Error response structure in Rest API - Mini Project: Build & Apply

Error Response Structure in REST API

📖 Scenario: You are building a REST API that needs to send clear error messages to clients when something goes wrong. This helps users understand what happened and how to fix it.

🎯 Goal: Create a simple error response structure in JSON format that includes an error code, a message, and details.

📋 What You'll Learn

Create a dictionary called error_response with keys code, message, and details

Set code to the integer 404

Set message to the string "Resource not found"

Set details to a list containing the string "The requested item does not exist"

Print the error_response dictionary as a JSON string

💡 Why This Matters

🌍 Real World

APIs need to send clear error messages so users and developers understand what went wrong and how to fix it.

💼 Career

Knowing how to structure and send error responses is important for backend developers and API designers.

1

Create the error response dictionary

Create a dictionary called error_response with these exact entries: code set to 404, message set to "Resource not found", and details set to a list containing "The requested item does not exist".

Rest API

# Create the error_response dictionary with code, message, and details
# Your code here

Hint

Use curly braces {} to create a dictionary. The details value should be a list with one string inside.

2

Import the JSON module

Import the json module to convert the dictionary to a JSON string.

Rest API

error_response = {
    "code": 404,
    "message": "Resource not found",
    "details": ["The requested item does not exist"]
}

# Import the json module
# Your code here

Hint

Use import json at the top of your code.

3

Convert the dictionary to a JSON string

Use json.dumps() to convert the error_response dictionary to a JSON string and store it in a variable called json_error.

Rest API

import json

error_response = {
    "code": 404,
    "message": "Resource not found",
    "details": ["The requested item does not exist"]
}

# Convert error_response to JSON string and store in json_error
# Your code here

Hint

Use json.dumps(error_response) to convert the dictionary.

4

Print the JSON error response

Print the variable json_error to display the JSON string of the error response.

Rest API

import json

error_response = {
    "code": 404,
    "message": "Resource not found",
    "details": ["The requested item does not exist"]
}

json_error = json.dumps(error_response)

# Print the JSON error response
# Your code here

Hint

Use print(json_error) to show the JSON string.

Practice

1. What is the main purpose of an error response structure in a REST API?

easy

A. To clearly communicate what went wrong during a request

B. To speed up the API response time

C. To store user data securely

D. To format the successful response data

Solution

1. Step 1: Understand the role of error responses

   Error responses are sent when something goes wrong to inform the user or client about the issue.

2. Step 2: Identify the purpose of the error structure

   The structure helps communicate the problem clearly, usually with a code and message.

3. Final Answer:

   To clearly communicate what went wrong during a request -> Option A

4. Quick Check:

   Error response = clear problem message [OK]

Hint: Error responses explain problems clearly to users [OK]

Common Mistakes:

• Thinking error responses speed up API
• Confusing error response with data storage
• Assuming error response formats success data

2. Which of the following is the correct JSON syntax for a simple error response with code 404 and message "Not Found"?

easy

A. {"error": {code: 404, message: "Not Found"}}

B. {"error": {"code": 404, "message": "Not Found"}}

C. {"error": {"code": "404", "message": Not Found}}

D. {"error": {"code": 404, message: Not Found}}

Solution

1. Step 1: Check JSON key and string syntax

   Keys and string values must be in double quotes. Numbers like 404 do not need quotes.

2. Step 2: Identify the correct option

   {"error": {"code": 404, "message": "Not Found"}} uses correct quotes for keys and strings, and number 404 without quotes.

3. Final Answer:

   {"error": {"code": 404, "message": "Not Found"}} -> Option B

4. Quick Check:

   JSON keys and strings need double quotes [OK]

Hint: Use double quotes for keys and string values in JSON [OK]

Common Mistakes:

• Missing quotes around keys
• Using quotes around numbers
• Not quoting string values

3. Given this error response JSON:

{"error": {"code": 401, "message": "Unauthorized access"}}

What is the value of the message field?

medium

A. "error"

B. 401

C. null

D. "Unauthorized access"

Solution

1. Step 1: Locate the message field in the JSON

   The message field is inside the error object and has the value "Unauthorized access".

2. Step 2: Confirm the value type

   The value is a string, so it includes the quotes in JSON representation.

3. Final Answer:

   "Unauthorized access" -> Option D

4. Quick Check:

   message field value = "Unauthorized access" [OK]

Hint: Look inside error object for message value [OK]

Common Mistakes:

• Confusing code with message
• Selecting the key name instead of value
• Assuming null when field exists

4. You receive this error response from your API:

{"error": {"code": "400", "message": "Bad Request"}}

Why might this cause problems in your client code expecting code as a number?

medium

A. Because the error key is misspelled

B. Because the message is missing

C. Because the code is a string, not a number, causing type errors

D. Because the JSON is invalid

Solution

1. Step 1: Identify the data type of code field

   The code field is given as a string "400" instead of a number 400.

2. Step 2: Understand client expectations

   If client expects a number, receiving a string can cause type errors or failed comparisons.

3. Final Answer:

   Because the code is a string, not a number, causing type errors -> Option C

4. Quick Check:

   Type mismatch in code field causes errors [OK]

Hint: Check if code is number, not string, to avoid type errors [OK]

Common Mistakes:

• Ignoring type differences
• Assuming message is missing
• Thinking JSON is invalid

5. You want to design an error response structure that includes an error code, a message, and optionally a list of field errors for validation issues. Which JSON structure below correctly supports this?

hard

A. {"error": {"code": 422, "message": "Validation failed", "fields": [{"field": "email", "error": "Invalid format"}]}}

B. {"error": {"code": 422, "message": "Validation failed", "fields": "email: Invalid format"}}

C. {"error": {"code": 422, "message": "Validation failed", "fields": {"email": "Invalid format"}}}

D. {"error": {"code": 422, "message": "Validation failed", "fields": ["email", "Invalid format"]}}

Solution

1. Step 1: Understand the need for multiple field errors

   We want a list of objects, each with a field name and its error message.

2. Step 2: Check each option's fields format

   {"error": {"code": 422, "message": "Validation failed", "fields": [{"field": "email", "error": "Invalid format"}]}} uses an array of objects with field and error keys, which is clear and extensible.

3. Step 3: Identify why others are incorrect

   {"error": {"code": 422, "message": "Validation failed", "fields": "email: Invalid format"}} uses a string instead of structured data; {"error": {"code": 422, "message": "Validation failed", "fields": {"email": "Invalid format"}}} uses an object but not a list; {"error": {"code": 422, "message": "Validation failed", "fields": ["email", "Invalid format"]}} uses a list mixing field and message without keys.

4. Final Answer:

   {"error": {"code": 422, "message": "Validation failed", "fields": [{"field": "email", "error": "Invalid format"}]}} -> Option A

5. Quick Check:

   Use array of objects for detailed field errors [OK]

Hint: Use array of objects for multiple field errors [OK]

Common Mistakes:

• Using plain strings instead of structured objects
• Mixing field names and messages in arrays without keys
• Using object instead of list for multiple errors