Type-Safety

If you are using TypeScript, and you wish to get a better integration for GraphQL and TypeScript while writing your API and resolvers, we have a few tools that might make it simple for you.

Shaping Context Type

GraphQL Modules exposes a global namespace called GraphQLModules, so there’s no need to pass the same signature over and over again as part of generic types of different APIs. This namespace includes the Context type.

GraphQLModules.Context is a global interface exposed for you by GraphQL Modules and allows you to easily type your context object. It’s global and shared across modules and application which means you can define it once, and it applies automatically everywhere.

To extend GraphQLModules.Context, add a declaration statement in your code to add new type properties to GraphQLModules.GlobalContext (which makes up part of GraphQLModules.Context):

declare global {
  namespace GraphQLModules {
    interface GlobalContext {
      request: RequestType
      customData: customDataType
    }
  }
}

Now every piece of GraphQL Modules understands the context type, and you gain much stronger type safety. Changes to GraphQLModules.Context will get updated automatically wherever it is used.

Using Context Type

Now that you’ve extended the Context type based on your actual context shape, you can use GraphQLModules.Context while writing your resolvers.

Using GraphQLModules.Context is simple and because GraphQL Modules makes it a globally available type, you just use it, there’s no need to import it from graphql-modules package. You can use it directly in your resolvers by typing the context argument:

const resolvers = {
  Query: {
    myQuery(root, args, context: GraphQLModules.Context, info) {
      // ...
    }
  }
}

Or assign it globally with Graphql Code Generator:

schema: './src/modules/*.graphql'
generates:
  ./src/modules/:
    preset: graphql-modules
    config:
      contextType: 'GraphQLModules.Context' # Your extended context type!
    presetConfig:
      baseTypesPath: ../generated/schema-types.ts
      filename: generated/module-types.ts
    plugins:
      - typescript
      - typescript-resolvers
    # ...

Strict Resolvers Types

If you wish to have even more control over your implementation, you can use GraphQL-Code-Generator to generate resolvers signature types per each module you write. This is useful because this way you can find issues during development/build time, and get complete type-safety and auto-complete in your IDE.

We created a special GraphQL-Code-Generator preset for that purpose. It generates a complete, unified, type signature for your schema, and sub-files per each module, containing only the GraphQL types declared/extended in your specific module.

To get started, follow the instructions in graphql-code-generator.com website.