什么是 CRUD
What is CRUD
一句话：Create / Read / Update / Delete —— 数据操作的四种基本类型。 REST 把它们映射到 HTTP 方法。
| 操作 | 方法 | 路径 | 成功状态码 |
|---|---|---|---|
| Create | POST | /orders | 201 Created |
| Read（列表） | GET | /orders | 200 |
| Read（单个） | GET | /orders/:id | 200，没有则 404 |
| Update（整体） | PUT | /orders/:id | 200 |
| Update（部分） | PATCH | /orders/:id | 200 |
| Delete | DELETE | /orders/:id | 204 No Content |
两个高频追问：
① PUT vs PATCH。PUT 是整体替换—— 没传的字段应该被清空；PATCH 是局部更新—— 只改传了的字段。实践中很多人把 PUT 当 PATCH 用， 这是错的，但要知道现实如此。
② 幂等性。同一个请求发多次，结果一样就叫幂等。
GET/PUT/DELETE——幂等POST——不幂等（发两次会创建两条）PATCH——看实现（{ n: 5 }幂等，{ n: { $inc: 1 } }不幂等）
为什么重要：客户端重试、 网关超时重发时， 幂等的接口是安全的，POST 需要幂等键（idempotency key）来防重复下单。
再一个追问：「删一个不存在的资源返回什么？」——可以是 204 也可以是 404。 返 204 更符合幂等语义 （「删完了」这个结果达成了）； 返 404 信息更明确。关键是团队内一致， 并且写进接口文档。
In one line: Create / Read / Update / Delete — the four basic things you do to data. REST maps them onto HTTP methods.
| Operation | Method | Path | Status on success |
|---|---|---|---|
| Create | POST | /orders | 201 Created |
| Read (list) | GET | /orders | 200 |
| Read (one) | GET | /orders/:id | 200, or 404 if it is not there |
| Update (whole) | PUT | /orders/:id | 200 |
| Update (partial) | PATCH | /orders/:id | 200 |
| Delete | DELETE | /orders/:id | 204 No Content |
Two follow-ups they almost always ask:
① PUT vs PATCH. PUT is a full replacement — fields you leave out should be cleared. PATCH is a partial update — only the fields you send change. Plenty of real code uses PUT as if it were PATCH, which is wrong, but know that it happens.
② Idempotency. Send the same request more than once, get the same result — that is idempotent.
GET/PUT/DELETE— idempotentPOST— not idempotent (send it twice and you get two records)PATCH— depends on the payload ({ n: 5 }is idempotent,{ n: { $inc: 1 } }is not)
Why it matters: when a client retries or a gateway resends after a timeout, an idempotent endpoint is safe. POST needs an idempotency key to stop the same order being placed twice.
One more follow-up: “What do you return when deleting something that does not exist?” — 204 or 404, both defensible. 204 fits the idempotent reading (the outcome you asked for is true); 404 tells the caller more. What matters is that the team agrees and it is in the API docs.