What is PATCH used for?

PATCH is an HTTP method used to partially update a resource on the server.

In simple terms: PATCH is needed to change only part of the data, not the whole object.

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#The main purpose of PATCH

PATCH is used when you need to:

• change one or a few fields of a resource
• leave the rest of the data untouched
• perform a "targeted" update

The typical meaning of PATCH:

"Change these specific fields, leave everything else as is"

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#How PATCH works

1. The client sends an HTTP request with the PATCH method
2. The request body carries only the fields being changed
3. The server:

• finds the resource
• updates only the specified fields

4. The server returns an HTTP response

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#Where data is sent with PATCH

Data is sent:

• in the request body
• usually as JSON

An example of what the request means:

The rest of the resource's fields do not change.

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#PATCH vs PUT (very important)

This is a common interview question.

• PUT
  • a full replacement of the resource
  • the whole object must be sent
  • a missing field may be removed
• PATCH
  • a partial update
  • only the changed fields are sent
  • safer for small changes

A way to remember it:

• PUT - "replace everything"
• PATCH - "fix a piece"

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#Properties of PATCH

• usually not idempotent (depends on the implementation)
• not cached
• used in REST APIs for updates

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#Real-life example

PATCH is like:

• changing a phone number in a profile
• fixing a typo in a text
• updating one setting

You are not rewriting everything, you are changing only what's needed.