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What is the difference between PUT and PATCH, and how do you implement PATCH?

Web API & REST HTTP Intermediate 2–3 Yrs3–5 Yrs Conceptual 1 min read

Quick Answer

PUT replaces the whole resource — you send the complete representation, and it's idempotent. PATCH applies a partial update — you send only the changes. Two formats: JSON Merge Patch (send a partial object) and JSON Patch (RFC 6902 — an array of operations like replace /name).

PUT means “here is the entire new state of this resource” — you send everything and it overwrites, which makes it idempotent. PATCH is a partial update — you send just what changed. There are two flavours: merge patch, where you send a partial JSON object, and JSON Patch, which is a list of operations like “replace the name field.” In ASP.NET Core I take a JsonPatchDocument<T>, apply it to a DTO, and then validate. One thing to note is PATCH isn't automatically idempotent — an add operation appends every time — so I design the operations carefully.

  • ASP.NET Core: [HttpPatch] public IActionResult Patch(int id, [FromBody] JsonPatchDocument<CustomerDto> patch) — apply with patch.ApplyTo(dto, ModelState), then validate.
  • JSON Patch needs AddNewtonsoftJson() in current ASP.NET Core.
  • Merge patch is simpler for clients but can't express “set this field to null” unambiguously.
  • PATCH isn't guaranteed idempotent (an add op appends each time); design your ops to be idempotent if you want safe retries.
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