Validation error details in Rest API - Step-by-Step Execution

Concept Flow - Validation error details

Receive API Request

↓

Validate Input Data

↓

Process Request

↓

Send Success

↓

End

The API receives a request, checks the input data, and either processes it or returns detailed validation errors.

Execution Sample

Rest API

POST /api/users
{
  "email": "bademail",
  "age": -5
}

An API receives a POST request with invalid email and age fields to demonstrate validation error details.

Execution Table

Step	Validation Check	Condition	Result	Error Detail Collected
1	Check email format	"bademail" contains '@'	False	"email": "Invalid email format"
2	Check age >= 0	-5 >= 0	False	"age": "Must be non-negative"
3	All validations passed?	No	No	Return errors collected
4	Send response	Errors exist	Send 400 Bad Request	{"email": "Invalid email format", "age": "Must be non-negative"}

💡 Validation failed due to invalid email and negative age, so error details are returned.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
errors	{}	{"email": "Invalid email format"}	{"email": "Invalid email format", "age": "Must be non-negative"}	{"email": "Invalid email format", "age": "Must be non-negative"}

Key Moments - 2 Insights

Why do we collect all errors instead of stopping at the first one?

Collecting all errors helps the user fix all issues at once, as shown in steps 1 and 2 where both email and age errors are collected before responding.

What happens if all validations pass?

If all validations pass, the API processes the request and sends a success response instead of error details, which is not shown here but implied after step 3.

Visual Quiz - 3 Questions

Look at the execution table, what error detail is collected at step 1?

A "age": "Must be non-negative"

B "email": "Invalid email format"

C No error collected

D "email": "Missing field"

💡 Hint

Check the 'Error Detail Collected' column at step 1 in the execution table.

At which step does the API decide to send an error response?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look for the step where the response is sent with error details in the execution table.

If the age was 10 instead of -5, how would the errors variable change after step 2?

A {"age": "Must be non-negative"}

B {}

C {"email": "Invalid email format"}

D {"email": "Invalid email format", "age": "Must be non-negative"}

💡 Hint

Refer to variable_tracker and consider that only the email error remains if age is valid.

Concept Snapshot

Validation error details in REST API:
- Receive input data
- Check each field for correctness
- Collect all errors found
- Return errors in response with 400 status
- Helps client fix all issues at once

Full Transcript

This visual trace shows how a REST API handles validation error details. The API receives a request with input data. It checks each field, like email format and age value. If a field is invalid, it adds an error message to a collection. After all checks, if any errors exist, the API sends a 400 Bad Request response with all error details. This approach helps users fix all input problems together instead of one by one.