GraphQL error format - Mini Project: Build & Apply

GraphQL Error Format

📖 Scenario: You are building a GraphQL API for a simple online bookstore. When a client sends a query with invalid data or requests a book that does not exist, your API should return errors in the standard GraphQL error format.

🎯 Goal: Create a GraphQL error response that follows the official GraphQL error format, including message, locations, and path fields.

📋 What You'll Learn

Create an error object with a message field describing the error

Include a locations array with line and column numbers where the error occurred

Add a path array showing the query path that caused the error

💡 Why This Matters

🌍 Real World

GraphQL APIs use this error format to inform clients about problems in queries or mutations clearly and consistently.

💼 Career

Understanding GraphQL error formatting is essential for backend developers building APIs and frontend developers handling API errors gracefully.

1

Create the basic error message

Create a JSON object called error with a message field set to "Book not found".

GraphQL

{
  "message": "Book not found"
  // Your code here
}

Hint

The error object must have a message field with the exact text "Book not found".

2

Add error location information

Add a locations field to the error object. It should be an array with one object containing "line": 3 and "column": 5.

GraphQL

{
  "message": "Book not found",
  "locations": [
    {
      "line": 3,
      "column": 5
    }
  ]
  // Your code here
}

Hint

The locations field is an array with one object specifying the line and column numbers.

3

Add the error path

Add a path field to the error object. It should be an array with the strings "queryBook" and "id".

GraphQL

{
  "message": "Book not found",
  "locations": [
    {
      "line": 3,
      "column": 5
    }
  ],
  "path": ["queryBook", "id"]
  // Your code here
}

Hint

The path field shows the query path as an array of strings.

4

Complete the GraphQL error response

Wrap the error object inside a JSON object with the key errors as an array containing the error object.

GraphQL

{
  "errors": [
    {
      "message": "Book not found",
      "locations": [
        {
          "line": 3,
          "column": 5
        }
      ],
      "path": ["queryBook", "id"]
    }
  ]
  // Your code here
}

Hint

The final response wraps the error object inside an errors array.

Practice

1. What is the main purpose of the message field in a GraphQL error response?

easy

A. To describe what went wrong in the query

B. To show the exact line of code where the error occurred

C. To list all the fields requested in the query

D. To provide the user's authentication token

Solution

1. Step 1: Understand the role of the message field

   The message field clearly states the error description to help identify the problem.

2. Step 2: Compare with other fields

   Other fields like location show where the error happened, but message explains what the error is.

3. Final Answer:

   To describe what went wrong in the query -> Option A

4. Quick Check:

   message = error description [OK]

Hint: Message always explains the error clearly [OK]

Common Mistakes:

• Confusing message with location
• Thinking message holds query data
• Assuming message is optional

2. Which of the following is the correct structure of a GraphQL error object?

easy

A. { message: string, location: string, path: string }

B. { error: string, line: int, column: int, path: string }

C. { message: string, line: int, column: int, query: string }

D. { message: string, location: [{ line: int, column: int }], path: [string] }

Solution

1. Step 1: Recall GraphQL error object format

   GraphQL errors include message, location as an array of line and column objects, and path as an array of strings.

2. Step 2: Check each option's structure

   Only { message: string, location: [{ line: int, column: int }], path: [string] } matches the correct structure with proper types and nesting.

3. Final Answer:

   { message: string, location: [{ line: int, column: int }], path: [string] } -> Option D

4. Quick Check:

   Correct error object format = { message: string, location: [{ line: int, column: int }], path: [string] } [OK]

Hint: Look for location as array of line/column objects [OK]

Common Mistakes:

• Using location as a string
• Confusing path type with string instead of array
• Missing array brackets for location

3. Given this GraphQL error response snippet:

{"errors": [{"message": "Cannot query field 'age' on type 'User'", "locations": [{"line": 3, "column": 5}], "path": ["user", "age"]}]}

What does the path field indicate?

medium

A. The exact location in the query text where the error occurred

B. The sequence of fields leading to the error in the response data

C. The server file path where the error was logged

D. The user's file system path

Solution

1. Step 1: Understand the path field meaning

   The path shows the chain of fields in the response data that led to the error.

2. Step 2: Analyze the example path

   Here, the error is in the 'age' field inside the 'user' object, so path is ["user", "age"].

3. Final Answer:

   The sequence of fields leading to the error in the response data -> Option B

4. Quick Check:

   path = error location in response data [OK]

Hint: Path shows field chain causing error [OK]

Common Mistakes:

• Thinking path is query text location
• Confusing path with server file path
• Ignoring path as array of fields

4. You receive this GraphQL error response:

{"errors": [{"message": "Syntax Error: Expected Name, found }", "locations": [{"line": 5, "column": 10}]}]}

What is the most likely cause of this error?

medium

A. A missing or extra character in the query causing invalid syntax

B. A missing authentication token in the request headers

C. A server crash unrelated to the query

D. A network timeout error

Solution

1. Step 1: Interpret the error message

   The message says "Syntax Error: Expected Name, found }", indicating a syntax mistake in the query.

2. Step 2: Understand syntax errors in GraphQL

   Such errors happen when brackets, names, or punctuation are missing or misplaced in the query text.

3. Final Answer:

   A missing or extra character in the query causing invalid syntax -> Option A

4. Quick Check:

   Syntax error = query typo [OK]

Hint: Syntax errors mean query text is malformed [OK]

Common Mistakes:

• Assuming error is due to auth issues
• Confusing syntax error with server crash
• Ignoring location info in error

5. You want to add extra details to your GraphQL error responses for better debugging. Which field should you use to include custom error codes or metadata?

hard

A. locations

B. path

C. extensions

D. message

Solution

1. Step 1: Identify the field for extra error info

   The extensions field is designed to hold custom metadata like error codes or debugging info.

2. Step 2: Differentiate from other fields

   message is for error text, path shows error location in data, and locations shows query text position.

3. Final Answer:

   extensions -> Option C

4. Quick Check:

   extensions = custom error metadata [OK]

Hint: Use extensions for custom error details [OK]

Common Mistakes:

• Putting custom info in message
• Confusing path with metadata
• Ignoring extensions field existence