Smart Relationships

This is the official documentation of the forestadmin-agent-django and forestadmin-agent-flask Python agents.

Smart relationships are very different between the two versions of the Agent.

You can find the full documentation of relationship customization here.

Structure

Smart relationships on legacy agents were declared creating a smart field with a reference property but differed in the way that:

• Relationships to a single record (many-to-one or one-to-one) worked using the get function which needed to return a single record.

• Relationships to a list of records (one-to-many or many-to-many) worked by implementing all the CRUD routes on a router file.

The new system is completely different: it is based on primary keys and foreign keys.

Migrating

Relationships when the foreign key is accessible

Before

from app.models import Address
from django_forest.utils.collection import Collection

# Many to one relationships
class OrderForest(Collection):
    def load(self):
        self.fields = [
            {
                "field": "delivery_address",
                "type": "String",
                "reference": "Address.id",
                "get": self.get_delivery_address,
            }
        ]

    def get_delivery_address(self, obj):
        return obj.delivery_address

# Reverse relationship
class AddressForest(Collection):
    def load(self):
        self.fields = [
            {
                "field": "orders",
                "type": ["String"],
                "reference": "Order.id",
            }
        ]

# urls.py
from app.views import AddressOrders

urlpatterns = [
    path(
        '/forest/address/<pk>/relationships/orders',
        AddressOrdersView.as_view(),
        name='address_orders'
    ),
    # ...
]

# views.py
from django.http import JsonResponse
from django.views import generic
from django_forest.resources.utils.queryset import PaginationMixin
from django_forest.utils.schema.json_api_schema import JsonApiSchema

from app.models import Order

class AddressOrdersView(PaginationMixin, generic.ListView):
    def get(self, request, pk, *args, **kwargs):
        params = request.GET.dict()
        queryset = Orders.objects.filter(delivery_address_id=pk)

        # pagination
        queryset = self.get_pagination(params, queryset)

        # json api serializer
        Schema = JsonApiSchema.get('orders')
        data = Schema().dump(queryset, many=True)

        return JsonResponse(data, safe=False)

After

# Create the relationship
agent.customize_collection("order").add_many_to_one_relation(
    "delivery_address", "Address", "delivery_address_id"
)

# Create the reverse relationship
agent.customize_collection("Address").add_one_to_many_relation(
    "orders", "Order", "delivery_address_id"
)

Relationships when you need complex logic to get a foreign key

In this example, we want to create a relationship between the order collection and the address collection (assuming that it does not already exist in the database because depends on complex logic).

We can see that in the legacy agent, the delivery_address field was a smart field that returned the full address of the order, while in the new agent, we will create a computed field that will contain the address ID (the foreign key), and then create the relationship.

We won't be detailing the migration of a relation to a list of records here, but it is very similar to the one described below.

If the foreign key was already present in the database in a related table, use the import-rename-delete feature to move it to the correct collection instead of using a computed field.

This will be much faster and will not require In filter operators to be implemented (as unlike computed fields, imported fields are natively filterable and sortable).

Before

from app.models import Address
from django_forest.utils.collection import Collection

# Many to one relationships
class OrderForest(Collection):
    def load(self):
        self.fields = [
            {
                "field": "delivery_address",
                "type": "String",
                "reference": "Address.id",
                "get": self.get_delivery_address,
            }
        ]

    def get_delivery_address(self, obj):
        return Address.objects.filter( """complex_query""" )

After

from typing import List, Dict

from app.models import Address
from forestadmin.datasource_toolkit.context.collection_context import CollectionCustomizationContext
from forestadmin.datasource_toolkit.interfaces.records import RecordsDataAlias

def get_delivery_address_id(
    records: List[RecordsDataAlias], context: CollectionCustomizationContext
):
    addresses_by_order_id = Address.objects.filter("""complex_query_here""")
    return [addresses_by_order_id[order["id"]]["id"] for order in records]

# Create a computed field that will contain the address ID (the foreign key)
agent.customize_collection("order").add_field("delivery_address_id", {
    "column_type": "Number",
    "dependencies": ["id"],
    "get_values": get_delivery_address_id
}).replace_field_operator(
    # Make the field filterable (this is required for the relationship to work)
    "delivery_address_id", "in",
    lambda value, context: pass  # implement the reverse-lookup logic here
).add_many_to_one_relation(
    # Create the relationship
    "delivery_address", "Address", "delivery_address_id"
)