Validation error details in Rest API - Mini Project: Build & Apply

Validation error details

📖 Scenario: You are building a simple REST API that accepts user data. You want to check if the data is valid and show clear error messages when it is not.

🎯 Goal: Create a Python dictionary with user data, set a validation rule, check the data against the rule, and print detailed error messages if the data is invalid.

📋 What You'll Learn

Create a dictionary called user_data with keys name and age and exact values 'Alice' and 17

Create a variable called min_age and set it to 18

Use an if statement to check if user_data['age'] is less than min_age and create an error message string called error_message

Print the error_message string

💡 Why This Matters

🌍 Real World

APIs often need to check if user input is correct and show clear error messages to help users fix mistakes.

💼 Career

Understanding validation and error messages is important for backend developers, API designers, and anyone working with user input.

1

Create user data dictionary

Create a dictionary called user_data with keys 'name' and 'age' and values 'Alice' and 17 exactly.

Rest API

# Create the user_data dictionary with name 'Alice' and age 17
# Your code here

Hint

Use curly braces to create a dictionary. Keys are strings and values are 'Alice' and 17.

2

Set minimum age for validation

Create a variable called min_age and set it to the integer 18.

Rest API

user_data = {'name': 'Alice', 'age': 17}
# Create min_age variable and set it to 18
# Your code here

Hint

Just assign 18 to the variable min_age.

3

Check age and create error message

Use an if statement to check if user_data['age'] is less than min_age. If true, create a string variable called error_message with the text 'User is too young: age is X' where X is the actual age from user_data.

Rest API

user_data = {'name': 'Alice', 'age': 17}
min_age = 18
# Check age and create error_message if age is less than min_age
# Your code here

Hint

Use an if statement and an f-string to include the age in the message.

4

Print the error message

Print the variable error_message to show the validation error details.

Rest API

user_data = {'name': 'Alice', 'age': 17}
min_age = 18
if user_data['age'] < min_age:
    error_message = f"User is too young: age is {user_data['age']}"
# Print the error_message
# Your code here

Hint

Use print(error_message) inside the if block.

Practice

1. What is the main purpose of validation error details in a REST API response?

easy

A. To explain which input fields are wrong and why

B. To speed up the server response time

C. To encrypt the data sent to the client

D. To log user activity for analytics

Solution

1. Step 1: Understand validation errors

   Validation errors tell us what input data is incorrect or missing.

2. Step 2: Purpose of error details

   Error details explain which fields caused the problem and why, helping fix input.

3. Final Answer:

   To explain which input fields are wrong and why -> Option A

4. Quick Check:

   Validation error details = Explain input errors [OK]

Hint: Validation errors show what and why input is wrong [OK]

Common Mistakes:

• Thinking error details speed up server
• Confusing error details with encryption
• Assuming error details are for logging only

2. Which of the following is the correct JSON structure for validation error details in a REST API?

easy

A. {"data": {"email": "[e-mail]"}}

B. ["email", "password"]

C. {"status": 200, "message": "Success"}

D. {"errors": {"email": "Invalid format", "password": "Too short"}}

Solution

1. Step 1: Identify error details format

   Error details usually use a JSON object with field names as keys and error messages as values.

2. Step 2: Check options

   {"errors": {"email": "Invalid format", "password": "Too short"}} shows a JSON object with "errors" key and field-specific messages, which is correct.

3. Final Answer:

   {"errors": {"email": "Invalid format", "password": "Too short"}} -> Option D

4. Quick Check:

   Validation errors = JSON object with field messages [OK]

Hint: Look for JSON object with field names and error messages [OK]

Common Mistakes:

• Using arrays instead of objects for errors
• Confusing success response with error details
• Missing field names in error messages

3. Given this JSON error response:

{"errors": {"username": "Required field", "age": "Must be a number"}}

What message should the client show for the 'age' field?

medium

A. Must be a number

B. Invalid email format

C. Required field

D. Password too short

Solution

1. Step 1: Read the JSON error response

   The error for "age" is "Must be a number".

2. Step 2: Match the message to the field

   The client should show the message exactly as given for the "age" field.

3. Final Answer:

   Must be a number -> Option A

4. Quick Check:

   Field 'age' error = Must be a number [OK]

Hint: Match field name to its error message in JSON [OK]

Common Mistakes:

• Mixing error messages between fields
• Showing unrelated error messages
• Ignoring the JSON structure

4. You receive this validation error JSON:

{"error": "Invalid input", "fields": ["email", "password"]}

What is wrong with this error detail format?

medium

A. It correctly shows error details

B. It uses a list instead of mapping fields to messages

C. It uses wrong HTTP status code

D. It encrypts error messages

Solution

1. Step 1: Analyze error detail format

   The "fields" key has a list of field names but no messages explaining the errors.

2. Step 2: Identify correct format

   Validation error details should map each field to a specific error message, not just list fields.

3. Final Answer:

   It uses a list instead of mapping fields to messages -> Option B

4. Quick Check:

   Error details need field-message pairs [OK]

Hint: Error details need field names paired with messages [OK]

Common Mistakes:

• Listing fields without error explanations
• Assuming any error JSON is correct
• Ignoring the need for descriptive messages

5. You want to design a REST API validation error response that shows multiple errors per field. Which JSON structure correctly supports this?

hard

A. {"errors": ["email: Required", "password: Too short"]}

B. {"error": "Multiple errors found"}

C. {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}}

D. {"fields": ["email", "password"]}

Solution

1. Step 1: Understand multiple errors per field

   To show many errors for one field, use a list (array) of messages for that field.

2. Step 2: Check JSON structures

   {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}} uses a dictionary with field keys and lists of error messages, which fits the need.

3. Final Answer:

   {"errors": {"email": ["Required", "Invalid format"], "password": ["Too short"]}} -> Option C

4. Quick Check:

   Multiple errors per field = list of messages [OK]

Hint: Use lists inside error fields to show multiple messages [OK]

Common Mistakes:

• Using flat lists without field keys
• Not supporting multiple messages per field
• Using vague error messages without details