Understanding PUT vs PATCH in RESTful APIs: Practical Use Cases and Differences

Introduction

In the world of RESTful APIs, understanding how to manipulate resources is crucial for both developers and API consumers. Two HTTP methods that are often used for updating resources are PUT and PATCH. While they might seem similar at first glance, they serve distinct purposes and have different implications in terms of idempotency and resource manipulation.

Defining PUT and PATCH

PUT Method

The PUT method is designed to update a resource entirely. According to RFC 2616, when you issue a PUT request, the server stores or updates the entire entity under the specified URI. If the resource exists, it is replaced; if not, a new resource is created.

Idempotency: PUT requests are idempotent, meaning that making multiple identical requests has the same effect as making a single request. This characteristic ensures consistency and reliability in operations involving resource updates.

PATCH Method

The PATCH method, defined in RFC 5789, allows for partial modifications of a resource. It applies a set of changes to the target resource, which can be useful when only certain fields need updating.

Idempotency: PATCH requests can also be idempotent if designed correctly. Each request should result in the same state after application, even if repeated multiple times.

Practical Differences and Use Cases

When to Use PUT

Complete Resource Replacement: Use PUT when you have all the details of a resource and intend to replace it entirely.
Idempotency Requirement: If your operation must be idempotent, PUT is a suitable choice. This is particularly important in scenarios where operations might be repeated due to network retries or other factors.

Example Scenario:

PUT /users/1
{
  "name": "Sam Kwee",
  "email": "[email protected]",
  "address": "123 Mockingbird Lane",
  "city": "New York",
  "state": "NY",
  "zip": "10001"
}

In this example, the entire user resource is replaced with new data.

When to Use PATCH

Partial Updates: Use PATCH when you need to update only specific fields of a resource without altering others.
Efficiency: It can be more efficient than PUT as it requires less bandwidth and processing power by sending only the changes rather than the entire resource.

Example Scenario:

PATCH /users/1
{
  "email": "[email protected]"
}

Here, only the email field is updated for user with ID 1.

Idempotency in Practice

PUT and Idempotency

A PUT request remains idempotent as long as it replaces a resource entirely. Repeated requests result in no additional changes beyond the first application.

Example of Non-Idempotent Use:

PUT /users/1
{
  "email": "[email protected]"
}

If name, address, and other fields are omitted, they could be lost with repeated requests, violating idempotency.

PATCH and Idempotency

A PATCH request can be idempotent if it consistently results in the same resource state. This is achieved by ensuring that each patch operation’s effect does not depend on its frequency or previous states.

Example of Idempotent PATCH:

PATCH /users/1
{
  "email": "[email protected]"
}

Reapplying this patch will consistently set the email to [email protected].

Conclusion

Choosing between PUT and PATCH depends on the specific requirements of your API operation. Use PUT for full resource replacements where idempotency is critical, and use PATCH for efficient partial updates. Understanding these distinctions will help you design more robust and reliable APIs.