Pagination in a REST web application

Question

This is a more generic reformulation of this question (with the elimination of the Rails specific parts)

I am not sure how to implement pagination on a resource in a RESTful web application. Assuming that I have a resource called products, which of the following do you think is the best approach, and why:

1. Using only query strings

eg. http://application/products?page=2&sort_by=date&sort_how=asc
The problem here is that I can't use full page caching and also the URL is not very clean and easy to remember.

2. Using pages as resources and query strings for sorting

eg. http://application/products/page/2?sort_by=date&sort_how=asc
In this case, the problem that is see is that http://application/products/pages/1 is not a unique resource since using sort_by=price can yield a totally different result and I still can't use page caching.

3. Using pages as resources and an URL segment for sorting

eg. http://application/products/by-date/page/2
I personally see no problem in using this method, but someone warned me that this is not a good way to go (he didn't give a reason, so if you know why it's not recommended, please let me know)

Any suggestions, opinions, critiques are more than welcome. Thanks.

Answer 1

I have always used the style of option 1. Caching has not been a concern since the data changes frequently anyway in my case. If you allow the size of the page to be configurable then again the data can't be cached.

I don't find the url hard to remember or unclean. To me this is a fine use of query parameters. The resource is clearly a list of products and the query params are just telling how you want the list displayed - sorted and which page.

Answer 2

HTTP has great Range header which is suitable for pagination too. You may send

Range: pages=1

to have only first page. That may force you to rethink what is a page. Maybe client wants a different range of items. Range header also works to declare an order:

Range: products-by-date=2009_03_27-

to get all products newer than that date or

Range: products-by-date=0-2009_11_30

to get all products older than that date. '0' is probably not best solution, but RFC seems to want something for range start. There may be HTTP parsers deployed which wouldn't parse units=-range_end.

If headers is not an (acceptable) option, i reckon first solution (all in query string) is a way to deal with pages. But please, normalize query strings (sort (key=value) pairs in alphabet order). This solves "?a=1&b=x" and "?b=x&a=1" differentiation problem.

Answer 3

I use in my projects the following urls:

http://application/products?page=2&sort=+field1-field2

which means - "give me page the second page ordered ascending by field1 and then descending by field2". Or if I need even more flexibility I use:

http://application/products?skip=20&limit=20&sort=+field1-field2

Answer 4

Looking for best practices I came across this site:

http://www.restapitutorial.com

In the resources page there is a link to download a .pdf that contains the complete REST best practices suggested by the author. In which among other things there is a section about pagination.

The author suggest to add support to both using a Range header and using query-string parameters.

Request

HTTP header example:

Range: items=0-24

Query-string parameters example:

GET http://api.example.com/resources?offset=0&limit=25

Where offset is the beginning item number and limit is the maximum number of items to return.

Response

The response should include a Content-Range header indicating how many items are being returned and how many total items exist yet to be retrieved

HTTP header examples:

Content-Range: items 0-24/66

Content-Range: items 40-65/*

In the .pdf there are some other suggestions for more specific cases.

Answer 5

Option 1 seems the best, to the extent that your application views pagination as a technique for producing a different view of the same resource.

Having said that, the URL scheme is relatively insignificant. If you are designing your application to be hypertext-driven (as all REST applications must be by definition), then your client will not be constructing any URIs on its own. Instead, your application will be giving the links to the client and the client will follow them.

One kind of link your client can provide is a pagination link.

The pleasant side-effect of all of this is that even if you change your mind about pagination URI structure and implement something totally different next week, your clients can continue working without any modification whatsoever.

Answer 6

I think the problem with version 3 is more a "point of view" problem - do you see the page as the resource or the products on the page.

If you see the page as the resource it is a perfectly fine solution, since the query for page 2 will always yield page 2.

But if you see the products on the page as the resource you have the problem that the products on page 2 might change (old products deleted, or whatever), in this case the URI is not always returning the same resource(s).

E.g. A customer stores a link to the product list page X, next time the link is opened the product in question might no longer be on page X.