How to compute options of dropdown for column filter in Flask Admin?

Question

In Flask Admin, I got a column of String values (I can't change the DB definition). When filtering this column in the index view, the user should be able to select the value from a dropdown.

The possible options for the filter should be computed when the user selects the filter. So I need a way to set the options based on a custom model query. Querying is rather fast as the column is indexed.

The SQLA custom filter example only shows how to apply a custom filter, but not how to make the options of a filter dynamic.

Answer 1

You can use flask has_request_context function to check if request context exists in function which returns options tuple for the filter. It can help in a situation when options get from DB but request context not exist at that moment.

def _get_options_for_filter()
    if not has_request_context():
        return ()
    return tuple([(o.id, o.title) for o in Options.query.all()])

Answer 2

The options parameter can be a callable so do something like the following (using the example you've linked to):

def get_all_last_names():
    unique_last_names = User.query.with_entities(User.last_name.distinct().label("last_name")).order_by(User.last_name.asc()).all()
    return [(user.last_name, user.last_name) for user in unique_last_names]

class UserAdmin(sqla.ModelView):

    column_filters = [
        FilterEqual(column=User.last_name, name='Last Name', options=get_all_last_names),
    ]

    # This is probably NOT the correct way to refresh the filters cache
    @expose('/')
    def index_view(self):
        self._refresh_filters_cache()
        return super(UserAdmin, self).index_view()

See single file demo below. Add new users and they will appear in the 'Last Name' filter. As pointed out by @sortas this version doesn't work when using the app factory method.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

from flask_admin.contrib import sqla
from flask_admin import Admin, expose

# required for creating custom filters
from flask_admin.contrib.sqla.filters import BaseSQLAFilter, FilterEqual

app = Flask(__name__)

# Create dummy secrey key so we can use sessions
app.config['SECRET_KEY'] = '123456790'

# Create in-memory database
app.config['DATABASE_FILE'] = 'sample_db.sqlite'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///' + app.config['DATABASE_FILE']
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>'


# Create model
class User(db.Model):

    id = db.Column(db.Integer, primary_key=True)
    first_name = db.Column(db.String(100))
    last_name = db.Column(db.String(100))
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)

    # Required for admin interface. For python 3 please use __str__ instead.
    def __unicode__(self):
        return self.username


# Create custom filter class
class FilterLastNameBrown(BaseSQLAFilter):
    def apply(self, query, value, alias=None):
        if value == '1':
            return query.filter(self.column == "Brown")
        else:
            return query.filter(self.column != "Brown")

    def operation(self):
        return 'is Brown'


def get_options():
    return [('1', 'Yes'), ('0', 'No')]


def get_all_last_names():
    unique_last_names = User.query.with_entities(User.last_name.distinct().label("last_name")).order_by(
        User.last_name.asc()).all()
    return [(user.last_name, user.last_name) for user in unique_last_names]


# Add custom filter and standard FilterEqual to ModelView
class UserAdmin(sqla.ModelView):

    column_filters = [
        FilterEqual(column=User.last_name, name='Last Name', options=get_all_last_names),
        FilterLastNameBrown(column=User.last_name, name='Last Name', options=(('1', 'Yes'), ('0', 'No')))
    ]

    # This is probably NOT the correct way to refresh the filters cache
    @expose('/')
    def index_view(self):
        self._refresh_filters_cache()
        return super(UserAdmin, self).index_view()


admin = Admin(app, template_mode="bootstrap3")
admin.add_view(UserAdmin(User, db.session))


def build_sample_db():
    db.drop_all()
    db.create_all()
    user_obj1 = User(first_name="Paul", last_name="Brown", username="pbrown", email="paul@gmail.com")
    user_obj2 = User(first_name="Luke", last_name="Brown", username="lbrown", email="luke@gmail.com")
    user_obj3 = User(first_name="Serge", last_name="Koval", username="skoval", email="serge@gmail.com")

    db.session.add_all([user_obj1, user_obj2, user_obj3])
    db.session.commit()


if __name__ == '__main__':
    build_sample_db()
    app.run(port=5000, debug=True)

Single file example when using app factory.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

from flask_admin.contrib import sqla
from flask_admin import Admin, expose

# required for creating custom filters
from flask_admin.contrib.sqla.filters import BaseSQLAFilter, FilterEqual

db = SQLAlchemy()


class User(db.Model):

    id = db.Column(db.Integer, primary_key=True)
    first_name = db.Column(db.String(100))
    last_name = db.Column(db.String(100))
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)

    # Required for admin interface. For python 3 please use __str__ instead.
    def __unicode__(self):
        return self.username


# Create custom filter class
class FilterLastNameBrown(BaseSQLAFilter):
    def apply(self, query, value, alias=None):
        if value == '1':
            return query.filter(self.column == "Brown")
        else:
            return query.filter(self.column != "Brown")

    def operation(self):
        return 'is Brown'


def get_options():
    return [('1', 'Yes'), ('0', 'No')]


def get_all_last_names():
    unique_last_names = User.query.with_entities(User.last_name.distinct().label("last_name")).order_by(
        User.last_name.asc()).all()
    return [(user.last_name, user.last_name) for user in unique_last_names]


# Add custom filter and dynamic FilterEqual to ModelView
class UserAdmin(sqla.ModelView):

    column_filters = [
        FilterLastNameBrown(column=User.last_name, name='Last Name', options=(('1', 'Yes'), ('0', 'No')))
    ]

    def get_filters(self):
        _dynamic_filters = getattr(self, 'dynamic_filters', None)
        if _dynamic_filters:
            return (super(UserAdmin, self).get_filters() or []) + _dynamic_filters
        else:
            return super(UserAdmin, self).get_filters()

    @expose('/')
    def index_view(self):
        self.dynamic_filters = []
        self.dynamic_filters.extend([
            FilterEqual(column=User.last_name, name='Last Name', options=get_all_last_names),
            # Add further dynamic filters here
        ])
        self._refresh_filters_cache()
        return super(UserAdmin, self).index_view()


def create_app():

    app = Flask(__name__)

    # Create dummy secrey key so we can use sessions
    app.config['SECRET_KEY'] = '123456790'

    # Create in-memory database
    app.config['DATABASE_FILE'] = 'sample_db.sqlite'
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///' + app.config['DATABASE_FILE']
    app.config['SQLALCHEMY_ECHO'] = True
    db.init_app(app)
    admin = Admin(app, template_mode="bootstrap3")
    admin.add_view(UserAdmin(User, db.session))

    # Flask views
    @app.route('/')
    def index():
        return '<a href="/admin/">Click me to get to Admin!</a>'

    @app.before_first_request
    def build_sample_db():
        db.drop_all()
        db.create_all()
        user_obj1 = User(first_name="Paul", last_name="Brown", username="pbrown", email="paul@gmail.com")
        user_obj2 = User(first_name="Luke", last_name="Brown", username="lbrown", email="luke@gmail.com")
        user_obj3 = User(first_name="Serge", last_name="Koval", username="skoval", email="serge@gmail.com")

        db.session.add_all([user_obj1, user_obj2, user_obj3])
        db.session.commit()

    return app


if __name__ == '__main__':
    app = create_app()
    app.run(port=5000, debug=True)

Answer 3

Version for Flask app factories (create_app, current_app, app_context and so on) :)

# Dynamic filter update method for Flask app factories
# Override version of base _refresh_filters_cache method
def update_dynamic_filters(self, dynamic_filters):

    # Get base filters
    self._filters = self.get_filters()

    # Add dynamic filters (to the beginning)
    for dft in dynamic_filters:
        self._filters.insert(0, dft)

    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

# Update view every page reload (thanks to the @pjcunningham)
@expose('/')
def index_view(self):
    dynamic_filters = []
    # Working with db in app_context
    with app.app_context():
        # Adding dynamic filters
        dynamic_filters.append(
            FilterInList(
                column=Record.record_condition,
                name='Condition',
                options=[
                    (x[0], x[0])
                    for x in db.session.query(Record.record_condition)
                    .distinct()
                    .all()
                ],
            )
        )
    # Add dynamic filters to view
    self.update_dynamic_filters(dynamic_filters)
    return super(RecordView, self).index_view()