REST: Updating Multiple Resources With One Request

问题:

A simple REST API:

• GET: items/{id} - Returns a description of the item with the given id
• PUT: items/{id} - Updates or Creates the item with the given id
• DELETE: items/{id} - Deletes the item with the given id

Now the API-extension in question:

• GET: items?filter - Returns all item ids matching the filter
• PUT: items - Updates or creates a set of items as described by the JSON payload
• [[DELETE: items - deletes a list of items described by JSON payload]] <- Not Correct

I am now being interested in the DELETE and PUT operation recycling functionality that can be easily accessed by PUT/DELETE items/{id}.

Question: Is it common to provide an API like this?

Alternative: In the age of Single Connection Multiple Requests issuing multiple requests is cheap and would work more atomic since a change either succeeds or fails but in the age of NOSQL database a change in the list might already have happend even if the request processing dies with internal server or whatever due to whatever reason.

[UPDATE]

After considering White House Web Standards and Wikipedia: REST Examples the following Example API is now purposed:

A simple REST API:

• GET: items/{id} - Returns a description of the item with the given id
• PUT: items/{id} - Updates or Creates the item with the given id
• DELETE: items/{id} - Deletes the item with the given id

Top-resource API:

• GET: items?filter - Returns all item ids matching the filter
• POST: items - Updates or creates a set of items as described by the JSON payload

PUT and DELETE on /items is not supported and forbidden.

Using POST seems to do the trick as being the one to create new items in an enclosing resource while not replacing but appending.

HTTP Semantics POST Reads:

Extending a database through an append operation

Where the PUT methods would require to replace the complete collection in order to return an equivalent representation as quoted by HTTP Semantics PUT:

A successful PUT of a given representation would suggest that a subsequent GET on that same target resource will result in an equivalent representation being returned in a 200 (OK) response.

[UPDATE2]

An alternative that seems even more consistent for the update aspect of multiple objects seems to be the PATCH method. The difference between PUT and PATCH is described in the Draft RFC 5789 as being:

The difference between the PUT and PATCH requests is reflected in the way the server processes the enclosed entity to modify the resource identified by the Request-URI. In a PUT request, the enclosed entity is considered to be a modified version of the resource stored on the origin server, and the client is requesting that the stored version be replaced. With PATCH, however, the enclosed entity contains a set of instructions describing how a resource currently residing on the origin server should be modified to produce a new version. The PATCH method affects the resource identified by the Request-URI, and it also MAY have side effects on other resources; i.e., new resources may be created, or existing ones modified, by the application of a PATCH.

So compared to POST, PATCH may be also a better idea since PATCH allows an UPDATE where as POST only allows appending something meaning adding without the chance of modification.

So POST seems to be wrong here and we need to change our proposed API to:

A simple REST API:

• GET: items/{id} - Returns a description of the item with the given id
• PUT: items/{id} - Updates or Creates the item with the given id
• DELETE: items/{id} - Deletes the item with the given id

Top-resource API:

• GET: items?filter - Returns all item ids matching the filter
• POST: items - Creates one or more items as described by the JSON payload
• PATCH: items - Creates or Updates one or more items as described by the JSON payload

回答1:

You could PATCH the collection, e.g.

PATCH /items
[ { id: 1, name: 'foo' }, { id: 2, name: 'bar' } ]

Technically PATCH would identify the record in the URL (ie PATCH /items/1 and not in the request body, but this seems like a good pragmatic solution.

To support deleting, creating, and updating in a single call, that's not really supported by standard REST conventions. One possibility is a special "batch" service that lets you assemble calls together:

POST /batch
[
  { method: 'POST', path: '/items', body: { title: 'foo' } },
  { method: 'DELETE', path: '/items/bar' }
]

which returns a response with status codes for each embedded requests:

[ 200, 403 ]

Not really standard, but I've done it and it works.

回答2:

As far as I understand the REST concept it covers an update of multiple resources with one request. Actually the trick here is to assume a container around those multiple resources and take it as one single resource. E.g. you could just assume that list of IDs identifies a resource that contains several other resources.

In those examples in Wikipedia they also talk about resources in Plural.

回答3:

Updating Multiple Resources With One Request - Is it standard or to be avoided?

Well, sometimes you simply need to perform atomic batch operations or other resource-related operations that just do not fit the typical scheme of a simple REST API, but if you need it, you cannot avoid it.

Is it standard?

There is no universally accepted REST API standard so this question is hard to answer. But by looking at some commonly quoted api design guidelines, such as jsonapi.org, restfulapi.net, microsoft api design guide or IBM's REST API Conventions, which all do not mention batch operations, you can infer that such operations are not commonly understood as being a standard feature of REST APIs.

That said, an exception is the google api design guide which mentions the creation of "custom" methods that can be associated via a resource by using a colon, e.g. https://service.name/v1/some/resource/name:customVerb, it also explicitly mentions batch operations as use case:

A custom method can be associated with a resource, a collection, or a service. It may take an arbitrary request and return an arbitrary response, and also supports streaming request and response. [...] Custom methods should use HTTP POST verb since it has the most flexible semantics [...] For performance critical methods, it may be useful to provide custom batch methods to reduce per-request overhead.

So in the example case you provided you do the following according to google's api guide:

POST /api/items:batchUpdate

Also, some public APIs decided to offer a central /batch endpoint, e.g. google's gmail API.

Moreover, as mentioned at restfulapi.net, there is also the concept of a resource "store", in which you store and retrieve whole lists of items at once via PUT – however, this concept does not count for server-managed resource collections:

A store is a client-managed resource repository. A store resource lets an API client put resources in, get them back out, and decide when to delete them. A store never generates new URIs. Instead, each stored resource has a URI that was chosen by a client when it was initially put into the store.

---

Having answered your original questions, here is another approach to your problem that has not been mentioned yet. Please note that this approach is a bit unconventional and does not look as pretty as the typical REST API endpoint naming scheme. I am personally not following this approach but I still felt it should be given a thought :)

The idea is that you could make a distinction between CRUD operations on a resource and other resource-related operations (e.g. batch operations) via your endpoint path naming scheme.

For example consider a RESTful API that allows you to perform CRUD operations on a "company"-resource and you also want to perform some "company"-related operations that do not fit in the resource-oriented CRUD-scheme typically associated with restful api's – such as the batch operations you mentioned.

Now instead of exposing your resources directly below /api/companies (e.g. /api/companies/22) you could distinguish between:

• /api/companies/items – i.e. a collection of company resources
• /api/companies/ops – i.e. operations related to company resources

For items the usual RESTful api http-methods and resource-url naming-schemes apply (e.g. as discussed here or here)

POST    /api/companies/items
GET     /api/companies/items
GET     /api/companies/items/{id}
DELETE  /api/companies/items/{id}
PUT     /api/companies/items/{id}

Now for company-related operations you could use the /api/companies/ops/ route-prefix and call operations via POST.

POST    /api/companies/ops/batch-update
POST    /api/companies/ops/batch-delete
POST    /api/companies/ops/garbage-collect-old-companies
POST    /api/companies/ops/increase-some-timestamps-just-for-fun
POST    /api/companies/ops/perform-some-other-action-on-companies-collection

Since POST requests do not have to result in the creation of a resource, POST is the right method to use here:

The action performed by the POST method might not result in a resource that can be identified by a URI. https://tools.ietf.org/html/rfc2616#section-9.5