Adding custom fields with graphql.schema.ymlfor Drupal 8 , 9 , 10 , and 11

As you expand your headless Drupal application, tailoring the GraphQL schema to meet precise data requirements becomes essential. Adding custom fields via graphql.schema.yml enhances data flexibility and allows more specific queries that align closely with your application's needs. This lesson provides a comprehensive guide on configuring custom fields within your GraphQL schemas.

Why Use Custom Fields in GraphQL?

Custom fields enable developers to extend the default GraphQL schema, allowing queries that match any unique application logic or data considerations. This customization reduces client-side processing and boosts application performance by serving only the necessary data directly from the backend.

Prerequisites

Before adding custom fields, make sure you have completed the initial setup of GraphQL in Drupal and have a fundamental understanding of GraphQL schemas, as discussed in previous lessons.

Setting Up Custom Fields in graphql.schema.yml

The graphql.schema.yml file is where you define types, fields, and resolvers. These definitions are pivotal for tailoring GraphQL to meet specific data parameters.

Step 1: Define Custom Fields in graphql.schema.yml

Navigate to your custom module's directory and access the graphql.schema.yml file. Add custom fields by extending existing types or creating new ones. Here’s a concise example:

    types:
      Article:
        fields:
          nid: Int
          title: String
          customSummary:
            type: String
            resolve: '@@custom_summary_resolver'
    

In this snippet, customSummary is a newly introduced field under the Article type, referencing a resolver for data retrieval logic.

Step 2: Implement a Resolver for Custom Fields

Resolvers bridge schema definitions with the actual data in Drupal, defining how the fields will compute their values. Here’s how you could define a resolver for the customSummary field:

    <?php

    namespace Drupal\custom_graphql\GraphQL\Resolvers;

    use Drupal\node\Entity\Node;

    class CustomSummaryResolver {
      
        public function __invoke($value, $args, $context, $info) {
            // Assuming $value is a fully loaded node.
            return isset($value->body->summary) ? $value->body->summary : 'No summary available';
        }
    }
    

This resolver fetches the summary from the body field of a node if available or returns a default message otherwise.

Step 3: Register the Resolver

Ensure the resolver is accessible by defining it in your services file within the same custom module:

    services:
      custom_graphql.custom_summary_resolver:
        class: '\Drupal\custom_graphql\GraphQL\Resolvers\CustomSummaryResolver'
    

Registering services bridges your schema configuration with Drupal's service container, ensuring the resolver is callable when required by GraphQL.

Testing and Validating Custom Fields

Once your schema is configured, validate your new field by executing a GraphQL query using GraphiQL Explorer:

    {
      articleById(nid: 1) {
        nid
        title
        customSummary
      }
    }
    

Verify that the query returns expected results, confirming that the custom field behaves as implemented in the resolver.

Best Practices for Customizing GraphQL Schemas

• Keep It Modular: Maintain a well-structured schema by organizing custom fields logically according to their roles or data sources.
• Performance Considerations: Ensure resolvers are efficient and optimized, avoiding expensive calculations when unnecessary.
• Future-Proofing: Document schema customizations thoroughly to assist with maintainability and future enhancements.

Conclusion

Adding custom fields to your GraphQL schemas via graphql.schema.yml empowers you to tailor data communication specifically for your application needs, enhancing the precision and efficiency of data handling within a headless Drupal setup.

Preview of Next Lesson

In our next lesson, we'll delve into Using hook_graphql_schema_alter(). This hook offers additional flexibility to customize GraphQL schemas even further without touching core code—perfect for maintaining clean and adaptable projects. Continue following our series to deepen your mastery of GraphQL in Drupal!