Reuseable functions for handling of inherited pks

Two new functions on `contrib.sql.tools`:

  - `is_inherited_primary_key(prop)` : Returns True if the `ColumnProperty` **prop** is an inherited primary key. Occuring Exceptions are not handled but raised. *Should* work with arbitrary levels of inheritance.
  - `get_column_for_current_model(prop)` : Return the `Column` that belongs to the model of the `ColumnProperty` **prop**. So if the ColumnProperty is for the parent, the Column for the parent ist returned. If the ColumnProperty if for the Child, the Column for the child is returned. Works with arbitrary levels of inheritance.

`AdminModelConverter.convert()`  and `ModelView.scaffold_list_columns()` are adapted to use the new functions.

flask_admin/contrib/sqla/form.py

@@ -12,6 +12,7 @@ from flask.ext.admin._compat import iteritems
 
 from .validators import Unique
 from .fields import QuerySelectField, QuerySelectMultipleField, InlineModelFormList
+from .tools import is_inherited_primary_key, get_column_for_current_model
 
 try:
     # Field has better input parsing capabilities.
@@ -132,17 +133,8 @@ class AdminModelConverter(ModelConverterBase):
             if hasattr(prop, 'columns'):
                 # Check if more than one column mapped to the property
                 if len(prop.columns) != 1:
-                    # Check if all columns are primary keys and _one_ does not have a foreign key -> looks like joined
-                    # table inheritance: http://docs.sqlalchemy.org/en/latest/orm/inheritance.html with "standard
-                    # practice" of same column name
-                    if len([column for column in prop.columns if column.primary_key]) == len(prop.columns) and \
-                            len([column for column in prop.columns if column.foreign_keys]) == len(prop.columns)-1:
-                        # Get the column(s) of the current model - should always be only one, I think (but not sure)
-                        candidates = [column for column in prop.columns if column.expression == prop.expression]
-                        if len(candidates) != 1:
-                            raise TypeError('Can not convert multiple-column pk-Property (%s.%s)' % (model, prop.key))
-                        else:
-                            column = candidates[0]
+                    if is_inherited_primary_key(prop):
+                        column = get_column_for_current_model(prop)
                     else:
                         raise TypeError('Can not convert multiple-column properties (%s.%s)' % (model, prop.key))
                 else:

flask_admin/contrib/sqla/tools.py

@@ -25,3 +25,39 @@ def get_primary_key(model):
                     return p.key
 
     return None
+
+def is_inherited_primary_key(prop):
+    """
+        Return True, if the ColumnProperty is an inherited primary key
+
+        Check if all columns are primary keys and _one_ does not have a foreign key -> looks like joined
+        table inheritance: http://docs.sqlalchemy.org/en/latest/orm/inheritance.html with "standard
+        practice" of same column name.
+
+        :param prop: The ColumnProperty to check
+        :return: Boolean
+        :raises: Exceptions as they occur - no ExceptionHandling here
+    """
+    return len([column for column in prop.columns if column.primary_key]) == len(prop.columns) and \
+                len([column for column in prop.columns if column.foreign_keys]) == len(prop.columns)-1
+
+def get_column_for_current_model(prop):
+    """
+        Return the Column() of the ColumnProperty "prop", that refers to the current model
+
+        When using inheritance, a ColumnProperty may contain multiple columns. This function
+        returns the Column(), the belongs to the Model of the ColumnProperty - the "current"
+        model
+
+        :param prop: The ColumnProperty
+        :return: The column for the current model
+        :raises: TypeError if not exactely one Column() for the current model could be found.
+                    All other Exceptions not handled here but raised
+    """
+    candidates = [column for column in prop.columns if column.expression == prop.expression]
+    if len(candidates) != 1:
+        raise TypeError('Not exactly one column for the current model found. ' +
+                        'Found %d columns for property %s' % (len(candidates), prop))
+    else:
+        return candidates[0]
+

flask_admin/contrib/sqla/view.py

@@ -15,7 +15,7 @@ from flask.ext.admin._backwards import ObsoleteAttr
 
 from flask.ext.admin.contrib.sqla import form, filters, tools
 from .typefmt import DEFAULT_FORMATTERS
-
+from .tools import is_inherited_primary_key, get_column_for_current_model
 
 class ModelView(BaseModelView):
     """
@@ -310,25 +310,16 @@ class ModelView(BaseModelView):
             elif hasattr(p, 'columns'):
                 column_inherited_primary_key = False
                 if len(p.columns) != 1:
-                    # Check if all columns are primary keys and _one_ does not have a foreign key -> looks like joined
-                    # table inheritance: http://docs.sqlalchemy.org/en/latest/orm/inheritance.html with "standard
-                    # practice" of same column name
-                    if len([column for column in p.columns if column.primary_key]) == len(p.columns) and \
-                            len([column for column in p.columns if column.foreign_keys]) == len(p.columns)-1:
-                        # Get the column(s) of the current model - should always be only one, I think (but not sure)
-                        candidates = [column for column in p.columns if column.expression == p.expression]
-                        if len(candidates) != 1:
-                            raise TypeError('Can not convert multiple-column pk-Property (%s.%s)' % (model, p.key))
-                        else:
-                            column = candidates[0]
-                            column_inherited_primary_key = True
+                    if is_inherited_primary_key(p):
+                        column = get_column_for_current_model(p)
                     else:
                         raise TypeError('Can not convert multiple-column properties (%s.%s)' % (model, p.key))
                 else:
                     # Grab column
                     column = p.columns[0]
 
-                if column.foreign_keys and not column_inherited_primary_key:
+                # An inherited primary key has a foreign key as well
+                if column.foreign_keys and not is_inherited_primary_key(p):
                     continue
 
                 if not self.column_display_pk and column.primary_key: