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    graphql-transform-federation
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    2.2.0 • Public • Published

    graphql-transform-federation

    If you want to use GraphQL federation, but you can't rebuild your current GraphQL schema, you can use this transform to add GraphQL federation functionality to an existing schema. You need this when you are using a managed GraphQL service or a generated schema which doesn't support federation (yet).

    If you are using apollo-server or another schema builder that supports federation you don't need this transform you should add the federation directives directly.

    This transform will add the resolvers and directives to conform to the federation specification. Much of the federation sourcecode could be reused ensuring it is compliant to the specification.

    Check out the blogpost introducing graphql-tranform-federation for more background information.

    Architecture diagram for graphql-transform-federation

    Usage

    You can use this transform on a local or a remote GraphQL schema. When using a remote schema your service acts a middleware layer as shown in the diagram above. Check the remote schema documentation for how to get an executable schema that you can use with this transform.

    The example below shows a configuration where the transformed schema extends an existing schema. It already had a resolver productById which is used to relate products between the two schemas. This example can be started using npm run example.

    import { transformSchemaFederation } from 'graphql-transform-federation';
    import { delegateToSchema } from 'graphql-tools';
     
    const schemaWithoutFederation = // your existing executable schema
     
    const federationSchema = transformSchemaFederation(schemaWithoutFederation, {
      Query: {
        // Ensure the root queries of this schema show up the combined schema
        extend: true,
      },
      Product: {
        // extend Product {
        extend: true,
        // Product @key(fields: "id") {
        keyFields: ['id'],
        fields: {
          // id: Int! @external
          id: {
            external: true
          }
        },
        resolveReference({ id }, context, info) {
          return delegateToSchema({
            schema: info.schema,
            operation: 'query',
            fieldName: 'productById',
            args: {
              id,
            },
            context,
            info,
          });
        },
      },
    });

    To allow objects of an existing schema to be extended by other schemas it only needs to get @key(...) directives.

    const federationSchema = transformSchemaFederation(schemaWithoutFederation, {
      Product: {
        // Product @key(fields: "id") {
        keyFields: ['id'],
      },
    });

    API reference

    import { GraphQLSchema } from 'graphql';
    import { GraphQLReferenceResolver } from '@apollo/federation/dist/types';
     
    interface FederationFieldConfig {
      external?: boolean;
      provides?: string;
      requires?: string;
    }
     
    interface FederationFieldsConfig {
      [fieldName: string]: FederationFieldConfig;
    }
     
    interface FederationObjectConfig<TContext> {
      // An array so you can add multiple @key(...) directives
      keyFields?: string[];
      extend?: boolean;
      resolveReference?: GraphQLReferenceResolver<TContext>;
      fields?: FederationFieldsConfig;
    }
     
    interface FederationConfig<TContext> {
      [objectName: string]: FederationObjectConfig<TContext>;
    }
     
    function transformSchemaFederation<TContext>(
      schema: GraphQLSchema,
      federationConfig: FederationConfig<TContext>,
    ): GraphQLSchema;

    npm run example

    Runs 2 GraphQL servers and a federation gateway to combine both schemas. Transformed-server is a regular GraphQL schema that is tranformed using this library. The federation-server is a federation server which is extended by a type defined by the transformed-server. The gateway combines both schemas using the apollo gateway.

    npm run example:watch

    Runs the example in watch mode for development.

    npm run test

    Run the tests

    Keywords

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    Install

    npm i graphql-transform-federation

    DownloadsWeekly Downloads

    24,146

    Version

    2.2.0

    License

    ISC

    Unpacked Size

    53.8 kB

    Total Files

    22

    Last publish

    Collaborators

    • ruben.oostinga