Introduction

In this tutorial, we will focus on creating a GraphQL schema using the Schema Definition Language (SDL). You'll learn the fundamentals of a GraphQL schema, how to structure it using SDL and gain a practical understanding of how to build schemas for your GraphQL servers.

By the end of this tutorial, you should be able to:

• Understand what a GraphQL schema is
• Create a basic GraphQL schema using SDL
• Understand the different types of GraphQL SDL

Prerequisites

To successfully follow along with this tutorial, you should have:

• Basic knowledge of JavaScript.
• Basic understanding of GraphQL.

Step-by-Step Guide

Understanding GraphQL Schema

A GraphQL schema is a contract between the client and the server. It defines the types of data a client can request from the server.

Creating a GraphQL Schema using SDL

GraphQL SDL (Schema Definition Language) is a language-agnostic way to describe the schema of your GraphQL server. It is human-readable and easy to understand, making it the preferred way to define schemas.

Here is how you can define a basic schema in SDL:

type Tweet {
  id: ID!
  body: String!
  date: String!
}

In the above example, Tweet is an object type with fields id, body, and date. Each field has a type, and ! indicates that the field is non-nullable.

Code Examples

Example 1: Defining Object Types

type Author {
  id: ID!
  name: String!
  tweets: [Tweet!]!
}

In this example, we define a new object type Author. We've also created a relationship between Author and Tweet types using an array. This means that an author can have multiple tweets.

Example 2: Defining Query Types

type Query {
  getTweet(id: ID!): Tweet
  getAuthor(id: ID!): Author
}

The Query type is a special type that lets us query data. Here, we've defined two queries getTweet and getAuthor that retrieve a single tweet and author respectively based on their id.

Summary

In this tutorial, we've covered the basics of creating a GraphQL schema using SDL. We've learned about object types, fields, and query types.

Your next steps should be learning about mutation and subscription types, which allow you to change data and subscribe to data changes respectively.

For additional resources, consider:

• GraphQL Official Documentation
• Apollo GraphQL Docs

Practice Exercises

1. Create a schema for a blog post and comments. A blog post should have a title, body, and author, and a comment should have a body and author.

2. Create a query type that retrieves a blog post based on its ID.

3. Create a query type that retrieves all comments for a blog post based on the post's ID.

# Solutions
# Exercise 1
type BlogPost {
  id: ID!
  title: String!
  body: String!
  author: Author!
}

type Comment {
  id: ID!
  body: String!
  author: Author!
}

# Exercise 2
type Query {
  getBlogPost(id: ID!): BlogPost
}

# Exercise 3
type Query {
  getComments(postId: ID!): [Comment!]!
}

For further practice, try creating schemas for different types of applications, such as a shopping cart, a todo list, etc.