Creating a GraphQL Schema: A Step-by-Step Tutorial

1. Introduction

In this tutorial, we are going to learn how to create a GraphQL schema. A GraphQL schema defines your data model and the operations that can be performed on your data.

At the end of this tutorial, you will understand:
- What a GraphQL schema is
- How to define types in a schema
- How to define relationships between types
- How to define operations that can be performed on the data

Prerequisites

• Basic knowledge of JavaScript
• Familiarity with Node.js
• Experience with REST APIs is helpful, but not required

2. Step-by-Step Guide

A GraphQL schema is at the core of any GraphQL server. It describes the functionality available to the clients which connect to it. The schema is written using the GraphQL Schema Definition Language (SDL).

Defining Types

In GraphQL, the data you can query is organized into types. The most basic components of a GraphQL schema are object types, which just represent a kind of object you can fetch from your service, and what fields it has.

For instance, let's create a Person type:

type Person {
  id: ID!
  name: String!
  age: Int!
}

Here, we've defined a Person object type with id, name, and age fields. The ID, String, and Int are built-in scalar types in GraphQL.

Defining Relationships

We can also define relationships using types. Let's say, each Person object is associated with a Book object:

type Book {
  title: String!
  author: Person!
}

Defining Operations

In GraphQL, we define operations using Query and Mutation types. The Query type is used for fetching data while the Mutation type is used for modifying data.

type Query {
  getPerson(id: ID!): Person
}

type Mutation {
  addPerson(name: String!, age: Int!): Person
}

3. Code Examples

Example: Defining a Schema

Let's define a schema with Person and Book types and some operations.

type Person {
  id: ID!
  name: String!
  age: Int!
  books: [Book!]
}

type Book {
  title: String!
  author: Person!
}

type Query {
  getPerson(id: ID!): Person
  getBook(title: String!): Book
}

type Mutation {
  addPerson(name: String!, age: Int!): Person
  addBook(title: String!, author: ID!): Book
}

In this schema, a Person has many Book objects and a Book has an Author who is a Person. The operations allow us to fetch a Person or a Book by their id or title, and to add a Person or a Book.

4. Summary

We've learned how to create a GraphQL schema by defining types, relationships, and operations.

Next Steps

You can practice by creating more complex schemas and operations. Try to create a schema for a blog application, for example, with User, Post, Comment types, and corresponding operations.

Additional Resources

• GraphQL Official Documentation
• How to GraphQL

5. Practice Exercises

1. Exercise: Create a GraphQL schema for a ToDo application. The application should have User and ToDo types. A User can have multiple ToDo items. Define necessary fields and operations.

2. Exercise: Modify the above schema to add a completed field to ToDo type and add mutations to mark a ToDo as completed.

3. Exercise: Create a GraphQL schema for a blog application where a User can have multiple Post objects and a Post can have multiple Comment objects.

Tips for further practice

• Try to implement the schemas you've designed in a GraphQL server.
• Use GraphQL clients such as GraphQL Playground or GraphiQL to test your schema and operations.