GraphQL error format

Introduction

GraphQL error format shows problems clearly when something goes wrong in a query. It helps developers fix issues fast.

When a query asks for data that does not exist.

When a user sends wrong or incomplete information.

When the server has trouble processing the request.

When a required field is missing in the query.

When permissions prevent access to requested data.

Syntax

GraphQL

{
  "errors": [
    {
      "message": "Error message here",
      "locations": [
        { "line": 2, "column": 3 }
      ],
      "path": ["fieldName"],
      "extensions": {
        "code": "ERROR_CODE",
        "details": "Additional info"
      }
    }
  ]
}

The errors field is an array because there can be many errors.

message explains what went wrong in simple words.

Examples

This error shows that the query asked for a field 'age' that does not exist on 'User'.

GraphQL

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

This error tells the user that the 'email' field is missing in the input.

GraphQL

{
  "errors": [
    {
      "message": "Field 'email' is required.",
      "locations": [{ "line": 2, "column": 3 }],
      "path": ["createUser"],
      "extensions": {
        "code": "BAD_USER_INPUT"
      }
    }
  ]
}

Sample Program

This query asks for 'name' and 'age' of a user. The server replies with an error because 'age' is not a valid field.

GraphQL

query {
  user(id: "123") {
    name
    age
  }
}

/*
Server response:
{
  "errors": [
    {
      "message": "Cannot query field 'age' on type 'User'.",
      "locations": [{ "line": 4, "column": 5 }],
      "path": ["user", "age"],
      "extensions": {
        "code": "GRAPHQL_VALIDATION_FAILED"
      }
    }
  ]
}
*/

Important Notes

The locations help find the exact spot in the query where the error happened.

The path shows which part of the query caused the error.

Extensions provide extra info like error codes to help handle errors programmatically.

Summary

GraphQL errors are returned in a clear, structured format.

Errors include message, location, path, and optional extensions.

This format helps developers quickly find and fix problems in queries.

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