url(p):
            # Do not add page number if it is first page
            if p == 0:
                p = None

            return self._get_list_url(view_args.clone(page=p))

        def sort_url(column, invert=False):
            desc = None

            if invert and not view_args.sort_desc:
                desc = 1

            return self._get_list_url(view_args.clone(sort=column, sort_desc=desc))

        # Actions
        actions, actions_confirmation = self.get_actions_list()

        clear_search_url = self._get_list_url(view_args.clone(page=0,
                                                              sort=view_args.sort,
                                                              sort_desc=view_args.sort_desc,
                                                              search=None,
                                                              filters=None))

        return self.render(
            self.list_template,
            data=data,
            list_forms=list_forms,
            delete_form=delete_form,

            # List
            list_columns=self._list_columns,
            sortable_columns=self._sortable_columns,
            editable_columns=self.column_editable_list,

            # Pagination
            count=count,
            pager_url=pager_url,
            num_pages=num_pages,
            page=view_args.page,
            page_size=self.page_size,

            # Sorting
            sort_column=view_args.sort,
            sort_desc=view_args.sort_desc,
            sort_url=sort_url,

            # Search
            search_supported=self._search_supported,
            clear_search_url=clear_search_url,
            search=view_args.search,

            # Filters
            filters=self._filters,
            filter_groups=self._get_filter_groups(),
            active_filters=view_args.filters,

            # Actions
            actions=actions,
            actions_confirmation=actions_confirmation,

            # Misc
            enumerate=enumerate,
            get_pk_value=self.get_pk_value,
            get_value=self.get_list_value,
            return_url=self._get_list_url(view_args),
        )

    @expose('/new/', methods=('GET', 'POST'))
    def create_view(self):
        """
            Create model view
        """
        return_url = get_redirect_target() or self.get_url('.index_view')

        if not self.can_create:
            return redirect(return_url)

        form = self.create_form()
        if not hasattr(form, '_validated_ruleset') or not form._validated_ruleset:
            self._validate_form_instance(ruleset=self._form_create_rules, form=form)

        if self.validate_form(form):
            # in versions 1.1.0 and before, this returns a boolean
            # in later versions, this is the model itself
            model = self.create_model(form)
            if model:
                flash(gettext('Record was successfully created.'))
                if '_add_another' in request.form:
                    return redirect(request.url)
                elif '_continue_editing' in request.form:
                    # if we have a valid model, try to go to the edit view
                    if model is not True:
                        url = self.get_url('.edit_view', id=self.get_pk_value(model), url=return_url)
                    else:
                        url = return_url
                    return redirect(url)
                else:
                    # save button
                    return redirect(self.get_save_return_url(model, is_created=True))

        form_opts = FormOpts(widget_args=self.form_widget_args,
                             form_rules=self._form_create_rules)

        if self.create_modal and request.args.get('modal'):
            template = self.create_modal_template
        else:
            template = self.create_template

        return self.render(template,
                           form=form,
                           form_opts=form_opts,
                           return_url=return_url)

    @expose('/edit/', methods=('GET', 'POST'))
    def edit_view(self):
        """
            Edit model view
        """
        return_url = get_redirect_target() or self.get_url('.index_view')

        if not self.can_edit:
            return redirect(return_url)

        id = get_mdict_item_or_list(request.args, 'id')
        if id is None:
            return redirect(return_url)

        model = self.get_one(id)

        if model is None:
            flash(gettext('Record does not exist.'))
            return redirect(return_url)

        form = self.edit_form(obj=model)
        if not hasattr(form, '_validated_ruleset') or not form._validated_ruleset:
            self._validate_form_instance(ruleset=self._form_edit_rules, form=form)

        if self.validate_form(form):
            if self.update_model(form, model):
                flash(gettext('Record was successfully saved.'))
                if '_add_another' in request.form:
                    return redirect(self.get_url('.create_view', url=return_url))
                elif '_continue_editing' in request.form:
                    return redirect(request.url)
                else:
                    # save button
                    return redirect(self.get_save_return_url(model, is_created=False))

        if request.method == 'GET':
            self.on_form_prefill(form, id)

        form_opts = FormOpts(widget_args=self.form_widget_args,
                             form_rules=self._form_edit_rules)

        if self.edit_modal and request.args.get('modal'):
            template = self.edit_modal_template
        else:
            template = self.edit_template

        return self.render(template,
                           model=model,
                           form=form,
                           form_opts=form_opts,
                           return_url=return_url)

    @expose('/details/')
    def details_view(self):
        """
            Details model view
        """
        return_url = get_redirect_target() or self.get_url('.index_view')

        if not self.can_view_details:
            return redirect(return_url)

        id = get_mdict_item_or_list(request.args, 'id')
        if id is None:
            return redirect(return_url)

        model = self.get_one(id)

        if model is None:
            flash(gettext('Record does not exist.'))
            return redirect(return_url)

        if self.details_modal and request.args.get('modal'):
            template = self.details_modal_template
        else:
            template = self.details_template

        return self.render(template,
                           model=model,
                           details_columns=self._details_columns,
                           get_value=self.get_list_value,
                           return_url=return_url)

    @expose('/delete/', methods=('POST',))
    def delete_view(self):
        """
            Delete model view. Only POST method is allowed.
        """
        return_url = get_redirect_target() or self.get_url('.index_view')

        if not self.can_delete:
            return redirect(return_url)

        form = self.delete_form()

        if self.validate_form(form):
             # id is InputRequired()
            id = form.id.data

            model = self.get_one(id)

            if model is None:
                flash(gettext('Record does not exist.'))
                return redirect(return_url)

            # message is flashed from within delete_model if it fails
            if self.delete_model(model):
                flash(gettext('Record was successfully deleted.'))
                return redirect(return_url)
        else:
            flash_errors(form, message='Failed to delete record. %(error)s')

        return redirect(return_url)

    @expose('/action/', methods=('POST',))
    def action_view(self):
        """
            Mass-model action view.
        """
        return self.handle_action()

    def _export_data(self):
        # Macros in column_formatters are not supported.
        # Macros will have a function name 'inner'
        # This causes non-macro functions named 'inner' not work.
        for col, func in iteritems(self.column_formatters_export):
            # skip checking columns not being exported
            if col not in [col for col, _ in self._export_columns]:
                continue

            if func.__name__ == 'inner':
                raise NotImplementedError(
                    'Macros are not implemented in export. Exclude column in'
                    ' column_formatters_export, column_export_list, or '
                    ' column_export_exclude_list. Column: %s' % (col,)
                )

        # Grab parameters from URL
        view_args = self._get_list_extra_args()

        # Map column index to column name
        sort_column = self._get_column_by_idx(view_args.sort)
        if sort_column is not None:
            sort_column = sort_column[0]

        # Get count and data
        count, data = self.get_list(0, sort_column, view_args.sort_desc,
                                    view_args.search, view_args.filters,
                                    page_size=self.export_max_rows)

        return count, data

    @expose('/export/<export_type>/')
    def export(self, export_type):
        return_url = get_redirect_target() or self.get_url('.index_view')

        if not self.can_export or (export_type not in self.export_types):
            flash(gettext('Permission denied.'))
            return redirect(return_url)

        if export_type == 'csv':
            return self._export_csv(return_url)
        else:
            return self._export_tablib(export_type, return_url)

    def _export_csv(self, return_url):
        """
            Export a CSV of records as a stream.
        """
        count, data = self._export_data()

        # https://docs.djangoproject.com/en/1.8/howto/outputting-csv/
        class Echo(object):
            """
            An object that implements just the write method of the file-like
            interface.
            """
            def write(self, value):
                """
                Write the value by returning it, instead of storing
                in a buffer.
                """
                return value

        writer = csv.writer(Echo())

        def generate():
            # Append the column titles at the beginning
            titles = [csv_encode(c[1]) for c in self._export_columns]
            yield writer.writerow(titles)

            for row in data:
                vals = [csv_encode(self.get_export_value(row, c[0]))
                        for c in self._export_columns]
                yield writer.writerow(vals)

        filename = self.get_export_name(export_type='csv')

        disposition = 'attachment;filename=%s' % (secure_filename(filename),)

        return Response(
            stream_with_context(generate()),
            headers={'Content-Disposition': disposition},
            mimetype='text/csv'
        )

    def _export_tablib(self, export_type, return_url):
        """
            Exports a variety of formats using the tablib library.
        """
        if tablib is None:
            flash(gettext('Tablib dependency not installed.'))
            return redirect(return_url)

        filename = self.get_export_name(export_type)

        disposition = 'attachment;filename=%s' % (secure_filename(filename),)

        mimetype, encoding = mimetypes.guess_type(filename)
        if not mimetype:
            mimetype = 'application/octet-stream'
        if encoding:
            mimetype = '%s; charset=%s' % (mimetype, encoding)

        ds = tablib.Dataset(headers=[c[1] for c in self._export_columns])

        count, data = self._export_data()

        for row in data:
            vals = [self.get_export_value(row, c[0]) for c in self._export_columns]
            ds.append(vals)

        try:
            try:
                response_data = ds.export(format=export_type)
            except AttributeError:
                response_data = getattr(ds, export_type)
        except (AttributeError, tablib.UnsupportedFormat):
            flash(gettext('Export type "%(type)s not supported.',
                          type=export_type))
            return redirect(return_url)

        return Response(
            response_data,
            headers={'Content-Disposition': disposition},
            mimetype=mimetype,
        )

    @expose('/ajax/lookup/')
    def ajax_lookup(self):
        name = request.args.get('name')
        query = request.args.get('query')
        offset = request.args.get('offset', type=int)
        limit = request.args.get('limit', 10, type=int)

        loader = self._form_ajax_refs.get(name)

        if not loader:
            abort(404)

        data = [loader.format(m) for m in loader.get_list(query, offset, limit)]
        return Response(json.dumps(data), mimetype='application/json')

    @expose('/ajax/update/', methods=('POST',))
    def ajax_update(self):
        """
            Edits a single column of a record in list view.
        """
        if not self.column_editable_list:
            abort(404)

        form = self.list_form()

        # prevent validation issues due to submitting a single field
        # delete all fields except the submitted fields and csrf token
        for field in form:
            if (field.name in request.form) or (field.name == 'csrf_token'):
                pass
            else:
                form.__delitem__(field.name)

        if self.validate_form(form):
            pk = form.list_form_pk.data
            record = self.get_one(pk)

            if record is None:
                return gettext('Record does not exist.'), 500

            if self.update_model(form, record):
                # Success
                return gettext('Record was successfully saved.')
            else:
                # Error: No records changed, or problem saving to database.
                msgs = ", ".join([msg for msg in get_flashed_messages()])
                return gettext('Failed to update record. %(error)s',
                               error=msgs), 500
        else:
            for field in form:
                for error in field.errors:
                    # return validation error to x-editable
                    if isinstance(error, list):
                        return gettext('Failed to update record. %(error)s',
                                       error=", ".join(error)), 500
                    else:
                        return gettext('Failed to update record. %(error)s',
                                       error=error), 500
