Code generation from schema in GraphQL - Mini Project: Build & Apply

GraphQL Code Generation from Schema

📖 Scenario: You are building a simple GraphQL API for a bookstore. You want to generate the code for the schema that defines the data types and queries.

🎯 Goal: Create a GraphQL schema that defines a Book type and a query to get all books.

📋 What You'll Learn

Create a Book type with fields id (ID!), title (String!), and author (String!)

Create a Query type with a field books that returns a list of Book

Use proper GraphQL syntax for types and queries

💡 Why This Matters

🌍 Real World

GraphQL schemas define the structure of data clients can query in modern APIs, used in web and mobile apps.

💼 Career

Understanding schema design is essential for backend developers and API engineers working with GraphQL.

1

Define the Book type

Create a GraphQL type called Book with fields id of type ID!, title of type String!, and author of type String!.

GraphQL

# Define the Book type
# Your code here

Hint

Use type Book { ... } syntax and specify each field with its type and exclamation mark for required fields.

2

Define the Query type

Add a GraphQL Query type with a field called books that returns a list of Book objects (use square brackets).

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
}

# Define the Query type
# Your code here

Hint

Use type Query { books: [Book] } to define the query returning a list of books.

3

Add non-nullable list to books field

Modify the books field in the Query type to return a non-nullable list of non-nullable Book objects. Use [Book!]! syntax.

GraphQL

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  # Update books field type
  books: [Book]
  # Your code here
}

Hint

Use [Book!]! to indicate the list and its items cannot be null.

4

Complete the schema with a comment

Add a comment at the top of the schema that says # Bookstore GraphQL Schema.

GraphQL

# Your comment here

type Book {
  id: ID!
  title: String!
  author: String!
}

type Query {
  books: [Book!]!
}

Hint

Use # to add a comment line at the top.

Practice

1. What is the main purpose of code generation from a GraphQL schema?

easy

A. To delete unused database tables

B. To manually write all database queries

C. To automatically create code based on the GraphQL schema

D. To convert GraphQL queries into HTML pages

Solution

1. Step 1: Understand code generation concept

   Code generation means creating code automatically from a source, here the GraphQL schema.

2. Step 2: Identify the purpose in GraphQL context

   In GraphQL, code generation helps create types and queries automatically from the schema to save time.

3. Final Answer:

   To automatically create code based on the GraphQL schema -> Option C

4. Quick Check:

   Code generation = automatic code creation [OK]

Hint: Code generation means automatic code creation from schema [OK]

Common Mistakes:

• Thinking code generation means manual coding
• Confusing code generation with deleting tables
• Assuming it converts queries to HTML

2. Which of the following is the correct way to specify the schema file in a GraphQL code generator config?

easy

A. "schema => './schema.graphql'"

B. "schema = './schema.graphql'"

C. "schema: schema.graphql"

D. "schema: './schema.graphql'"

Solution

1. Step 1: Recall config syntax for GraphQL code generator

   The config uses key-value pairs with colon and string paths in quotes.

2. Step 2: Identify correct syntax

   "schema: './schema.graphql'" uses colon and quotes correctly: "schema: './schema.graphql'".

3. Final Answer:

   "schema: './schema.graphql'" -> Option D

4. Quick Check:

   Config uses colon and quotes for paths [OK]

Hint: Config uses colon and quotes for file paths [OK]

Common Mistakes:

• Using equals sign instead of colon
• Omitting quotes around file path
• Using arrow syntax which is invalid here

3. Given this config snippet:

{
  schema: './schema.graphql',
  generates: {
    './src/types.ts': { plugins: ['typescript'] }
  }
}

What will be generated after running the code generator?

medium

A. A JavaScript file with database connection code

B. A TypeScript file with types matching the GraphQL schema

C. An HTML file showing the schema documentation

D. A JSON file with raw schema data

Solution

1. Step 1: Analyze the config's generates section

   The config says to generate './src/types.ts' using the 'typescript' plugin.

2. Step 2: Understand what the 'typescript' plugin does

   This plugin creates TypeScript types based on the GraphQL schema.

3. Final Answer:

   A TypeScript file with types matching the GraphQL schema -> Option B

4. Quick Check:

   typescript plugin = TypeScript types file [OK]

Hint: Plugin name hints the generated file type [OK]

Common Mistakes:

• Confusing TypeScript with JavaScript output
• Expecting HTML or JSON instead of types
• Ignoring the plugin specified

4. You run the GraphQL code generator but get an error: "Cannot find schema file './schema.graphql'". What is the most likely cause?

medium

A. The schema file path in the config is incorrect or file is missing

B. The code generator does not support GraphQL schemas

C. The output file path is invalid

D. The plugins array is empty

Solution

1. Step 1: Understand the error message

   The error says it cannot find the schema file at the given path.

2. Step 2: Identify the cause

   This usually means the path is wrong or the file does not exist at that location.

3. Final Answer:

   The schema file path in the config is incorrect or file is missing -> Option A

4. Quick Check:

   File not found = wrong path or missing file [OK]

Hint: Check schema file path and existence first [OK]

Common Mistakes:

• Blaming plugins or output path
• Assuming code generator lacks schema support
• Ignoring file system errors

5. You want to generate both TypeScript types and React hooks from your GraphQL schema. Which config snippet correctly sets this up?

hard

A. {
schema: './schema.graphql',
generates: {
'./src/types.ts': { plugins: ['typescript'] },
'./src/hooks.ts': { plugins: ['typescript-react-apollo'] }
}
}

B. {
schema: './schema.graphql',
generates: {
'./src/types.ts': { plugins: ['typescript-react-apollo'] },
'./src/hooks.ts': { plugins: ['typescript'] }
}
}

C. {
schema: './schema.graphql',
generates: {
'./src/types.ts': { plugins: ['react-hooks'] },
'./src/hooks.ts': { plugins: ['typescript'] }
}
}

D. {
schema: './schema.graphql',
generates: {
'./src/types.ts': { plugins: ['typescript'] },
'./src/hooks.ts': { plugins: ['react-hooks'] }
}
}

Solution

1. Step 1: Identify plugins for types and hooks

   'typescript' plugin generates TypeScript types; 'typescript-react-apollo' generates React Apollo hooks.

2. Step 2: Match plugins to correct output files

   Types go to './src/types.ts' with 'typescript'; hooks go to './src/hooks.ts' with 'typescript-react-apollo'.

3. Final Answer:

   Config with 'typescript' for types and 'typescript-react-apollo' for hooks -> Option A

4. Quick Check:

   Correct plugins match output files [OK]

Hint: Match plugins to output files by their purpose [OK]

Common Mistakes:

• Swapping plugins between files
• Using non-existent plugins like 'react-hooks'
• Missing one of the required plugins