Schema linting in GraphQL - Mini Project: Build & Apply

GraphQL Schema Linting

📖 Scenario: You are working on a GraphQL API for a book store. You want to make sure your schema is clean and follows good practices before sharing it with your team.

🎯 Goal: Build a simple GraphQL schema and add linting rules to check for common issues like missing descriptions and consistent naming.

📋 What You'll Learn

Create a GraphQL schema with types for Book and Author

Add a configuration variable to enable linting rules

Write a linting function that checks for missing descriptions on types and fields

Complete the linting setup to output linting results for the schema

💡 Why This Matters

🌍 Real World

GraphQL schema linting helps teams maintain clean, consistent API definitions that are easier to understand and maintain.

💼 Career

Many companies use GraphQL for APIs; knowing how to write and lint schemas is valuable for backend and full-stack developers.

1

Create the GraphQL schema

Create a GraphQL schema string called schema with these exact types: Book with fields id: ID!, title: String!, and author: Author!; and Author with fields id: ID! and name: String!.

GraphQL

# Your code here

Hint

Define the schema as a multiline string with the exact types and fields.

2

Add linting configuration

Create a variable called linting_enabled and set it to True to enable linting.

GraphQL

schema = """
type Book {
  id: ID!
  title: String!
  author: Author!
}

type Author {
  id: ID!
  name: String!
}
"""

# Your code here

Hint

Just create a boolean variable named linting_enabled and set it to True.

3

Write linting function

Write a function called lint_schema that takes schema as input and returns a list called issues. The function should check if the schema string contains the word "description". If not, add the string "Missing descriptions in schema" to issues. Return issues.

GraphQL

schema = """
type Book {
  id: ID!
  title: String!
  author: Author!
}

type Author {
  id: ID!
  name: String!
}
"""

linting_enabled = True

def lint_schema(schema):
    # Your code here

Hint

Check if the word description is missing in the schema string and add a message to the list.

4

Complete linting setup

Add code that checks if linting_enabled is True. If yes, call lint_schema(schema) and store the result in a variable called lint_results.

GraphQL

schema = """
type Book {
  id: ID!
  title: String!
  author: Author!
}

type Author {
  id: ID!
  name: String!
}
"""

linting_enabled = True

def lint_schema(schema):
    issues = []
    if "description" not in schema:
        issues.append("Missing descriptions in schema")
    return issues

if linting_enabled:
    # Your code here

Hint

Use an if statement to check linting_enabled and call the lint function.

Practice

1. What is the main purpose of schema linting in GraphQL?

easy

A. To generate database tables automatically

B. To execute queries faster

C. To check the schema for mistakes and style issues

D. To encrypt data in the schema

Solution

1. Step 1: Understand schema linting role

   Schema linting is used to find errors and style problems in GraphQL schemas.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated tasks like query speed, database creation, or encryption.

3. Final Answer:

   To check the schema for mistakes and style issues -> Option C

4. Quick Check:

   Schema linting = check mistakes and style [OK]

Hint: Linting means checking code or schema for errors [OK]

Common Mistakes:

• Confusing linting with query execution
• Thinking linting creates database tables
• Assuming linting encrypts data

2. Which of the following is a correct way to define a linting rule for a GraphQL schema?

easy

A. schemaLint: off

B. lintSchema = false

C. enableLinting = 0

D. "no-unused-types": true

Solution

1. Step 1: Identify correct lint rule syntax

   Linting rules are usually defined as key-value pairs like "no-unused-types": true.

2. Step 2: Check other options for syntax errors

   Options A, B, and D use invalid or incorrect syntax for linting rules.

3. Final Answer:

   "no-unused-types": true -> Option D

4. Quick Check:

   Lint rule syntax = key: value [OK]

Hint: Lint rules use key-value pairs like "rule-name": true [OK]

Common Mistakes:

• Using assignment (=) instead of key-value pairs
• Using invalid property names
• Turning off linting with wrong syntax

3. Given this linting configuration snippet:

{
  "no-deprecated-fields": true,
  "require-description": true
}

What will happen if the schema uses a deprecated field without a description?

medium

A. Linting will pass without errors

B. Linting will report errors for both deprecated field and missing description

C. Linting will only check for missing descriptions

D. Linting will ignore deprecated fields

Solution

1. Step 1: Analyze linting rules

   "no-deprecated-fields": true means deprecated fields cause errors. "require-description": true means missing descriptions cause errors.

2. Step 2: Apply rules to schema case

   Schema has a deprecated field without description, so both rules trigger errors.

3. Final Answer:

   Linting will report errors for both deprecated field and missing description -> Option B

4. Quick Check:

   Both rules active = errors for both issues [OK]

Hint: Active lint rules cause errors for matching schema issues [OK]

Common Mistakes:

• Assuming lint ignores deprecated fields
• Thinking only one rule applies
• Believing missing description is allowed

4. You run a schema linter and get an error: Field 'userAge' is missing a description. Which fix will resolve this error?

medium

A. Add a description string above the 'userAge' field in the schema

B. Rename the field to 'ageUser'

C. Remove the 'userAge' field from the schema

D. Ignore the error and continue

Solution

1. Step 1: Understand the error meaning

   The error says the field lacks a description, so the linter expects a comment or description string.

2. Step 2: Choose the fix that adds description

   Adding a description string above the field satisfies the linter. Renaming or removing the field or ignoring the error does not fix the missing description.

3. Final Answer:

   Add a description string above the 'userAge' field in the schema -> Option A

4. Quick Check:

   Missing description = add description [OK]

Hint: Add descriptions as comments to fix missing description errors [OK]

Common Mistakes:

• Renaming field instead of adding description
• Deleting field unnecessarily
• Ignoring lint errors

5. You want to enforce that all GraphQL schema types have descriptions and no unused types exist. Which combined linting configuration achieves this?

hard

A. { "require-description": true, "no-unused-types": true }

B. { "allow-unused-types": true, "require-description": false }

C. { "no-deprecated-fields": true, "allow-unused-types": false }

D. { "require-description": false, "no-unused-types": false }

Solution

1. Step 1: Identify rules for descriptions and unused types

   "require-description": true enforces descriptions. "no-unused-types": true disallows unused types.

2. Step 2: Match configuration to requirements

   { "require-description": true, "no-unused-types": true } sets both rules to true, matching the goal. Other options disable one or both rules.

3. Final Answer:

   { "require-description": true, "no-unused-types": true } -> Option A

4. Quick Check:

   Both rules true = enforce descriptions and no unused types [OK]

Hint: Set both rules true to enforce descriptions and no unused types [OK]

Common Mistakes:

• Disabling required rules
• Confusing allow and no rules
• Partial enforcement only