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Definition

directive @link(
  as: String,
  for: link__Purpose,
  import: [link__Import],
  url: String!
) repeatable on SCHEMA

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Arguments

ArgumentTypeDescription
import[link__Import]The name of the directive to import with leading @ or a valid object (see import validation).
urlString!The feature URL for the import (see URL validation.

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Overview

The @link directive allows the importing of other directives. This is necessary to propagate a (custom) directive into the router schema through the @composeDirective directive.

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Usage

WunderGraph Cosmo does not currently support renaming federation directives.
When using WunderGraph Cosmo, explicitly importing federation directives is not necessary. These directives are inferred and injected into the schema automatically. If importing a custom directive, the directive definition must still be provided in the schema if the directive is used within the subgraph schema. For example: 
# subgraph 1
schema
@link(import: ["@shareable"], url: "https://specs.apollo.dev/federation/v2.3")
@link(import: ["@myDirective"], url: "https://company.org/my-feature/myDirective/v1.0") {
  query: Query
}

directive @myDirective on FIELD_DEFINITION

type Query @shareable {
    echo(string: String!): String! @myDirective
}
For brevity, “composing a directive” will henceforth serve as a substitute for providing the name of an imported an defined directive to the name argument of a @composeDirective.

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Validation

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Import validation

Directives are imported through a list. List values can provided in one of two ways:
  • A string of the directive name (with leading @)
  • An object of the following form:
input link__Import {
  name: String!
  as: String
}
Any other type of value will result in a composition error. If renaming an import, the import must also begin with a leading @. An example valid import might be: 
# subgraph 1
extend schema @link(
  import: ["@myDirective", { name: "@anotherDirective", as: "@hello" }],
  url: "https://company.org/directives/v1.0"
)

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URL validation

A URL must contain a path component, a feature component, and end with a version component. The version component must strictly match the format vMajor.Minor where Major and Minor represent integers, e.g., v1.2. An example valid URL might be: 
# subgraph 1
extend schema @link(
  import: ["@myDirective"],
  url: "https://path/feature-name/v1.2"
)

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Errors

@link will produce composition error(s) if:
  • A feature URL is invalid.
  • The same base feature URL is used across subgraphs but the major versions do not match.
  • An import value is not a valid string (@{string}) or object ({ name: String! as: String }) form.
  • A directive name (or its renamed value) do not both start with leading @.