Using schema directives

Using schema directives to transform schema types, fields, and arguments

A directive is an identifier preceded by a @ character, optionally followed by a list of named arguments, which can appear after almost any form of syntax in the GraphQL query or schema languages. Here’s an example from the GraphQL draft specification that illustrates several of these possibilities:

directive @deprecated(
  reason: String = "No longer supported"
) on FIELD_DEFINITION | ENUM_VALUE

type ExampleType {
  newField: String
  oldField: String @deprecated(reason: "Use `newField`.")
}

As you can see, the usage of @deprecated(reason: ...) follows the field that it pertains to (oldField), though the syntax might remind you of “decorators” in other languages, which usually appear on the line above. Directives are typically declared once, using the directive @deprecated ... on ... syntax, and then used zero or more times throughout the schema document, using the @deprecated(reason: ...) syntax.

Default Directives

GraphQL provides several default directives: @deprecated, @skip, and @include.

  • @deprecated(message: String) - marks field as deprecated with message
  • @skip(if: Boolean!) - GraphQL execution skips the field if true by not calling the resolver
  • @include(if: Boolean!) - Calls resolver for annotated field if true

Using custom schema directives

Import the implementation of the directive, then pass it to Apollo server via the schemaDirectives argument, which is an object that maps directive names to directive implementations:

const { ApolloServer, gql } = require('apollo-server');
const { RenameDirective } = require('rename-directive-package');

const typeDefs = gql`
type Person @rename(to: "Human") {
  name: String!
  currentDateMinusDateOfBirth: Int @rename(to: "age")
}`;

//Create and start your apollo server
const server = new ApolloServer({
  typeDefs,
  resolvers,
  schemaDirectives: {
    rename: RenameDirective,
  },
  app,
});

server.listen().then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
});

The implementation of RenameDirective takes care of changing the resolver and modifying the schema if necessary. To learn how to implement your own schema directives, read through this section.

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