Why PUT for full replacement in Rest API? - Purpose & Use Cases

The Big Idea

What if you could update everything at once without missing a single detail?

The Scenario

Imagine you have a list of user profiles stored in a system. You want to update a user's information completely, like changing their name, email, and address all at once. Doing this manually means you have to check each field, remove old data, and add new data piece by piece.

The Problem

This manual approach is slow and risky. You might forget to update some fields or accidentally leave old data behind. It's like trying to replace all the ingredients in a recipe one by one without making a mess or missing anything.

The Solution

The PUT method in REST APIs solves this by letting you send the full new version of the resource. The server then replaces the old resource completely with the new one you provide. This makes updates clear, simple, and less error-prone.

Before vs After

✗ Before

PATCH /users/123 { "email": "[e-mail]" } // update one field manually

✓ After

PUT /users/123 { "name": "New Name", "email": "[e-mail]", "address": "New Address" } // replace entire user data

What It Enables

It enables you to update entire resources in one clear action, ensuring data stays consistent and complete.

Real Life Example

When a user edits their profile page and submits all changes at once, the system uses PUT to replace the old profile with the new one, avoiding partial updates or leftover old data.

Key Takeaways

Manual updates can be slow and error-prone.

PUT replaces the whole resource in one step.

This keeps data consistent and easier to manage.

Practice

1. What does the HTTP PUT method do when used on a REST API resource URL?

easy

A. Retrieves the resource data from the URL

B. Partially updates the resource fields at the URL

C. Fully replaces the resource at the URL with the provided data

D. Deletes the resource at the URL

Solution

1. Step 1: Understand PUT method purpose

   PUT is designed to replace the entire resource at the given URL with the data sent in the request.

2. Step 2: Compare with other methods

   Unlike PATCH which updates partially, PUT replaces fully. GET retrieves, DELETE removes.

3. Final Answer:

   Fully replaces the resource at the URL with the provided data -> Option C

4. Quick Check:

   PUT = full replacement [OK]

Hint: PUT replaces entire resource, not partial update [OK]

Common Mistakes:

• Confusing PUT with PATCH partial update
• Thinking PUT deletes resource
• Assuming PUT only retrieves data

2. Which of the following is the correct HTTP method and usage to fully replace a resource at URL /users/123 with new data in JSON format?

easy

A. POST /users/123 with JSON body

B. PUT /users/123 with JSON body

C. PATCH /users/123 with JSON body

D. GET /users/123 with JSON body

Solution

1. Step 1: Identify method for full replacement

   PUT is the HTTP method used to fully replace a resource at a specific URL.

2. Step 2: Match method with URL and body

   PUT /users/123 with JSON body replaces the user data fully. POST is for creation, PATCH partial update, GET retrieves.

3. Final Answer:

   PUT /users/123 with JSON body -> Option B

4. Quick Check:

   PUT + URL + JSON = full replace [OK]

Hint: Use PUT with URL and full JSON body to replace resource [OK]

Common Mistakes:

• Using POST instead of PUT for replacement
• Using PATCH for full replacement
• Sending body with GET request

3. Given a REST API with a user resource at /users/42 initially having data {"name": "Alice", "age": 30}, what will be the resource data after this PUT request?

PUT /users/42
{"name": "Bob"}

medium

A. {"name": "Bob"}

B. {"name": "Bob", "age": 30}

C. {"age": 30}

D. Resource deleted

Solution

1. Step 1: Understand PUT replaces entire resource

   The PUT request replaces the whole resource data with the new JSON body, removing any fields not included.

2. Step 2: Apply replacement to given data

   Original data had name and age, but PUT body only has name "Bob", so age is removed.

3. Final Answer:

   {"name": "Bob"} -> Option A

4. Quick Check:

   PUT replaces all fields, missing fields removed [OK]

Hint: PUT replaces all fields; missing fields are removed [OK]

Common Mistakes:

• Assuming PUT merges fields like PATCH
• Expecting old fields to remain if not sent
• Thinking PUT deletes resource

4. You wrote this PUT request to update a resource:

PUT /items/10
{"price": 100}

But after sending, the resource lost all other fields except price. How can you fix this to keep other fields intact?

medium

A. Use GET method instead

B. Add missing fields to the PUT JSON body

C. Send an empty body with PUT

D. Change PUT to PATCH to update partially

Solution

1. Step 1: Identify cause of lost fields

   PUT replaces the entire resource, so missing fields in body are removed.

2. Step 2: Choose method to update partially

   PATCH updates only specified fields, keeping others intact.

3. Final Answer:

   Change PUT to PATCH to update partially -> Option D

4. Quick Check:

   PATCH = partial update, keeps other fields [OK]

Hint: Use PATCH for partial update, PUT replaces all [OK]

Common Mistakes:

• Trying to fix by adding missing fields manually
• Sending empty body with PUT
• Using GET to update resource

5. You want to update a user resource at /users/77 with new data {"name": "Eve", "age": 28}. The resource may or may not exist. Which is the best approach using PUT to ensure the resource is created if missing or fully replaced if exists?

hard

A. Send a PUT request with full user data to /users/77

B. Send a POST request to /users with partial data

C. Send a PATCH request to /users/77 with partial data

D. Send a GET request to /users/77 before updating

Solution

1. Step 1: Understand PUT behavior for create or replace

   PUT can create the resource if it does not exist, or fully replace it if it does.

2. Step 2: Apply PUT with full data to target URL

   Sending PUT with full user data to /users/77 ensures creation or full replacement.

3. Final Answer:

   Send a PUT request with full user data to /users/77 -> Option A

4. Quick Check:

   PUT = create or replace resource fully [OK]

Hint: PUT creates or replaces resource at URL with full data [OK]

Common Mistakes:

• Using POST which creates new resource with new ID
• Using PATCH which only updates existing resource partially
• Using GET before update unnecessarily