fix hybrid_property filter support, add example

examples/sqla-hybrid_property/README.rst

+Example of how to use (and filter on) a hybrid_property with the SQLAlchemy backend.
+
+Hybrid properties allow you to treat calculations (for example: first_name + last_name)
+like any other database column.
+
+To run this example:
+
+1. Clone the repository::
+
+    git clone https://github.com/flask-admin/flask-admin.git
+    cd flask-admin
+
+2. Create and activate a virtual environment::
+
+    virtualenv env
+    source env/bin/activate
+
+3. Install requirements::
+
+    pip install -r 'examples/sqla-hybrid_property/requirements.txt'
+
+4. Run the application::
+
+    python examples/sqla-hybrid_property/app.py
+
+The first time you run this example, a sample sqlite database gets populated automatically. To suppress this behaviour,
+comment the following lines in app.py:::
+
+    if not os.path.exists(database_path):
+        build_sample_db()

examples/sqla-hybrid_property/__init__.py

+

examples/sqla-hybrid_property/app.py

+from flask import Flask
+from flask_sqlalchemy import SQLAlchemy
+from sqlalchemy.ext.hybrid import hybrid_property
+
+import flask_admin as admin
+from flask_admin.contrib import sqla
+from flask_admin.contrib.sqla.filters import IntGreaterFilter
+
+# Create application
+app = Flask(__name__)
+
+# Create dummy secrey key so we can use sessions
+app.config['SECRET_KEY'] = '123456790'
+
+# Create in-memory database
+app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///sample_db_2.sqlite'
+app.config['SQLALCHEMY_ECHO'] = True
+db = SQLAlchemy(app)
+
+
+# Flask views
+@app.route('/')
+def index():
+    return '<a href="/admin/">Click me to get to Admin!</a>'
+
+
+class Screen(db.Model):
+    __tablename__ = 'screen'
+    id = db.Column(db.Integer, primary_key=True)
+    width = db.Column(db.Integer, nullable=False)
+    height = db.Column(db.Integer, nullable=False)
+
+    @hybrid_property
+    def number_of_pixels(self):
+        return self.width * self.height
+
+
+class ScreenAdmin(sqla.ModelView):
+    ''' Flask-admin can not automatically find a hybrid_property yet. You will
+        need to manually define the column in list_view/filters/sorting/etc.'''
+    list_columns = ['id', 'width', 'height', 'number_of_pixels']
+    column_sortable_list = ['id', 'width', 'height', 'number_of_pixels']
+
+    # make sure the type of your filter matches your hybrid_property
+    column_filters = [IntGreaterFilter(Screen.number_of_pixels,
+                                       'Number of Pixels')]
+
+
+# Create admin
+admin = admin.Admin(app, name='Example: SQLAlchemy2', template_mode='bootstrap3')
+admin.add_view(ScreenAdmin(Screen, db.session))
+
+if __name__ == '__main__':
+
+    # Create DB
+    db.create_all()
+
+    # Start app
+    app.run(debug=True)

examples/sqla-hybrid_property/requirements.txt

+Flask
+Flask-Admin
+Flask-SQLAlchemy

flask_admin/contrib/sqla/view.py

@@ -4,7 +4,7 @@ import inspect
 
 from sqlalchemy.orm.attributes import InstrumentedAttribute
 from sqlalchemy.orm import joinedload, aliased
-from sqlalchemy.sql.expression import desc
+from sqlalchemy.sql.expression import desc, ColumnElement
 from sqlalchemy import Boolean, Table, func, or_
 from sqlalchemy.exc import IntegrityError
 
@@ -550,8 +550,11 @@ class ModelView(BaseModelView):
         if attr is None:
             raise Exception('Failed to find field for filter: %s' % name)
 
-        # Figure out filters for related column
-        if hasattr(attr, 'property') and hasattr(attr.property, 'direction'):
+        # Figure out filters for related column, unless it's a hybrid_property
+        if isinstance(attr, ColumnElement):
+            warnings.warn(('Unable to scaffold the filter for %s, scaffolding '
+                           'for hybrid_property is not supported yet.') % name)
+        elif hasattr(attr, 'property') and hasattr(attr.property, 'direction'):
             filters = []
 
             for p in self._get_model_iterator(attr.property.mapper.class_):
@@ -620,7 +623,9 @@ class ModelView(BaseModelView):
         if isinstance(filter, sqla_filters.BaseSQLAFilter):
             column = filter.column
 
-            if self._need_join(column.table):
+            # hybrid_property joins are not supported yet
+            if (isinstance(column, InstrumentedAttribute) and
+                    self._need_join(column.table)):
                 self._filter_joins[column] = [column.table]
 
         return filter