PUT vs PATCH — which do you use to update a resource, and why does it matter?
⚡ Short Answer
PUT replaces the entire resource (send the full representation) and is idempotent. PATCH applies a partial modification (only changed fields) and isn't necessarily idempotent. Use PUT for full replacement, PATCH for partial updates — and document the PATCH format (merge vs JSON Patch).
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“PUT vs PATCH — which do you use to update a resource, and why does it matter?”
🧠Mind Map Answer
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PUT /users/101 { "name":"John", "email":"j@x.com" } # full
PATCH /users/101 { "email":"new@x.com" } # partial🔥What If?
Think Beyond the Expected
A client sends PUT with only the changed field and other fields get wiped — why?
PUT means 'replace the whole resource' — fields omitted from the body are treated as removed/defaulted. The client either must send the complete representation with PUT, or use PATCH for partial updates. This is a very common API bug.
😂Real World
Accidental data loss from partial PUTs is a frequent API bug; teams standardize on PATCH (often JSON Merge Patch) for edits and reserve PUT for full replacement or upsert.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Using PUT for partial updates (wipes fields)
- ✗Assuming PATCH is always idempotent
- ✗Not documenting the PATCH body format
✅Best Practices
- ✓PATCH for partial edits, PUT for full replace
- ✓Pick and document a PATCH format
- ✓Validate the full body on PUT
🔁Follow-up Questions
- 1Is PATCH idempotent? When is it / isn't it?
- 2JSON Merge Patch vs JSON Patch (RFC 6902)?
- 3Can PUT create a resource (upsert)?
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Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: HTTP Methods (REST APIs) Interview question: "PUT vs PATCH — which do you use to update a resource, and why does it matter?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
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