Custom federation directives

Beyond @key, Apollo Federation v2 provides several directives that control field ownership and sharing between subgraphs. All are available as helpers in fastql.federation.

`@external` — fields owned by another subgraph

Mark a field as externally owned with external(). External fields must be declared for @requires to reference them but are not resolved by this subgraph.

from fastql import Field, Type
from fastql.federation import external, key, requires

@Type(directives=[key("id")])
class Product:
    id: str
    weight: float = Field(directives=[external()])

    @Field(directives=[requires("weight")])
    def shipping_estimate(self) -> float:
        return self.weight * 2.5

`@requires` — computed fields that depend on external data

requires(fields) declares that a field computation needs external field values to be fetched first. The router forwards those fields in the entity representation. provides(fields) tells the router that this subgraph can return the specified fields of a related entity without an extra round-trip.

from fastql.federation import key, provides

@Type(directives=[key("id")])
class Order:
    id: str
    product: "Product" = Field(directives=[provides("name price")])

`@shareable` — allow a field to be resolved by multiple subgraphs

By default, a non-entity object type’s fields may only be resolved by one subgraph. Apply shareable() to allow other subgraphs to also resolve those fields.

from fastql import Type
from fastql.federation import shareable

@Type(directives=[shareable()])
class Location:
    lat: float
    lon: float

`@override` — migrate a field from another subgraph

override(from_subgraph) signals that this subgraph now owns a field that was previously owned by another subgraph.

from fastql import Field, Type
from fastql.federation import key, override

@Type(directives=[key("id")])
class Product:
    id: str
    inventory: int = Field(directives=[override("inventory-service")])

`@inaccessible` — hide from the public schema

inaccessible() excludes a type or field from the composed public API while still making it available inside the federation for @requires / @provides.

`@tag` — annotate for contract filtering

tag(name) attaches a named tag used with Apollo Contracts to produce filtered schema variants.

Previous: Entity resolution — @key and reference resolvers.

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Custom federation directives

`@external` — fields owned by another subgraph

`@requires` — computed fields that depend on external data

`@shareable` — allow a field to be resolved by multiple subgraphs

`@override` — migrate a field from another subgraph

`@inaccessible` — hide from the public schema

`@tag` — annotate for contract filtering

​@external — fields owned by another subgraph

​@requires — computed fields that depend on external data

​@provides — eager-load related entity fields

​@shareable — allow a field to be resolved by multiple subgraphs

​@override — migrate a field from another subgraph

​@inaccessible — hide from the public schema

​@tag — annotate for contract filtering

`@external` — fields owned by another subgraph

`@requires` — computed fields that depend on external data

`@provides` — eager-load related entity fields

`@shareable` — allow a field to be resolved by multiple subgraphs

`@override` — migrate a field from another subgraph

`@inaccessible` — hide from the public schema

`@tag` — annotate for contract filtering