REST: Best practice for partial update of subset of collection - rest

Question

I am trying to understand a little bit more about the REST ways :). Let's say I have a collection of ProductTypes that one can retrive via url GET /productTypes and let's say that we can but don't have to apply any filter. So this fetches 500 records.
Now if I want to do full update of the resource I could use PUT or POST at /productTypes/123. So far so good.
If I am creating a new resource and I know the id ahead of time, I would use PUT at /productTypes/123 and return 201 otherwise for update PUT with 200.
If I do partial update of the resource I would do PUT or POST at /productTypes/123/displayOrder and return 303 indicating that some other resource has been modified.
But what if I do 1 POST sending in basically a list of Key-Value pairs of product Id and display order, and I modify 5 out of 500 records. How do I indicate now that these 5 records have changed?
What happens with GET at /productTypes now after this partial update. I read somewhere that instead of returning multiple records with this get, I should return the list links to the resources, and then fetch them one by one, as that would allow for insane caching. But still how do I indicate that 5 records have changed? Do I need to do 5 separate posts with 303, or is there different mechanism. Hope this makes sense.

Answer 1

I don't see anything in the spec that specifically bars you from using multiple Content-Location headers. I tested it out and Chrome's totally OK with it. It won't automatically redirect for you, but you don't want that anyway with multiple resources involved.
HTTP/1.1 303 See Other
Content-Location: /productTypes/123/displayOrder
Content-Location: /productTypes/456/displayOrder
Content-Location: /productTypes/789/displayOrder
Content-Location: /productTypes/012/displayOrder
Content-Location: /productTypes/345/displayOrder

Answer 2

I'd do this:
PATCH /productTypes HTTP/1.1
Content-Type: application/json
{"item":[
{"id":"1","displayOrder":"4"},
{"id":"2","displayOrder":"2"},
{"id":"3","displayOrder":"1"},
{"id":"4","displayOrder":"3"},
{"id":"5","displayOrder":"5"}
]}
HTTP/1.1 200 OK
Content-Type: application/hal+json
{
"_links": { "self": {"href": "/productTypes" } }
"_embedded": {
"item": [{
"_links": { "self": { "href": "/productTypes/1" } },
"displayOrder": "4"
},
/* 4 more entries */
]
}
}