PATCH for partial updates in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the PATCH method in REST APIs?

PATCH is used to make partial updates to a resource, changing only specified fields without replacing the entire resource.

beginner

How does PATCH differ from PUT in REST APIs?

PUT replaces the entire resource with the new data, while PATCH updates only the specified fields, leaving others unchanged.

beginner

When should you use PATCH instead of PUT?

Use PATCH when you want to update only some fields of a resource without sending the full resource data.

intermediate

What HTTP status code is commonly returned after a successful PATCH request?

A successful PATCH request often returns 200 OK with the updated resource or 204 No Content if no content is returned.

intermediate

Can PATCH requests be idempotent?

PATCH is not necessarily idempotent, but it can be designed to be idempotent depending on the implementation.

Which HTTP method is best for updating only a few fields of a resource?

A POST

B GET

C PATCH

D DELETE

PATCH is designed for partial updates, changing only specified fields.

What is the difference between PUT and PATCH?

A PUT replaces the entire resource; PATCH updates parts of it

B PUT updates parts of the resource; PATCH replaces it

C PUT deletes the resource; PATCH creates a new one

D PUT and PATCH are the same

PUT replaces the whole resource, PATCH updates only specified fields.

Which status code indicates a successful PATCH request with no content returned?

A 200 OK

B 204 No Content

C 201 Created

D 404 Not Found

204 No Content means the request succeeded but no content is returned.

Is PATCH always idempotent?

A Only when used with GET

B No, never

C Yes, always

D It depends on implementation

PATCH can be idempotent if designed that way, but it is not guaranteed.

Which HTTP method should you use to update a resource completely?

A PUT

B OPTIONS

C GET

D PATCH

PUT replaces the entire resource with new data.

Explain the difference between PATCH and PUT methods in REST APIs.

Think about how much data you send and what changes happen.

Describe when and why you would use PATCH for partial updates.

Imagine you only want to change one detail, not everything.

Practice

1. What is the main purpose of using the PATCH method in REST APIs?

easy

A. To update only specific fields of a resource without sending the entire data

B. To create a new resource on the server

C. To delete a resource completely

D. To retrieve data from the server

Solution

1. Step 1: Understand HTTP methods

   HTTP methods like GET, POST, PUT, DELETE, and PATCH have different purposes. PATCH is designed for partial updates.

2. Step 2: Identify PATCH behavior

   PATCH sends only the fields that need to be changed, unlike PUT which requires the full resource data.

3. Final Answer:

   To update only specific fields of a resource without sending the entire data -> Option A

4. Quick Check:

   PATCH updates parts only [OK]

Hint: PATCH updates parts, not whole resource [OK]

Common Mistakes:

• Confusing PATCH with PUT which replaces full resource
• Thinking PATCH creates new resources
• Using PATCH to delete resources

2. Which of the following is the correct way to send a PATCH request to update a user's email using JSON?

easy

A. PATCH /users/123 {"email": "[e-mail]"}

B. PATCH /users/123 {"username": "newuser"}

C. GET /users/123 {"email": "[e-mail]"}

D. DELETE /users/123 {"email": "[e-mail]"}

Solution

1. Step 1: Identify HTTP method and endpoint

   PATCH is used to update part of the resource at /users/123.

2. Step 2: Check JSON body for correct field

   The JSON body contains only the field to update, here "email" with new value.

3. Final Answer:

   PATCH /users/123 {"email": "[e-mail]"} -> Option A

4. Quick Check:

   PATCH + partial JSON body = correct syntax [OK]

Hint: PATCH with only fields to update in JSON body [OK]

Common Mistakes:

• Using GET or DELETE instead of PATCH
• Sending unrelated fields in PATCH body
• Trying to update username when email is asked

3. Given this PATCH request body to update a product:

{"price": 19.99}

What will be the result if the original product data was

{"name": "Book", "price": 25.00, "stock": 10}

?

medium

A. {"name": "Book", "price": 25.00, "stock": 10}

B. {"price": 19.99}

C. {"name": "Book", "price": 19.99, "stock": 10}

D. {"name": "Book", "stock": 10}

Solution

1. Step 1: Understand PATCH partial update

   PATCH updates only the fields sent, here "price" changes to 19.99.

2. Step 2: Combine unchanged fields with updated field

   Fields not in PATCH body remain unchanged, so "name" and "stock" stay the same.

3. Final Answer:

   {"name": "Book", "price": 19.99, "stock": 10} -> Option C

4. Quick Check:

   PATCH updates price only, others unchanged [OK]

Hint: PATCH changes only sent fields, keeps others [OK]

Common Mistakes:

• Replacing entire object instead of partial update
• Removing fields not in PATCH body
• Ignoring updated field in result

4. You send this PATCH request to update a user's profile:

{"email": "[e-mail]", "age": "twenty"}

The server expects age as an integer. What is the likely problem?

medium

A. The PATCH request will succeed and update both fields

B. The server will delete the age field from the user profile

C. The server will ignore the age field and update only email

D. The server will reject the request due to invalid data type for age

Solution

1. Step 1: Check data types in PATCH body

   "age" is sent as string "twenty" but server expects integer.

2. Step 2: Understand server validation

   Most servers validate data types and reject requests with invalid types.

3. Final Answer:

   The server will reject the request due to invalid data type for age -> Option D

4. Quick Check:

   Invalid data type causes rejection [OK]

Hint: Check data types match server expectations [OK]

Common Mistakes:

• Assuming server auto-converts wrong types
• Thinking PATCH ignores invalid fields silently
• Believing PATCH deletes fields on error

5. You have a REST API for managing tasks with fields: title, completed, and priority. You want to mark a task as completed without changing other fields. Which PATCH request body is best?

hard

A. {"title": "", "completed": true, "priority": null}

B. {"completed": true}

C. {"completed": true, "priority": "high"}

D. {"title": "New Task"}

Solution

1. Step 1: Identify minimal update needed

   Only the "completed" field needs to change, so send only that.

2. Step 2: Avoid sending unrelated or empty fields

   Sending empty or null fields may overwrite data unintentionally.

3. Final Answer:

   {"completed": true} -> Option B

4. Quick Check:

   Send only changed fields in PATCH body [OK]

Hint: Send only fields you want to update in PATCH [OK]

Common Mistakes:

• Sending all fields even if unchanged
• Sending empty or null values accidentally
• Using PUT instead of PATCH for partial update