I have an object:
Account
{
Id,
Name,
CurrentBalance
}
Id is an immutable key, Name is a mutable string, and CurrentBalance is calculated from all of the transactions associated with the account.
I am stuck on the fact that GET \Accounts\{Id} will not be idempotent because changes to a transaction will cause a change in CurrentBalance. Should I remove this field from the object and make a request like
POST \Accounts\{Id}\CurrentBalance
But now I have to make multiple calls to the server to get the CurrentBalance of all objects:
GET \Accounts
POST \Accounts\{Id1}\CurrentBalance
POST \Accounts\{Id2}\CurrentBalance
POST \Accounts\{Id3}\CurrentBalance
....
I guess I am just looking to see if there is already a standard way to handle this that I am missing?
UPDATE
Part 2 if the original object is ok via GET. My only way to update the Account.Name is via a PATCH as I cannot allow an update to CurrentBalance, correct?
NOTE
I realize I could put this on the client to have to get all transactions and calculate it, but I would prefer to do this on the server for multiple reasons
Idempotency does not mean that you must always get the same response back.
Consider the resource /TodaysWeather. It would be pretty useless if it always returned the same value.
Idempotency simply states that if a client makes the same request multiple times instead of just once, the impact on the system (from the client's perspective) will be the same.
I just re-read the HTTP specs and realized that if I want to be truly RESTful I have to make multiple calls because GET has to be safe.
In particular, the convention has been established that the GET and
HEAD methods SHOULD NOT have the significance of taking an action
other than retrieval.
I am not deleting this question because I think it could help others in the future, but if the majority disagree I will delete it
If it's important that you're able to PUT some data, then immediately retrieve the same data via GET, then you could simply treat it as a different resource entirely, e.g.:
# Change an account name
PUT \Accounts\{id}
# Get accounts/names/balances
GET \AccountDetails
# Get balance of an account
GET \AccountDetails\{id}\CurrentBalance
However, there's really no good reason to go through the trouble of doing that. Your PUT is idempotent as long as making the same request multiple times doesn't change the state of the system. Not changing the system's state if some spurious value is submitted is the correct behavior. In fact, if someone does try a PUT including CurrentBalance, you might want to return a 400 (Bad Request) status explaining that CurrentBalance can't be updated.
Related
For a while I was (wrongly) thinking that a RESTful API just exposed CRUD operation to persisted entities for a web application. When you code something up in "the real world" you soon find out that this is not enough. For example, a bank account transfer doesn't have to be a persisted entity. It could be a transient resource where you POST to /transfers/ and in the payload you specify the details:
{"accountToCredit":1234, "accountToDebit":5678, "amount":10}
Using POST here makes sense because it changes the state on the server ($10 moves from one account to another every time this POST occurs).
What should happen in the case where it doesn't affect the server? The simple first answer would be to use GET. For example, you want to get a list of savings and checking accounts that have less than $100. You would then call something like GET to /accounts/searchResults?minBalance=0&maxBalance=100. What happens though if your search parameter need to use complex objects that wouldn't fit in the maximum length of a GET request.
My first thought was to use POST, but after thinking about it some more it should probably be a PUT since it isn't changing the state of the server, but from my (limited) understanding I always though of PUT as updating a resource and POST as creating a resource (like creating this search results). So which should be used in this case?
I found the following links which provide some information but it wasn't clear to me what should be used in the different cases:
Transient REST Representations
How to design RESTful search/filtering?
RESTful URL design for search
I would agree with your approach, it seems reasonable to me to use GET when searching for resources, and as said in one of your provided links, the whole point of query strings is for doing things like search. I also agree that PUT fits better when you want to update some resource in an idempotent way (no matter how many times you hit the request, the result will be the same).
So generally, I would do it as you propose. Now, if you are limited by the maximum length of GET request, then you could use POST or PUT, passing your parameters in a JSON, in a URI like:
PUT /api/search
You could see this as a "search resource" where you send new parameters. I know it seems like a workaround and you may be worried that REST is about avoiding verbs in the URIs. Well, there are few cases that it's still acceptable and RESTful to use verbs, e.g. in cases where calculation or conversion is involved to generate the result (for more about this, check this reference).
PS. I think this workaround is still RESTful, but even if it wasn't, REST isn't an obsession and an ultimate goal. Being pragmatic and keeping a clean API design might be a better approach, even if in few cases you are not RESTful.
As stated in http://www.boutell.com/newfaq/misc/urllength.html, HTTP query string have limited length. It can be limited by the client (Firefox, IE, ...), the server (Apache, IIS, ...) or the network equipment (applicative firewall, ...).
Today I face this problem with a search form. We developed a search form with a lot of fields, and this form is sent to the server as a GET request, so I can bookmark the resulting page.
We have so many fields that our query string is 1100 bytes long, and we have a firewall that drops HTTP GET requests with more than 1024 bytes. Our system administrator recommends us to use POST instead so there will be no limitation.
Sure, POST will work, but I really feel a search as a GET and not a POST. So I think I will review our field names to ensure the query string is not too long, and if I can't I will be pragmatic and use POST.
But is there a flaw in the design of RESTful services? If we have limited length in GET request, how can I do to send large objects to a RESTful webservice? For example, if I have a program that makes calculations based on a file, and I want to provide a RESTful webservice like this: http://compute.com?content=<base64 file>. This won't work because the query string has not unlimited length.
I'm a little puzzled...
HTTP specification actually advises to use POST when sending data to a resource for computation.
Your search looks like a computation, not a resource itself. What you could do if you still want your search results to be a resource is create a token to identify that specific search result and redirect the user agent to that resource.
You could then delete search results tokens after some amount of time.
Example
POST /search
query=something&category=c1&category=c2&...
201 Created
Location: /search/01543164876
then
GET /search/01543164876
200 Ok
... your results here...
This way, browsers and proxies can still cache search results but you are submitting your query parameters using POST.
EDIT
For clarification, 01543164876 here represents a unique ID for the resource representing your search. Those 2 requests basically mean: create a new search object with these criteria, then retrieve the results associated with the created search object.
This ID can be a unique ID generated for each new request. This would mean that your server will leak "search" objects and you will have to clean them regularly with a caching strategy.
Or it can be a hash of all the search criteria actually representing the search asked by the user. This allows you to reuse IDs since recreating a search will return an existing ID that may (or may not) be already cached.
Based on your description, IMHO you should use a POST. POST is for putting data on the server and, in some cases, obtain an answer. In your case, you do a search (send a query to the server) and get the result of that search (retrieve the query result).
The definition of GET says that it must be used to retrieve an already existing resource. By definition, POST is to create a new resource. This is exactly what you are doing: creating a resource on the server and retrieving it! Even if you don't store the search result, you created an object on the server and retrieved it. As PeterMmm previsouly said, you could do this with a POST (create and store the query result) and then use a GET to retrive the query, but it's more pratical do only a POST and retrieve the result.
Hope this helps! :)
REST is a manner to do things, not a protocol. Even if you dislike to POST when it is really a GET, it will work.
If you will/must stay with the "standard" definition of GET, POST, etc. than maybe consider to POST a query, that query will be stored on the server with a query id and request the query later with GET by id.
Regarding your example:http://compute.com?content={base64file}, I would use POST because you are uploading "something" to be computed. For me this "something" feels more like a resource as a simple parameter.
In contrast to this in usual search I would start to stick with GET and parameters. You make it so much easier for api-clients to test and play around with your api. Make the read-only access (which in most cases is the majority of traffic) as simple as possible!
But the dilemma of large query strings is a valid limitation of GET. Here I would go pragmatic, as long as you don't hit this limit go with GET and url-params. This will work in 98% of search-cases. Only act if you hit this limit and then also introduce POST with payload (with mime-type Content-Type: application/x-www-form-urlencoded).
Have you got more real-world examples?
The confusion around GET is a browser limitation. If you are creating a RESTful interface for an A2A or P2P application then there is no limitation to the length of your GET.
Now, if you happen to want to use a browser to view your RESTful interface (aka during development/debugging) then you will run into this limit, but there are tools out there to get around this.
This is an easy one. Use POST. HTTP doesn't impose a limit on the URL length for GET but servers do. Be pragmatic and work around that with a POST.
You could also use a GET body (that is allowed) but that's a double-whammy in that it is not correct usage and probably going to have server problems.
I think if u develop the biz system, encounter this issue, u must think whether the api design reasonable, if u GET api param design a biz_ids, and it too long.
u should think about with UI or Usecase, whether use other_biz_id to find biz_ids and build target response instead of biz_ids directly or not.
if u old api be depended on, u can add a new api for this usecase, if u module design well u add this api may fast.
I think should use protocols in a standard way as developer.
hope help u.
This question already has answers here:
When should I use GET or POST method? What's the difference between them?
(15 answers)
Closed 9 years ago.
I've only recently been getting involved with PHP/AJAX/jQuery and it seems to me that an important part of these technologies is that of POST and GET.
First, what is the difference between POST and GET? Through experimenting, I know that GET appends the returning variables and their values to the URL string
website.example/directory/index.php?name=YourName&bday=YourBday
but POST doesn't.
So, is this the only difference or are there specific rules or conventions for using one or the other?
Second, I've also seen POST and GET outside of PHP: also in AJAX and jQuery. How do POST and GET differ between these 3? Are they the same idea, same functionality, just utilized differently?
GET and POST are two different types of HTTP requests.
According to Wikipedia:
GET requests a representation of the specified resource. Note that GET should not be used for operations that cause side-effects, such as using it for taking actions in web applications. One reason for this is that GET may be used arbitrarily by robots or crawlers, which should not need to consider the side effects that a request should cause.
and
POST submits data to be processed (e.g., from an HTML form) to the identified resource. The data is included in the body of the request. This may result in the creation of a new resource or the updates of existing resources or both.
So essentially GET is used to retrieve remote data, and POST is used to insert/update remote data.
HTTP/1.1 specification (RFC 2616) section 9 Method Definitions contains more information on GET and POST as well as the other HTTP methods, if you are interested.
In addition to explaining the intended uses of each method, the spec also provides at least one practical reason for why GET should only be used to retrieve data:
Authors of services which use the HTTP protocol SHOULD NOT use GET based forms for the submission of sensitive data, because this will cause this data to be encoded in the Request-URI. Many existing servers, proxies, and user agents will log the request URI in some place where it might be visible to third parties. Servers can use POST-based form submission instead
Finally, an important consideration when using GET for AJAX requests is that some browsers - IE in particular - will cache the results of a GET request. So if you, for example, poll using the same GET request you will always get back the same results, even if the data you are querying is being updated server-side. One way to alleviate this problem is to make the URL unique for each request by appending a timestamp.
A POST, unlike a GET, typically has relevant information in the body of the request. (A GET should not have a body, so aside from cookies, the only place to pass info is in the URL.) Besides keeping the URL relatively cleaner, POST also lets you send much more information (as URLs are limited in length, for all practical purposes), and lets you send just about any type of data (file upload forms, for example, can't use GET -- they have to use POST plus a special content type/encoding).
Aside from that, a POST connotes that the request will change something, and shouldn't be redone willy-nilly. That's why you sometimes see your browser asking you if you want to resubmit form data when you hit the "back" button.
GET, on the other hand, should be idempotent -- meaning you could do it a million times and the server will do the same thing (and show basically the same result) each and every time.
Whilst not a description of the differences, below are a couple of things to think about when choosing the correct method.
GET requests can get cached by the browser which can be a problem (or benefit) when using ajax.
GET requests expose parameters to users (POST does as well but they are less visible).
POST can pass much more information to the server and can be of almost any length.
POST and GET are two HTTP request methods. GET is usually intended to retrieve some data, and is expected to be idempotent (repeating the query does not have any side-effects) and can only send limited amounts of parameter data to the server. GET requests are often cached by default by some browsers if you are not careful.
POST is intended for changing the server state. It carries more data, and repeating the query is allowed (and often expected) to have side-effects such as creating two messages instead of one.
If you are working RESTfully, GET should be used for requests where you are only getting data, and POST should be used for requests where you are making something happen.
Some examples:
GET the page showing a particular SO question
POST a comment
Send a POST request by clicking the "Add to cart" button.
With POST you can also do multipart mime encoding which means you can attach files as well. Also if you are using post variables across navigation of pages, the user will get a warning asking if they want to resubmit the post parameter. Typically they look the same in an HTTP request, but you should just stick to POST if you need to "POST" something TO a server and "GET" if you need to GET something FROM a server as that's the way they were intended.
The only "big" difference between POST & GET (when using them with AJAX) is since GET is URL provided, they are limited in ther length (since URL arent infinite in length).
Thinking about REST, it's relatively easy to map HTTP methods to CRUD actions: POST for create, GET for read, etc. But what about "fire and forget" actions? What HTTP method would best represent a fire and forget action such as triggering a batch job (in which no response is sent back to the caller)?
POST would spring to mind, but I think GET is also an appropriate method because 99% of the time you only supply a bunch of parameters to these types of actions. What do you think?
POST would spring to mind, but I think GET is a more appropriate method because 99% of the time you only supply a bunch of parameters to these types of actions. What do you think?
External State
I think that the number of parameters you use has nothing to do with the verb you use. The key issue is are you changing externally visible state?
BatchJob Resources
In your example, if the batch job does not affect the externally visible state of any object then you could implement it as a batch job. However you could model your batch job as a resource with an associated resource container.
You could use a Post to create a new BatchJob resource and allow the user to do a GET to see the progress of the job so far. You could do a GET on the resource container to list all of the running batch jobs, possibly calling DELETE to kill one.
You should use POST if your request modifies data, and GET if it only reads it.
Since your request is "fire and forget", I guess that it's modifying data, so use POST.
I think in the general case we might well supply various payload parameters, and these plausibly might exceed what's possible with GET, so POST is quite reasonable - the action of starting a job doesn't to me fit well with GET sematics.
One thought, might not the action actually return a response:
a). No, sir, that's an impossible request we can't start your job.
b). Understood, your job reference is 93.
If you're concerned at that level, perhaps HEAD is the HTTP method you want; it's identical to GET, with the stipulation that the response body is empty. That sounds to me spot-on to what you're asking for?
I'm bringing this question back from the dead to offer a different point of view.
Now that CORS is prevalent, the choice between using GET or POST becomes a matter of if you want anyone who knows your API URI to be able to trigger the batch job (GET), or if you want to restrict the origin of the request to prevent any Joe with a computer from triggering the job (POST).
I have a resource that has a counter. For the sake of example, let's call the resource profile, and the counter is the number of views for that profile.
Per the REST wiki, PUT requests should be used for resource creation or modification, and should be idempotent. That combination is fine if I'm updating, say, the profile's name, because I can issue a PUT request which sets the name to something 1000 times and the result does not change.
For these standard PUT requests, I have browsers do something like:
PUT /profiles/123?property=value&property2=value2
For incrementing a counter, one calls the url like so:
PUT /profiles/123/?counter=views
Each call will result in the counter being incremented. Technically it's an update operation but it violates idempotency.
I'm looking for guidance/best practice. Are you just doing this as a POST?
I think the right answer is to use PATCH. I didn't see anyone else recommending it should be used to atomically increment a counter, but I believe RFC 2068 says it all very well:
The PATCH method is similar to PUT except that the entity contains a
list of differences between the original version of the resource
identified by the Request-URI and the desired content of the resource
after the PATCH action has been applied. The list of differences is
in a format defined by the media type of the entity (e.g.,
"application/diff") and MUST include sufficient information to allow
the server to recreate the changes necessary to convert the original
version of the resource to the desired version.
So, to update profile 123's view count, I would:
PATCH /profiles/123 HTTP/1.1
Host: www.example.com
Content-Type: application/x-counters
views + 1
Where the x-counters media type (which I just made up) is made of multiple lines of field operator scalar tuples. views = 500 or views - 1 or views + 3 are all valid syntactically (but may be forbidden semantically).
I can understand some frowning-upon making up yet another media type, but I humbly suggest it's more correct than the POST / PUT alternative. Making up a resource for a field, complete with its own URI and especially its own details (which I don't really keep, all I have is an integer) sounds wrong and cumbersome to me. What if I have 23 different counters to maintain?
An alternative might be to add another resource to the system to track the viewings of a profile. You might call it "Viewing".
To see all Viewings of a profile:
GET /profiles/123/viewings
To add a viewing to a profile:
POST /profiles/123/viewings #here, you'd submit the details using a custom media type in the request body.
To update an existing Viewing:
PUT /viewings/815 # submit revised attributes of the Viewing in the request body using the custom media type you created.
To drill down into the details of a viewing:
GET /viewings/815
To delete a Viewing:
DELETE /viewings/815
Also, because you're asking for best-practice, be sure your RESTful system is hypertext-driven.
For the most part, there's nothing wrong with using query parameters in URIs - just don't give your clients the idea that they can manipulate them.
Instead, create a media type that embodies the concepts the parameters are trying to model. Give this media type a concise, unambiguous, and descriptive name. Then document this media type. The real problem of exposing query parameters in REST is that the practice often leads out-of-band communication, and therefore increased coupling between client and server.
Then give your system a uniform interface. For example, adding a new resource is always a POST. Updating a resource is always a PUT. Deleting is DELETE, and getiing is GET.
The hardest part about REST is understanding how media types figure into system design (it's also the part that Fielding left out of his dissertation because he ran out of time). If you want a specific example of a hypertext-driven system that uses and doucuments media types, see the Sun Cloud API.
After evaluating the previous answers I decided PATCH was inappropriate and, for my purposes, fiddling around with Content-Type for a trivial task was a violation of the KISS principle. I only needed to increment n+1 so I just did this:
PUT /profiles/123$views
++
Where ++ is the message body and is interpreted by the controller as an instruction to increment the resource by one.
I chose $ to deliminate the field/property of the resource as it is a legal sub-delimiter and, for my purposes, seemed more intuitive than / which, in my opinion, has the vibe of traversability.
I think both approaches of Yanic and Rich are interresting. A PATCH does not need to be safe or indempotent but can be in order to be more robust against concurrency. Rich's solution is certainly easier to use in a "standard" REST API.
See RFC5789:
PATCH is neither safe nor idempotent as defined by [RFC2616], Section
9.1.
A PATCH request can be issued in such a way as to be idempotent,
which also helps prevent bad outcomes from collisions between two
PATCH requests on the same resource in a similar time frame.
Collisions from multiple PATCH requests may be more dangerous than
PUT collisions because some patch formats need to operate from a
known base-point or else they will corrupt the resource.