Nested error reporting in Rest API - Step-by-Step Execution

Concept Flow - Nested error reporting

Receive API Request

↓

Validate Outer Data

↓

Validate Inner Data

↓

Process Request

↓

Return Success Response

The API receives a request, validates outer data first, then inner data if outer is valid, and returns errors nested inside the response if any validation fails.

Execution Sample

Rest API

POST /api/data
{
  "user": {"id": 123, "name": ""}
}

Response: {
  "error": {
    "user": {
      "name": "Name cannot be empty"
    }
  }
}

This example shows a POST request with nested user data where the inner 'name' field is empty, triggering a nested error response.

Execution Table

Step	Action	Check	Result	Next Step
1	Receive API request	N/A	Request data received	Validate outer data
2	Validate outer data	Is 'user' present?	Yes	Validate inner data
3	Validate inner data	Is 'user.id' valid?	Yes	Check 'user.name'
4	Validate inner data	Is 'user.name' non-empty?	No	Return nested error for 'user.name'
5	Return nested error	N/A	{"error":{"user":{"name":"Name cannot be empty"}}}	End
6	End	N/A	Response sent with nested error	Stop

💡 Validation failed at inner 'user.name', so nested error response is returned.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
request_data	{}	{"user":{"id":123,"name":""}}	{"user":{"id":123,"name":""}}	{"user":{"id":123,"name":""}}	{"user":{"id":123,"name":""}}
error_response	null	null	null	{"error":{"user":{"name":"Name cannot be empty"}}}	{"error":{"user":{"name":"Name cannot be empty"}}}

Key Moments - 2 Insights

Why does the error appear nested inside 'user' instead of at the top level?

Because the validation checks inner fields, errors are grouped inside the related object to clearly show which part failed, as shown in step 5 of the execution_table.

What happens if the outer 'user' field is missing?

The validation stops early and returns an outer error immediately, skipping inner checks, as shown in step 2 branching to error in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the inner 'user.name' field checked?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'Check' column for 'Is user.name non-empty?' in the execution_table.

According to variable_tracker, what is the value of 'error_response' after step 3?

A null

B {"error":{"user":{"name":"Name cannot be empty"}}}

C {}

D {"user":{"id":123,"name":""}}

💡 Hint

Look at the 'error_response' row under 'After Step 3' in variable_tracker.

If 'user.name' was valid, what would be the next step after step 4 in execution_table?

A Return nested error

B Return outer error

C Process request

D End

💡 Hint

Refer to the concept_flow where successful inner validation leads to processing the request.

Concept Snapshot

Nested error reporting in REST APIs:
- Validate outer data first.
- If outer valid, validate inner data.
- Return errors nested inside related fields.
- Helps clients know exactly where errors are.
- Stops validation early on outer errors.

Full Transcript

This visual execution shows how nested error reporting works in a REST API. The API receives a request with nested data. It first checks the outer data, like if the 'user' object exists. If that passes, it checks inner fields like 'user.id' and 'user.name'. If an inner field is invalid, it returns an error nested inside the related object, for example, an error inside 'user' for the 'name' field. The execution table traces each step, showing checks and results. The variable tracker shows how the request data and error response change. Key moments clarify why errors are nested and what happens if outer data is missing. The quiz tests understanding of when checks happen and how errors are structured. This helps beginners see exactly how nested error reporting flows in an API.