GraphQL Enums

Problem:

We want a user to have one of two possible roles: BASIC or PREMIUM.

Currently, a client could potentially set the role of the user to any arbitrary string, like CHICKEN, which would obviously not make sense in our app.

We need a mechanism to establish a contract that the user.role can only be set to a pre-approved value.

Solution:

Enums

Enums are a way to create a list of pre-approved values for a certain type. In our case, we want to define an enum named Role that contains two possible values: BASIC and PREMIUM.

This mechanism tells our program that a Role type can only ever have the value BASIC or PREMIUM.

Implementation:

How to use enums to improve our role-based permission system

Step 1

Define the Role enum in the top level of the schema.

	import { gql } from "apollo-server-express";
	import userSchema from "./user";
	import postSchema from "./post";
	import commentSchema from "./comment";
	const linkSchema = gql`
	scalar Date
	enum Role {
	BASIC
	PREMIUM
	}
	type Query {
	_: Boolean
	}
	type Mutation {
	_: Boolean
	}
	type Subscription {
	_: Boolean
	}
	`;
	export default [linkSchema, userSchema, postSchema, commentSchema];

view raw schema_index.js hosted with ❤ by GitHub

Step 2

Specify the Role enum as the return type for the role field on the User type (in schema/user.js).

	export default gql`
	extend type Query {
	...
	}
	extend type Mutation {
	...
	}
	type User {
	id: ID!
	username: String!
	email: String!
	posts: [Post!]
	role: Role! # our new Role type
	}
	`;

view raw schema_user.js hosted with ❤ by GitHub

Step 3

Use the Role enum as the argument type for our updateRole mutation:

	import { gql } from "apollo-server-express";
	export default gql`
	extend type Query {
	...
	}
	extend type Mutation {
	...
	updateRole(newRole: Role!): User! # enum as argument
	}
	type User {
	id: ID!
	username: String!
	email: String!
	posts: [Post!]!
	role: Role!
	}
	`;

view raw schema_user.js hosted with ❤ by GitHub

This has the added benefit of giving us autocomplete in GraphQL Playground when setting the user’s role with this mutation:

Sweet! Less room for error.