Arguments

Any resolver argument that is typed with a valid GraphQL type will be inferred as a GraphQL argument. Grats will automatically generate the appropriate schema definition based on the type of the argument and its name.

/** @gqlType */
class MyType {
  /** @gqlField */
  myField(greeting: string): string {
    return `${greeting} World`;
  }
}

Functional style fields

In functional style fields, the source object must always be the first argument, so GraphQL arguments must come after the source object.

/** @gqlField */
export function userById(_: Query, id: string): User {
  return DB.getUserById(id);
}

Default values

TypeScript default values will be used to infer the default value for the argument in the schema. Note that the default value must be parasable as a valid GraphQL literal.

class MyClass {
  /** @gqlField */
  myField(greeting: string = "Hello"): string {
    return `${greeting} World`;
  }
}

Deprecated arguments

Optional arguments can be marked as @deprecated by using the @deprecated JSDoc tag:

class MyClass {
  /** @gqlField */
  myField(
    /** @deprecated Unused! */
    greeting?: string | null,
  ): string {
    return `Hello World`;
  }
}

Nullable arguments

If you define your argument as nullable in your GraphQL schema, graphql-js may pass either an explicit null if the user passes an explicit null or simply not define the argument if the user omits the argument or passes it a nullable variable which ends up not being passed to the operation.

To account for this, Grats will require that any argument that is either nullable (someArg: T | null) or optional (someArg?: T) be defined as both nullable and optional: someArg?: T | null.

This ensures your resolver code handles both possible cases.

The one exception is if your argument has a default value. In that case, you may opt to mark your argument as optional but not nullable.

/** @gqlField */
export function greeting(_: Query, name?: string = "Max"): string {
  return `Hello, ${name}`;
}

Will result in the following schema:

type Query {
  greeting(name: String! = "Max"): String!
}

Note that the name argument is marked as non-nullable in the schema. This means the user may not pass an explicit null, but if the argument is omitted, the default value will be used.

Object-map style fields

If you wish to match the graphql-js resolver signature more directly, you may also define your arguments using a single object argument. The argument may appear in any position, but may not be combined with positional GraphQL arguments. This is not Grats' recommended style, but it is fully supported.

/** @gqlType */
class MyType {
  /** @gqlField */
  myField(args: { greeting: string }): string {
    return `${args.greeting} World`;
  }
}

Default values in this style can be defined by using the = operator with destructuring. Note that you must perform the destructuring in the argument list, not in the function body:

class MyClass {
  /** @gqlField */
  myField({ greeting = "Hello" }: { greeting: string }): string {
    return `${greeting} World`;
  }
}

Like positional arguments, object-map arguments can be marked as @deprecated by using the @deprecated JSDoc tag:

class MyClass {
  /** @gqlField */
  myField(_: {
    /** @deprecated Unused! */
    greeting?: string;
  }): string {
    return `Hello World`;
  }
}