Tutorial: Working with Enums and Interfaces in GraphQL

1. Introduction

In this tutorial, we'll explore Enums and Interfaces in GraphQL. These special types provide more flexibility and abstraction in your GraphQL schema. By the end, you will understand when and how to use them for best results.

You will learn:
- What Enums and Interfaces are in GraphQL
- How to define and use them
- Best practices for working with Enums and Interfaces

Prerequisites:
- Basic understanding of GraphQL and its schema
- Basic programming knowledge

2. Step-by-Step Guide

Enums

In GraphQL, Enums, or Enumerations, are a special kind of scalar that is restricted to a specific set of allowed values. This allows you to:

• Validate that any arguments of this type are one of the allowed values
• Communicate through the type system that a field will always be one of a finite set of values

Here's an example:

enum Episode {
  NEWHOPE
  EMPIRE
  JEDI
}

Interfaces

Interfaces are abstract types that allow you to define fields that multiple types will have in common. They are useful when you have a group of related types that share common fields.

Here's an example:

interface Character {
  id: ID!
  name: String!
  friends: [Character]
  appearsIn: [Episode]!
}

3. Code Examples

Enums Example

enum Status {
  ACTIVE
  INACTIVE
  SUSPENDED
}

type User {
  id: ID!
  name: String!
  status: Status!
}

In this example, we have a Status Enum with values ACTIVE, INACTIVE, and SUSPENDED. In the User type, the status field must be one of the values defined in the Status Enum.

Interfaces Example

interface Vehicle {
  maxSpeed: Int!
}

type Car implements Vehicle {
  maxSpeed: Int!
  seats: Int!
}

type Plane implements Vehicle {
  maxSpeed: Int!
  wingspan: Int!
}

Here, both Car and Plane types implement the Vehicle interface. Hence, they both have a maxSpeed field. Additionally, Car has a seats field and Plane has a wingspan field.

4. Summary

In this tutorial, we covered Enums and Interfaces in GraphQL. You learned what they are, how to define and use them, and some best practices.

Your next steps could include diving deeper into other special types in GraphQL, such as Unions and Input types, or exploring more advanced features like mutations and subscriptions.

5. Practice Exercises

1. Define an Enum for days of the week and use it in a Schedule type.
2. Create an Animal interface with fields name and age, and implement it in Dog and Cat types.

Solutions

1. Enum for days of the week:

enum Day {
  MONDAY
  TUESDAY
  WEDNESDAY
  THURSDAY
  FRIDAY
  SATURDAY
  SUNDAY
}

type Schedule {
  day: Day!
  event: String!
}

1. Animal interface:

interface Animal {
  name: String!
  age: Int!
}

type Dog implements Animal {
  name: String!
  age: Int!
  breed: String!
}

type Cat implements Animal {
  name: String!
  age: Int!
  color: String!
}

Keep practicing to understand Enums and Interfaces better. Try to use them in your own GraphQL schemas. Happy learning!