Field Nullability

By default, Grats makes all fields nullable in keeping with GraphQL best practices. By modeling fields as nullable by default, any error encountered when evaluating a resolver function/method will be caught by the GraphQL executor and returned as a null value with error metadata attached to the response.

This approach allows for maximally resilient network requests, since a single error will not take down the entire query; generally it will only affect the field that threw the error.

If you find this pervasive nullability makes client application development frustrating, you may wish to enable Semantic Nullability.

@killsParentOnException

However, there are some fields where it is necessary to have a non-nullable field, for example for id. In this case, you may add the docblock tag @killsParentOnException to the field. This will cause the field to be typed as non-nullable, but it comes at a price. Should the resolver throw, the error will bubble up to the first nullable parent.

caution

If @killsParentOnException is used too liberally, small errors can take down huge portions of your query.

/** @gqlType */
class MyType {
  /**
   * @gqlField
   * @killsParentOnException
   */
  myField(): string {
    if (Math.random() > 0.5) {
      throw new Error("Bang");
    }
    return "Whew!";
  }
}

Playground

Would extract:

type MyType {
  myField: String!
}

Changing the default

This behavior can be changed by setting the config option { "nullableByDefault": false }.

danger

Disabling nullableByDefault is equivalent to marking all non-nullable fields as @killsParentOnException.