Skip to content

Code Generation

The DGS Code Generation plugin generates code during your project’s build process based on your Domain Graph Service’s GraphQL schema file. The plugin generates the following:

  • Data types for types, input types, enums and interfaces.
  • A DgsConstants class containing the names of types and fields
  • Example data fetchers
  • A type safe query API that represents your queries

Quick Start

To apply the plugin, update your project’s build.gradle file to include the following:

// Using plugins DSL
plugins {
    id "" version "4.0.10"

Alternatively, you can set up classpath dependencies in your buildscript:

buildscript {
      classpath ''

apply plugin: ''

Next, you need to add the task configuration as shown here:

   schemaPaths = ["${projectDir}/src/main/resources/schema"] // List of directories containing schema files
   packageName = 'com.example.packagename' // The package name to use to generate sources
   generateClient = true // Enable generating the type safe query API

The plugin adds a generateJava Gradle task that runs as part of your project’s build. generateJava generates the code in the project’s build/generated directory. This folder is automatically added to the project's classpath. Types are available as part of the package specified by the packageName.types, where you specify the value of packageName as a configuration in your build.gradle file. Please ensure that your project’s sources refer to the generated code using the specified package name.

generateJava generates the data fetchers and places them in build/generated-examples.

NOTE: generateJava does NOT add the data fetchers that it generates to your project’s sources. These fetchers serve mainly as a basic boilerplate code that require further implementation from you.

You can exclude parts of the schema from code-generation by placing them in a different schema directory that is not specified as part of the schemaPaths for the plugin.

Mapping existing types

Codegen tries to generate a type for each type it finds in the schema, with a few exceptions.

  1. Basic scalar types - are mapped to corresponding Java/Kotlin types (String, Integer etc.)
  2. Data and time types - are mapped to corresponding java.time classes
  3. PageInfo and RelayPageInfo - are mapped to graphql.relay classes
  4. Types mapped with a typeMapping configuration

When you have existing classes that you want to use instead of generating a class for a certain type, you can configure the plugin to do so using a typeMapping. The typeMapping configuration is a Map where each key is a GraphQL type and each value is a fully qualified Java/Kotlin type.

   typeMapping = ["MyGraphQLType": "com.mypackage.MyJavaType"]

Generating Client APIs

The code generator can also create client API classes. You can use these classes to query data from a GraphQL endpoint using Java. Java GraphQL clients are useful for server-to-server communication and testing.

Code generation creates a field-nameGraphQLQuery for each Query and Mutation field. The *GraphQLQuery query class contains fields for each parameter of the field. For each type returned by a Query or Mutation, code generation creates a *ProjectionRoot. A projection is a builder class that specifies which fields get returned.

The following is an example usage of a generated API:

GraphQLQueryRequest graphQLQueryRequest =
        new GraphQLQueryRequest(
            new TicksGraphQLQuery.Builder()
            new TicksConnectionProjection()

This API was generated based on the following schema. The edges and node types are because the schema uses pagination. The API allows for a fluent style of writing queries, with almost the same feel of writing the query as a String, but with the added benefit of code completion and type safety.

type Query @extends {
    ticks(first: Int, after: Int, allowCached: Boolean): TicksConnection

type Tick {
    id: ID
    route: Route
    date: LocalDate
    userStars: Int
    userRating: String
    leadStyle: LeadStyle
    comments: String

type Votes {
    starRating: Float
    nrOfVotes: Int

type Route {
    routeId: ID
    name: String
    grade: String
    style: Style
    pitches: Int
    votes: Votes
    location: [String]

type TicksConnection {
    edges: [TickEdge]

type TickEdge {
    cursor: String!
    node: Tick

Sending a Query

A GraphQLQueryRequest can be serialized to JSON and sent to a GraphQL endpoint. The following example uses RestTemplate with Metatron.

private RestTemplate dgsRestTemplate;
private ObjectMapper mapper = new ObjectMapper();

private static HttpEntity<String> httpEntity(String request) {
    HttpHeaders headers = new HttpHeaders();
    return new HttpEntity<>(request, headers);

Map<String, String> request = Collections.singletonMap("query", graphQLQueryRequest.serialize());

// Invoke REST call, and get the "ticks" from data.
JsonNode node =, HttpMethod.POST, httpEntity(mapper.writeValueAsString(request)),
        new ParameterizedTypeReference<JsonNode>() {

//Convert to the response type
TicksConnection ticks = mapper.convertValue(node, TicksConnection.class);