[rest] Best practice for partial updates in a RESTful service

I am writing a RESTful service for a customer management system and I am trying to find the best practice for updating records partially. For example, I want the caller to be able to read the full record with a GET request. But for updating it only certain operations on the record are allowed, like change the status from ENABLED to DISABLED. (I have more complex scenarios than this)

I don't want the caller to submit the entire record with just the updated field for security reasons (it also feels like overkill).

Is there a recommended way of constructing the URIs? When reading the REST books RPC style calls seem to be frowned upon.

If the following call returns the full customer record for the customer with the id 123

GET /customer/123
<customer>
    {lots of attributes}
    <status>ENABLED</status>
    {even more attributes}
</customer>

how should I update the status?

POST /customer/123/status
<status>DISABLED</status>

POST /customer/123/changeStatus
DISABLED

...

Update: To augment the question. How does one incorporate 'business logic calls' into a REST api? Is there an agreed way of doing this? Not all of the methods are CRUD by nature. Some are more complex, like 'sendEmailToCustomer(123)', 'mergeCustomers(123, 456)', 'countCustomers()'

POST /customer/123?cmd=sendEmail

POST /cmd/sendEmail?customerId=123

GET /customer/count 

You basically have two options:

1. Use PATCH (but note that you have to define your own media type that specifies what will happen exactly)

2. Use POST to a sub resource and return 303 See Other with the Location header pointing to the main resource. The intention of the 303 is to tell the client: "I have performed your POST and the effect was that some other resource was updated. See Location header for which resource that was." POST/303 is intended for iterative additions to a resources to build up the state of some main resource and it is a perfect fit for partial updates.

It doesn't matter. In terms of REST, you can't do a GET, because it's not cacheable, but it doesn't matter if you use POST or PATCH or PUT or whatever, and it doesn't matter what the URL looks like. If you're doing REST, what matters is that when you get a representation of your resource from the server, that representation is able give the client state transition options.

If your GET response had state transitions, the client just needs to know how to read them, and the server can change them if needed. Here an update is done using POST, but if it was changed to PATCH, or if the URL changes, the client still knows how to make an update:

{
  "customer" :
  {
  },
  "operations":
  [
    "update" : 
    {
      "method": "POST",
      "href": "https://server/customer/123/"
    }]
}

You could go as far as to list required/optional parameters for the client to give back to you. It depends on the application.

As far as business operations, that might be a different resource linked to from the customer resource. If you want to send an email to the customer, maybe that service is it's own resource that you can POST to, so you might include the following operation in the customer resource:

"email":
{
  "method": "POST",
  "href": "http://server/emailservice/send?customer=1234"
}

Some good videos, and example of the presenter's REST architecture are these. Stormpath only uses GET/POST/DELETE, which is fine since REST has nothing to do with what operations you use or how URLs should look (except GETs should be cacheable):

https://www.youtube.com/watch?v=pspy1H6A3FM,
https://www.youtube.com/watch?v=5WXYw4J4QOU,
http://docs.stormpath.com/rest/quickstart/

Regarding your Update.

The concept of CRUD I believe has caused some confusion regarding API design. CRUD is a general low level concept for basic operations to perform on data, and HTTP verbs are just request methods (created 21 years ago) that may or may not map to a CRUD operation. In fact, try to find the presence of the CRUD acronym in the HTTP 1.0/1.1 specification.

A very well explained guide that applies a pragmatic convention can be found in the Google cloud platform API documentation. It describes the concepts behind the creation of a resource based API, one that emphasizes a big amount of resources over operations, and includes the use cases that you are describing. Although is a just a convention design for their product, I think it makes a lot of sense.

The base concept here (and one that produces a lot of confusion) is the mapping between "methods" and HTTP verbs. One thing is to define what "operations" (methods) your API will do over which types of resources (for example, get a list of customers, or send an email), and another are the HTTP verbs. There must be a definition of both, the methods and the verbs that you plan to use and a mapping between them.

It also says that, when an operation does not map exactly with a standard method (List, Get, Create, Update, Delete in this case), one may use "Custom methods", like BatchGet, which retrieves several objects based on several object id input, or SendEmail.

Things to add to your augmented question. I think you can often perfectly design more complicated business actions. But you have to give away the method/procedure style of thinking and think more in resources and verbs.

mail sendings

POST /customers/123/mails

payload:
{from: [email protected], subject: "foo", to: [email protected]}

The implementation of this resource + POST would then send out the mail. if necessary you could then offer something like /customer/123/outbox and then offer resource links to /customer/mails/{mailId}.

customer count

You could handle it like a search resource (including search metadata with paging and num-found info, which gives you the count of customers).

GET /customers

response payload:
{numFound: 1234, paging: {self:..., next:..., previous:...} customer: { ...} ....}

Check out http://www.odata.org/

It defines the MERGE method, so in your case it would be something like this:

MERGE /customer/123

<customer>
   <status>DISABLED</status>
</customer>

Only the status property is updated and the other values are preserved.

For modifying the status I think a RESTful approach is to use a logical sub-resource which describes the status of the resources. This IMO is pretty useful and clean when you have a reduced set of statuses. It makes your API more expressive without forcing the existing operations for your customer resource.

Example:

POST /customer/active  <-- Providing entity in the body a new customer
{
  ...  // attributes here except status
}

The POST service should return the newly created customer with the id:

{
    id:123,
    ...  // the other fields here
}

The GET for the created resource would use the resource location:

GET /customer/123/active

A GET /customer/123/inactive should return 404

For the PUT operation, without providing a Json entity it will just update the status

PUT /customer/123/inactive  <-- Deactivating an existing customer

Providing an entity will allow you to update the contents of the customer and update the status at the same time.

PUT /customer/123/inactive
{
    ...  // entity fields here except id and status
}

You are creating a conceptual sub-resource for your customer resource. It is also consistent with Roy Fielding's definition of a resource: "...A resource is a conceptual mapping to a set of entities, not the entity that corresponds to the mapping at any particular point in time..." In this case the conceptual mapping is active-customer to customer with status=ACTIVE.

Read operation:

GET /customer/123/active 
GET /customer/123/inactive

If you make those calls one right after the other one of them must return status 404, the successful output may not include the status as it is implicit. Of course you can still use GET /customer/123?status=ACTIVE|INACTIVE to query the customer resource directly.

The DELETE operation is interesting as the semantics can be confusing. But you have the option of not publishing that operation for this conceptual resource, or use it in accordance with your business logic.

DELETE /customer/123/active

That one can take your customer to a DELETED/DISABLED status or to the opposite status (ACTIVE/INACTIVE).

You should use PATCH for partial updates - either using json-patch documents (see http://tools.ietf.org/html/draft-ietf-appsawg-json-patch-08 or http://www.mnot.net/blog/2012/09/05/patch) or the XML patch framework (see http://tools.ietf.org/html/rfc5261). In my opinion though, json-patch is the best fit for your kind of business data.

PATCH with JSON/XML patch documents has very strait forward semantics for partial updates. If you start using POST, with modified copies of the original document, for partial updates you soon run into problems where you want missing values (or, rather, null values) to represent either "ignore this property" or "set this property to the empty value" - and that leads down a rabbit hole of hacked solutions that in the end will result in your own kind of patch format.

You can find a more in-depth answer here: http://soabits.blogspot.dk/2013/01/http-put-patch-or-post-partial-updates.html.

RFC 7396: JSON Merge Patch (published four years after the question was posted) describes the best practices for a PATCH in terms of the format and processing rules.

In a nutshell, you submit an HTTP PATCH to a target resource with the application/merge-patch+json MIME media type and a body representing only the parts that you want to be changed/added/removed and then follow the below processing rules.

Rules:

• If the provided merge patch contains members that do not appear within the target, those members are added.

• If the target does contain the member, the value is replaced.

• Null values in the merge patch are given special meaning to indicate the removal of existing values in the target.

Example test cases that illustrate the rules above (as seen in the appendix of that RFC):

 ORIGINAL         PATCH           RESULT
--------------------------------------------
{"a":"b"}       {"a":"c"}       {"a":"c"}

{"a":"b"}       {"b":"c"}       {"a":"b",
                                 "b":"c"}
{"a":"b"}       {"a":null}      {}

{"a":"b",       {"a":null}      {"b":"c"}
"b":"c"}

{"a":["b"]}     {"a":"c"}       {"a":"c"}

{"a":"c"}       {"a":["b"]}     {"a":["b"]}

{"a": {         {"a": {         {"a": {
  "b": "c"}       "b": "d",       "b": "d"
}                 "c": null}      }
                }               }

{"a": [         {"a": [1]}      {"a": [1]}
  {"b":"c"}
 ]
}

["a","b"]       ["c","d"]       ["c","d"]

{"a":"b"}       ["c"]           ["c"]

{"a":"foo"}     null            null

{"a":"foo"}     "bar"           "bar"

{"e":null}      {"a":1}         {"e":null,
                                 "a":1}

[1,2]           {"a":"b",       {"a":"b"}
                 "c":null}

{}              {"a":            {"a":
                 {"bb":           {"bb":
                  {"ccc":          {}}}
                   null}}}

You should use POST for partial updates.

To update fields for customer 123, make a POST to /customer/123.

If you want to update just the status, you could also PUT to /customer/123/status.

Generally, GET requests should not have any side effects, and PUT is for writing/replacing the entire resource.

This follows directly from HTTP, as seen here: http://en.wikipedia.org/wiki/HTTP_PUT#Request_methods

Use PUT for updating incomplete/partial resource.

You can accept jObject as parameter and parse its value to update the resource.

Below is the function which you can use as a reference :

public IHttpActionResult Put(int id, JObject partialObject)
{
    Dictionary<string, string> dictionaryObject = new Dictionary<string, string>();

    foreach (JProperty property in json.Properties())
    {
        dictionaryObject.Add(property.Name.ToString(), property.Value.ToString());
    }

    int id = Convert.ToInt32(dictionaryObject["id"]);
    DateTime startTime = Convert.ToDateTime(orderInsert["AppointmentDateTime"]);            
    Boolean isGroup = Convert.ToBoolean(dictionaryObject["IsGroup"]);

    //Call function to update resource
    update(id, startTime, isGroup);

    return Ok(appointmentModelList);
}

I am running into a similar problem. PUT on a sub-resource seems to work when you want to update only a single field. However, sometimes you want to update a bunch of things: Think of a web form representing the resource with option to change some entries. The user's submission of form should not result in a multiple PUTs.

Here are two solution that I can think of:

1. do a PUT with the entire resource. On the server-side, define the semantics that a PUT with the entire resource ignores all the values that haven't changed.

2. do a PUT with a partial resource. On the server-side, define the semantics of this to be a merge.

2 is just a bandwidth-optimization of 1. Sometimes 1 is the only option if the resource defines some fields are required fields (think proto buffers).

The problem with both these approaches is how to clear a field. You will have to define a special null value (especially for proto buffers since null values are not defined for proto buffers) that will cause clearing of the field.

Comments?