根据微软:控制器动作返回类型在ASP。NET Core web API，向下滚动几乎到底部，你会发现下面关于404的简介，与数据库中没有的对象有关。在这里，他们建议404适用于空数据。

Just an addition from a developer that struggled many times with this situation. As you might have noticed it is always a discussion whether you return a 404 or 200 or 204 when a particular resource does not exist. The discussion above shows that this topic is pretty confusing and opinion based ( while there is a http-status-code standard existing ). I personally recommend, as it was not mentioned yet I guess, no matter how you decide DOCUMENT IT IN YOUR API-DEFINITION. Of course a client-side developer has in mind when he/she uses your particular "REST"- api to use his/her knowledge about Rest and expects that your api works this way. I guess you see the trap. Therefor I use a readme where I explicitly define in which cases I use which status code. This doesn't mean that I use some random definion. I always try to use the standard but to avoid such cases I document my usage. The client might think you are wrong in some specific cases but as it is documented, there is no need for additional discussions what saves time for you and the developer.

One sentence to the Ops question: 404 is a code that always comes in my mind when I think back about starting to develop backend-applications and I configured something wrong in my controller-route so that my Controller method is not called. With that in mind, I think if the request does reach your code in a Controller method, the client did a valid request and the request endpoint was found. So this is an indication not to use 404. If the db query returns not found, I return 200 but with an empty body.

起初，我认为204是有意义的，但经过讨论，我相信404是唯一真正正确的回答。考虑以下数据:

用户:约翰，彼得

METHOD  URL                      STATUS  RESPONSE
GET     /users                   200     [John, Peter]
GET     /users/john              200     John
GET     /unknown-url-egaer       404     Not Found
GET     /users/kyle              404     User Not found
GET     /users?name=kyle`        200     []
DELETE  /users/john              204     No Content

背景知识:

the search returns an array, it just didn't have any matches but it has content: an empty array. 404 is of course best known for url's that aren't supported by the requested server, but a missing resource is in fact the same. Even though /users/:name is matched with users/kyle, the user Kyle is not available resource so a 404 still applies. It isn't a search query, it is a direct reference by a dynamic url, so 404 it is. After suggestions in the comments, customizing the message of the 404 is another way of helping out the API consumer to even better distinguish between complete unknown routes and missing entities.

不管怎样，我的意见。

这个话题中的答案(在撰写本文时已经有26个)完美地说明了开发人员理解他们正在使用的构造的语义是多么重要。

如果不理解这一点，那么响应状态代码是响应的属性而不是其他属性就不明显了。这些代码存在于响应的上下文中，它们在此上下文中之外的含义是未定义的。

响应本身就是请求的结果。请求对资源进行操作。资源、请求、响应和状态代码是HTTP的结构，就HTTP而言:

HTTP提供了与资源(第2节)交互的统一接口，无论其类型、性质或实现如何，通过操作和传输表示(第3节)。

换句话说，响应状态码的范围受到一个接口的限制，该接口只关心一些目标资源，并处理用于与这些资源交互的消息。服务器应用程序逻辑超出了范围，您使用的数据也不重要。

当使用HTTP时，它总是与资源一起使用。资源被以太转移或操纵。在任何情况下，除非我们在量子世界中，资源要么存在要么不存在，不存在第三种状态。

如果发出HTTP请求来获取(传输)资源的表示(如本问题中所示)，而资源不存在，则响应结果应该显示一个带有相应404代码的失败。目标-获取表示-没有达到，资源没有找到。在HTTP上下文中不应该有对结果的其他解释。

RFC 7231超文本传输协议(HTTP/1.1):语义和内容，在这里多次提到，但主要是作为状态码描述的参考。我强烈建议通读整个文档，而不仅仅是第6节，以便更好地理解HTTP接口及其组件的作用域和语义。

在以前的项目中，我使用了404。如果没有用户9，则没有找到对象。因此404 Not Found是合适的。

如果对象存在，但没有数据，则为204 no Content。我认为在你的例子中，这个物体并不存在。

TL;DR:使用404

请看这个博客。这解释得很好。

博客对204的评论总结如下:

204 No Content作为浏览器的响应代码并不是特别有用(尽管根据HTTP规范，浏览器需要将其理解为“不要更改视图”的响应代码)。 然而，No Content对于ajax web服务非常有用，它可能想要表示成功而不需要返回任何东西。(特别是在DELETE或post这样不需要反馈的情况下)。

因此，您的问题的答案是在您的情况下使用404。204是一个专门的响应代码，您不应该经常将其返回给浏览器以响应GET。

其他响应代码甚至比204和404更不合适:

200 should be returned with the body of whatever you successfully fetched. Not appropriate when the entity you're fetching doesn't exist. 202 is used when the server has begun work on an object but the object isn't fully ready yet. Certainly not the case here. You haven't begun, nor will you begin, construction of user 9 in response to a GET request. That breaks all sorts of rules. 400 is used in response to a poorly formatted HTTP request (for instance malformed http headers, incorrectly ordered segments, etc). This will almost certainly be handled by whatever framework you're using. You shouldn't have to deal with this unless you're writing your own server from scratch. Edit: Newer RFCs now allow for 400 to be used for semantically invalid requests.

维基百科对HTTP状态码的描述尤其有用。 您也可以在www.w3.org上看到HTTP/1.1 RFC2616文档中的定义