Composite operations (multi-resource) in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this composite REST API call?

Consider a REST API that supports batch requests to create multiple resources in one call. The batch request payload is:

{"operations": [{"method": "POST", "path": "/users", "body": {"name": "Alice"}}, {"method": "POST", "path": "/orders", "body": {"userId": 1, "product": "Book"}}]}

If the API returns the following response, what is the value of response.operations[1].status?

{"operations": [{"status": 201, "body": {"id": 1, "name": "Alice"}}, {"status": 201, "body": {"id": 101, "userId": 1, "product": "Book"}}]}

A 400

B 201

C 404

D 500

💡 Hint

Look at the status code for the second operation in the response.

The second operation in the batch creates an order and returns status 201, which means 'Created'.

🧠 Conceptual

intermediate

Which statement best describes composite operations in REST APIs?

Composite operations allow clients to:

A Cache responses locally to avoid repeated API calls.

B Execute only one resource operation per HTTP request to ensure atomicity.

C Send multiple related requests in a single HTTP call to reduce network overhead.

D Use WebSockets instead of HTTP for faster communication.

💡 Hint

Think about how composite operations improve efficiency.

Composite operations bundle multiple related resource operations into one HTTP request, reducing network overhead and latency.

🔧 Debug

advanced

Identify the error in this composite operation request payload

Given this JSON payload for a composite REST API call:

{"operations": [{"method": "POST", "path": "/users", "body": {"name": "Bob"}}, {"method": "POST", "path": "/orders", "body": {"userId": "abc", "product": "Pen"}}]}

What error will the API most likely return?

A 400 Bad Request due to invalid userId type

B 404 Not Found because /orders path is incorrect

C 500 Internal Server Error due to server crash

D 201 Created for both operations

💡 Hint

Check the data type of userId in the second operation.

The userId should be a numeric ID, but "abc" is a string, causing a validation error and 400 Bad Request.

🚀 Application

advanced

How to ensure atomicity in composite REST API operations?

You want to create a composite operation that either completes all resource creations or none (all-or-nothing). Which approach is best?

A Use a transaction mechanism on the server that rolls back all changes if any operation fails.

B Send operations sequentially and ignore failures in intermediate steps.

C Send all operations in parallel without rollback support.

D Use client-side retries to fix failed operations after the batch completes.

💡 Hint

Atomicity means all succeed or all fail together.

Server-side transactions ensure that if any operation in the batch fails, all changes are undone, preserving atomicity.

❓ Predict Output

expert

What is the final state after this composite operation with dependencies?

Consider a composite REST API call with two operations:

{"operations": [{"id": "op1", "method": "POST", "path": "/projects", "body": {"name": "ProjectX"}}, {"id": "op2", "method": "POST", "path": "/tasks", "body": {"projectId": "${op1.body.id}", "title": "Task1"}}]}

If the server processes these operations and returns:

{"operations": [{"id": "op1", "status": 201, "body": {"id": 42, "name": "ProjectX"}}, {"id": "op2", "status": 201, "body": {"id": 101, "projectId": 42, "title": "Task1"}}]}

What is the value of response.operations[1].body.projectId?

A null

B "${op1.body.id}"

C 101

D 42

💡 Hint

Check how the second operation uses the first operation's result.

The second operation references the first operation's created project ID (42) dynamically, so the projectId is 42.