Why error handling differs from REST in GraphQL - Quick Recap

Recall & Review

beginner

What is the main difference in error handling between GraphQL and REST?

GraphQL returns errors inside the response body alongside data, while REST uses HTTP status codes to indicate errors.

intermediate

How does GraphQL handle partial data when an error occurs?

GraphQL can return partial data with an errors array, allowing clients to receive some valid data even if parts failed.

intermediate

Why can't GraphQL rely solely on HTTP status codes for error handling?

Because GraphQL responses often return HTTP 200 OK even if there are errors, to allow partial data and errors in the same response.

beginner

In REST, what does an HTTP 404 status code usually mean?

It means the requested resource was not found on the server.

beginner

What is the purpose of the 'errors' field in a GraphQL response?

It provides detailed information about what went wrong during the query execution.

How does GraphQL typically indicate errors in a response?

A By returning an empty response

B Using HTTP status codes like 404 or 500

C Using an 'errors' field in the JSON response

D By closing the connection abruptly

GraphQL includes an 'errors' field in the JSON response to indicate errors, even when HTTP status is 200.

What HTTP status code does GraphQL usually return even if there are errors?

A 200 OK

B 404 Not Found

C 500 Internal Server Error

D 400 Bad Request

GraphQL typically returns HTTP 200 OK to allow partial data and errors in the same response.

In REST, what does an HTTP 500 status code indicate?

A Request was successful

B Resource not found

C Client error in request

D Server error occurred

HTTP 500 means a server error happened while processing the request.

Why might GraphQL return partial data with errors?

A To provide as much valid data as possible despite some errors

B Because it cannot detect errors

C To confuse the client

D Because it does not support errors

GraphQL returns partial data with errors to give clients useful information even if some parts failed.

Which of these is NOT a typical way REST handles errors?

A Returning error messages in the response body

B Returning an 'errors' field in JSON

C Using HTTP status codes

D Using different status codes for different error types

REST does not usually use an 'errors' field in JSON; it relies on HTTP status codes and message bodies.

Explain how error handling in GraphQL differs from REST and why GraphQL uses this approach.

Think about how clients receive data and errors in both systems.

Describe the role of the 'errors' field in a GraphQL response and how it helps clients handle errors.

Focus on the information provided to clients about errors.

Practice

1. In GraphQL, how are errors handled differently compared to REST APIs?

easy

A. GraphQL returns data and errors together in one response.

B. GraphQL stops execution and returns only errors without data.

C. GraphQL returns errors as HTTP status codes only.

D. GraphQL does not provide any error details to the client.

Solution

1. Step 1: Understand REST error handling

   REST APIs usually return errors as HTTP status codes and no data when an error occurs.

2. Step 2: Understand GraphQL error handling

   GraphQL returns both data and errors together in one response, allowing partial data delivery.

3. Final Answer:

   GraphQL returns data and errors together in one response. -> Option A

4. Quick Check:

   GraphQL response = data + errors [OK]

Hint: Remember GraphQL sends data and errors together [OK]

Common Mistakes:

• Thinking GraphQL only returns errors without data
• Confusing HTTP status codes with GraphQL error handling
• Assuming GraphQL hides error details

2. Which part of a GraphQL response contains error details?

easy

A. The data field

B. The HTTP status code

C. The errors field

D. The extensions field only

Solution

1. Step 1: Identify error location in GraphQL response

   GraphQL responses include an errors field that lists error messages and details.

2. Step 2: Differentiate from other fields

   The data field contains the requested data, HTTP status codes are not used for errors, and extensions may have extra info but not main errors.

3. Final Answer:

   The errors field -> Option C

4. Quick Check:

   Error details = errors field [OK]

Hint: Errors are always in the 'errors' field [OK]

Common Mistakes:

• Looking for errors in the data field
• Relying on HTTP status codes for errors
• Confusing extensions with errors

3. Given this GraphQL response:

{"data": {"user": null}, "errors": [{"message": "User not found", "path": ["user"]}]}

What does this response mean?

medium

A. The user exists but has no data.

B. The query failed completely and no data is returned.

C. The server returned a syntax error in the query.

D. Partial data is returned; user field is null due to an error.

Solution

1. Step 1: Analyze the data field

   The data field shows "user": null, meaning no user data was returned.

2. Step 2: Analyze the errors field

   The errors field shows "User not found" with path ["user"], indicating an error related to the user field.

3. Final Answer:

   Partial data is returned; user field is null due to an error. -> Option D

4. Quick Check:

   Partial data + error path = null field [OK]

Hint: Null data with errors means partial failure [OK]

Common Mistakes:

• Assuming no data means full failure
• Ignoring the errors field
• Thinking user exists without data

4. You receive this GraphQL response:

{"data": {"post": {"title": "Hello World"}}, "errors": [{"message": "Author not found", "path": ["post", "author"]}]}

What is the likely issue?

medium

A. The post data is returned but author field caused an error.

B. The server returned no data at all.

C. The entire query failed due to syntax error.

D. The author field is missing from the query.

Solution

1. Step 1: Check the data field

   The data field contains post with a title, so some data is returned.

2. Step 2: Check the errors field

   The error message "Author not found" with path ["post", "author"] shows the error is specific to the author field inside post.

3. Final Answer:

   The post data is returned but author field caused an error. -> Option A

4. Quick Check:

   Data present + error path = partial error [OK]

Hint: Error path shows which field failed [OK]

Common Mistakes:

• Assuming full query failure
• Ignoring error path details
• Thinking missing field means query error

5. Why does GraphQL include the error path in its error messages?

hard

A. To replace HTTP status codes for error classification.

B. To indicate the exact field causing the error for better client handling.

C. To hide sensitive server information from clients.

D. To provide a list of all fields in the query.

Solution

1. Step 1: Understand the purpose of error path

   The path shows the exact location in the query where the error happened.

2. Step 2: Understand client benefit

   This helps clients know which part of the data failed and handle partial data properly.

3. Final Answer:

   To indicate the exact field causing the error for better client handling. -> Option B

4. Quick Check:

   Error path = pinpoint error location [OK]

Hint: Error path points to problem field [OK]

Common Mistakes:

• Thinking path replaces HTTP status codes
• Assuming path hides server info
• Confusing path with full query fields