The RESTful flow?

问题:

So...

I've been reading about REST a little bit, and the idea behind it sounds nice, but the question is, can it be easily integrated into the standard flow of a webpage?

For example, a user creates some sort of item, a blog post or what have you, and now he wants to delete it, so he clicks a 'delete' link on the page. Now what? How do we issue a DELETE request to, say, http://mysite.com/posts/5? And how do we handle that request? I have no experience with cURL or anything, but from the looks of it, I would have to curl_init('http://mysite.com/posts/5') and then work some magic. But where would I even put that script? That would have to be on another page, which would break the whole idea of REST. Then I would just be GETing another page, which would in turn DELETE the page I originally intended?

Is this why people rarely use REST or is there actually a nice way to do this?

---

Looks like I need to clarify. People are suggesting I include words like "DELETE" and "POST" in the URL. I believe REST dictates that we have a unique URL for each resource but not for each action on that resource. I assume this also means that we only have one and only one URL for each resource. i.e. I want to be able to DELETE or VIEW the contents of a particular post from one URL (by sending either DELETE, PUT, POST, or GET), not different URLs with additional params

回答1:

With a restful server, the same url (say /books/1) can respond to many different verbs. Those verbs, GET, POST, PUT, and DELETE, together with the path, indicate what you want to do to the data on the server. The response tells you the answer to your request.

REST is about accessing data in a predictable and sensible way.

If you come from a strong PHP background, where every url has to map to a particular file, you're right, it doesn't really make sense. The two most visible RESTful development environments, ASP.NET MVC and Rails, each have special servers (or server logic) which read the verbs and do that special routing for you. That's what lets the "normal flow" of the application go through as you'd expect. For PHP, there are frameworks that help with this, such as WSO2's WSF.

How REST works with Web Browsers

Take, for instance, your example. We have posts, and we want to delete one.

1. We start by visiting a url like /posts/4. As we would expect, this shows post 4, its attributes, and some actions you could take on it. The request to render this url would look like GET /posts/4. The response contains HTML that describes the item.

2. The user clicks the "Delete Item 4" link, part of the HTML. This sends a request like DELETE /posts/4 to the server. Notice, this has re-used the /posts/4 url, but the logic must be different.

   Of HTML forms and web browsers, many of them will change a link with method="delete" into a method="post" link by default. You will need to use Javascript (something like this) to change the verb. Ruby on Rails uses a hidden input field (_method) to indicate which method is to be used on a form, as an alternative.

3. On the server side, the "delete an item" logic is executed. It knows to execute this because of the verb in the request (DELETE), which matches the action being performed. That's a key point of REST, that the HTTP verbs become meaningful.

4. After deleting the item, you could respond with a page like "yep, done," or "no, sorry, you can't do that," but for a browser it makes more sense to put you somewhere else. The item being deleted, responding with a redirect to GET /posts makes good sense.

If you look at the server log, it will be very clear what everybody did to the server, but that's not as important as...

How REST works with Arbitrary Data

Another key point of REST is that it works well with multiple data formats. Suppose you were writing a program that wanted to read and interact with the blog programmatically. You might want all the posts given in XML, rather than having to scrape the HTML for information.

GET /posts/4.xml is intuitive: "Server, please give me xml describing post #4." The response will be that xml. A RESTful server makes it obvious how to get the information you want.

When you made the DELETE /posts/4.xml request, you're asking, "Server, please delete item #4." A response like, "Okay, sure," is usually sufficient to express what's happened. The program can then decide what else it wants and make another request.

回答2:

Well one way is to make an AJAX call using the DELETE method.

回答3:

Facebook's REST server is a pseudo one, you can do it like them, asking for the post method: POST, GET, etc. the action and the other values you need for that request.

Why I say facebook is a pseudo REST server? : well, one of the Principles of REST says

• Every resource is uniquely addressable using a universal syntax for use in hypermedia links

in facebook you only have /server.php and there is where you make the request, even for (POST, GET, PUT, DELETE...)

the other way is using mod_rewrite and parse the url the client is requesting

EDIT: just found this, looks interesting. Have fun!

回答4:

I don't think REST is rarely used. You're using it right now, on StackOverflow. As far as your specific example goes, you can send DELETE requests though XMLHttpRequest in browsers that support it. When JS is off, or for non-compliant browsers, you can do something like:

POST http://foo.com/delete?post=5

Not ideal, but still more restful than many sites.

EDIT: Changed to POST

回答5:

Depending on what framework you use, there are models that determine how actions are handled for each resource.

Basically using another parameter, you want to send the resource what action to perform. That parameter may be sent through AJAX/JS for example.

If you want to do it without javascript/ajax (in case it's disabled), then a form POST method would work as well, sending the resource the extra ACTION parameter.

Of course, in both cases, you have to consider security, and make sure that they're not sending the resource an action they shouldn't be. Make sure to do your checking on the backend, and send an appropriate response or error message.

Client side scripting, whether through JS/Ajax or form POST or other methods require the extra security precaution.

Edited after clarification from poster.

回答6:

Don't overthink it. You're not going to be able to do this with straight HTML forms and a browser. They do not support DELETE method. Ajax can do it.

I want to be able to DELETE to VIEW the contents of a particular post from one URL (by sending either DELETE, PUT, POST, or GET), not different URLs with additional params

Delete to view? I'm not sure I understand it, but your delete should be done through the headers, not through the URL. The delete method should not return a view. REST is a service, not all requests are meant for visual consumption.

回答7:

If you really have no choice about using the DELETE verb then I would suggest something like the following:

POST http://mysite.com/Trashcan?resourceUrl=/Customer/75

What url you use really does not matter to REST, however, it is easier to understand the REST way of interacting if your urls avoid verbs completely.

I have seen so many questions from both Rails and ASP.NET MVC users who need to go beyond the standard "actions" and it is so tempting to just add a new action on the controller. The problem with doing this is that you just threw away the uniform interface constraint of REST.

The trashcan metaphor is not the only way of doing deletes restfully but I would argue that it is just as clear to read as putting a "delete" in the url.

Here are some more "noun-based" ways of replacing verbs.

POST http://mysite.com/Printer/75/PrintQueue?url=http://mysite.com/Document/xyz
POST http://mysite.com/CurrentLogins?user=bob
POST http://mysite.com/QueryProcessor?query=FindMyInformation
POST http://mysite.com/SearchEngine?searchTerms=cat,blue,furry
POST http://mysite.com/OrderProcessor?cart=http://mysite.com/user/2323/cart

Sometimes you have to think out of the box a little to come up with a noun based url, and may seem pedantic to try and do this, but for me the benefit comes from the ability to manage my variables. I am going to have a variable number of resources in my interface, no matter what I do, if I can fix the number of verbs that can operate on those resources then I reduce one of my variables.

回答8:

Another way of doing it, assuming a webbased/webapplication-based request, is have 2 submitbuttons. Since PUT and DELETE use the same uri/url. You could add a specific delete form and attach a specific name to this delete-button, so when this is sent via a post, you can use this button-name to turn the action into a DELETE