flask admin custom QueryAjaxModelLoader

Question

From what I understand, Flask Admin supports AJAX use for foreign key model loading. The Flask Admin - Model Documentation covers the basics under the heading form_ajax_refs. I have managed to use this successfully on many occasions, however I am having issues with the level of customisation that I hope to achieve. Let me elaborate.

I have a Product model, an Organisation model and a join table to relate them, defined as so:

class Product(Base):
    __tablename__ = "products"

    product_uuid = Column(UUID(as_uuid=True), primary_key=True)
    title = Column(String, nullable=False)
    description = Column(String, nullable=False)
    last_seen = Column(DateTime(timezone=True), nullable=False, index=True)
    price = Column(Numeric(precision=7, scale=2), nullable=False, index=True)

class Organisation(Base):
    __tablename__ = "organisations"
    org_id = Column(String, primary_key=True)
    org_name = Column(String, nullable=False)
    products = relationship(
        Product,
        secondary="organisation_products",
        backref="organisations"
    )

organisation_products_table = Table(
    "organisation_products",
    Base.metadata,
    Column("org_id", String, ForeignKey("organisations.org_id"), nullable=False),
    Column("product_uuid", UUID(as_uuid=True), ForeignKey("products.product_uuid"), nullable=False),
    UniqueConstraint("org_id", "product_uuid"),
    )

In a Flask Admin Model view of a model called CuratedList that has a foreign key constraint to the Product model, I am using form_ajax_refs in the form create view, to allow selection of dynamically loaded Product items.

form_ajax_refs = {"products": {"fields": (Product.title,)}}

This works nicely to show me ALL rows of the Product model.

My current requirement, however, is to only use the AJAX model loader to show products with a specific org_id, for example "Google".

Attempt No. 1

Override get_query function of the ModelView class to join on organisation_products_table and filter by org_id. This looks something like this:

def get_query(self):
    return (
        self.session.query(CuratedList)
        .join(
            curated_list_items_table,
            curated_list_items_table.c.list_uuid == CuratedList.list_uuid
        )
        .join(
            Product,
            Product.product_uuid == curated_list_items_table.c.product_uuid
        )
        .join(
            organisation_products_table,
            organisation_products_table.c.product_uuid == Product.product_uuid
        )
        .filter(CuratedList.org_id == "Google")
        .filter(organisation_products_table.c.org_id == "Google")
    )

Unfortunately, this does not solve the issue, and returns the same behaviour as:

def get_query(self):
    return (
        self.session.query(CuratedList)
        .filter(CuratedList.org_id == self._org_id)
    )

It does not affect the behaviour of form_ajax_refs.

Attempt No.2

The Flask Admin - Model Documentation mentions another way of using form_ajax_refs, which involves using the QueryAjaxModelLoader class.

In my second attempt, I subclass the QueryAjaxModelLoader class and try to override the values of it's model, session or fields variables. Something like this:

class ProductAjaxModelLoader(QueryAjaxModelLoader):
    def __init__(self, name, session, model, **options):
        super(ProductAjaxModelLoader, self).__init__(name, session, model, **options)

        fields = (
            session.query(model.title)
            .join(organisation_products_table)
            .filter(organisation_products_table.c.org_id == "Google")
        ).all()

        self.fields = fields
        self.model = model
        self.session = session

And then instead of the previous form_ajax_refs approach, I use my new AjaxModelLoader like so:

form_ajax_refs = {
    "products": ProductAjaxModelLoader(
        "products", db.session, Product, fields=['title']
    )
}

Unfortunately, whether overriding the values of session or model with my query returns no products from the AJAX loader, and overriding fields still returns all products; not just products of org_id "Google".

What I Hope to Not Resort to

I would like to be able to achieve this without having to create a new model for each org, as this will prove to be non-scalable and of bad design.

Any suggestions welcomed. Thanks.

Answer 1

Thanks to Joes comment to my original question, I have formulated a working solution:

Override AjaxModelLoader function get_list like so:

def get_list(self, term, offset=0, limit=DEFAULT_PAGE_SIZE):
    filters = list(
        field.ilike(u'%%%s%%' % term) for field in self._cached_fields
    )
    filters.append(Organisation.org_id == "Google")
    return (
        db.session.query(Product)
        .join(organisation_products_table)
        .join(Organisation)
        .filter(*filters)
        .all()
    )

Answer 2

After much trial and error, and thanks to the posts above, I present a generic way to pass in filters to the Ajax Model Loader.

Here is a generic class that enables filtering on the foreign key table.

from flask_admin.contrib.sqla.ajax import QueryAjaxModelLoader, DEFAULT_PAGE_SIZE

class FilteredAjaxModelLoader(QueryAjaxModelLoader):
    additional_filters = []

    def get_list(self, term, offset=0, limit=DEFAULT_PAGE_SIZE):
        filters = list(
            field.ilike(u'%%%s%%' % term) for field in self._cached_fields
        )
        for f in self.additional_filters:
            filters.append(f)
        # filters.append(User.list_id == 2) # Now this is passed in the constructor
        # filters.append(User.is_active == 'Y')
        return (
            db.session.query(self.model)
                .filter(*filters)
                .all()
        )

    def __init__(self, name, session, model, **options):
        super(FilteredAjaxModelLoader, self).__init__(name, session, model, **options)
        self.additional_filters = options.get('filters')

Usage:

Pass it into form_ajax_refs like you would QueryAjaxModelLoader

FilteredAjaxModelLoader('component', db.session, User, fields=['list_value'],
                                filters=[User.list_id == 2, User.is_active == 'Y'])

Hope that helps.