Introduction

Goal: The goal of this tutorial is to introduce you to GraphQL schemas, how to define them, and understand the different types of data that can be included in a schema. We'll also cover defining relationships between types.

Learning Outcomes: By the end of this tutorial, you will be able to create a basic GraphQL schema, understand different data types, and define relationships between these types.

Prerequisites: Basic knowledge of JavaScript is required. Familiarity with GraphQL basics would be beneficial but is not mandatory.

Step-by-Step Guide

What is a GraphQL Schema?

A GraphQL schema is a core component of a GraphQL server. It describes the types of data a client can query. It also defines the relationships between these types.

Defining a GraphQL Schema:

A schema is defined using the GraphQL Schema Definition Language (SDL). This includes types such as String, Integer, Boolean, ID, and Float. You can also have custom types.

Defining Relationships:

You can define relationships between types using fields. For example, a Post type might have a user field that links to a User type.

Code Examples

Example 1: Defining a Basic Schema

type Query {
    hello: String
}

This code defines a basic schema with a single Query type with a hello field of type String. This means clients can query hello and expect a string in return.

Example 2: Defining a Schema with a Custom Type and Relationship

type User {
    id: ID!
    name: String!
    posts: [Post!]
}

type Post {
    id: ID!
    title: String!
    user: User!
}

type Query {
    users: [User!]
    posts: [Post!]
}

This example shows how to define custom types (User and Post) and relationships between them. The User type has a posts field which is an array of Post types, and the Post type has a user field of type User.

The ! after a type means that field is non-nullable i.e., it must return a value.

Summary

Key Points:
1. GraphQL schemas define the data types and relationships a client can query.
2. Schemas use the GraphQL SDL to define types and relationships.
3. Relationships between types are defined using fields.

Next Steps: Start creating more complex schemas and query them using a GraphQL client.

Additional Resources:
1. GraphQL Official Documentation
2. How to GraphQL

Practice Exercises

Exercise 1: Define a schema for a Book type with fields id (ID type), title (String type), and author (Author type).

Exercise 2: Define a schema with Author type with id (ID type), name (String type), and books (array of Book type).

Solutions:

1. Book Schema
   graphql type Book { id: ID! title: String! author: Author! }

2. Author Schema
   graphql type Author { id: ID! name: String! books: [Book!] }

Tips: Try adding more fields to your types and experiment with different relationships.