extend-schema.mdx

description
Learn how to create a custom plugin for GraphQL Code Generator. How to extend the GraphQL Schema?

How to extend the GraphQL Schema?

Each plugin can also specify addToSchema field, and to extend the GraphQLSchema with more types:

module.exports = {
  plugin(schema, documents, config) {
    const typesMap = schema.getTypeMap()

    return Object.keys(typesMap).join('\n')
  },
  addToSchema: /* GraphQL */ `
    type MyType {
      field: String
    }

    directive @myDirective on OBJECT
  `
}

It's useful when you wish to add things like declarative @directive to your GraphQLSchema, which affects only the output of the codegen.

For example, let's add a custom @directive that tells the codegen to ignore a specific type:

module.exports = {
  plugin(schema, documents, config, info) {
    const typesMap = schema.getTypeMap()

    return Object.keys(typesMap)
      .filter(typeName => {
        const type = typesMap[typeName]
        const { astNode } = type

        if (astNode?.directives?.find(d => d.name.value === 'ignore')) {
          return false
        }

        return true
      })
      .join('\n')
  },
  addToSchema: /* GraphQL */ `
    directive @ignore on OBJECT
  `
}