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paginationcouchdblimitoffset

"Previous" link - equivalent of LIMIT x OFFSET y?

I'm creating a page system using CouchDB, showing:

  • 10 items per page
  • a link to the previous page (if any)
  • a link to the next page (if any)

From this article on the topic, I understand that using skip is suboptimal, and that I should instead use the startkey property to specify the first document, read 11 documents from there, display the first 10 and use the key of the 11th to display the link to the next page. What troubles me is the link to the previous page. The article says:

Populating the link to the previous page is as simple as carrying the current startkey over to the next page. If there’s no previous startkey, we are on the first page.

This works when going to the next page: when I move from page 4 to page 5 I can remember that the previous page was 4. But when I move back from page 5 to page 4, I have no way of carrying over the startkey of page 3. How can this work?

Is it possible (and recommended) to use endkey along with skip=10 and limit=1 to find the first element on the previous page, so that I may create a link back to it?

Solution

  • You can in fact only ask for 11 documents with no skip, and that is what Futon does (look at CouchDB logs).

    The trick

    Both the next and previous page link will be similar: startkey is the first or last element, with a skip=1 to avoid overlapping. You then have to correctly use the descending parameter to get previous documents or next documents.

    The execution

    Whenever you're asking for a page, CouchDB answers with eleven documents. Let's say the key of the first one is first and the key of the last one is last. The pagination links will look like:

    "next": /db/_view/myview?descending=true&limit=11&startkey=last&skip=1
"back": /db/_view/myview?descending=false&limit=11&startkey=first&skip=1

    Et voilà! You just have to reverse the documents before displaying them when descending is false. ("Finding your data with views" from the CouchDB guide explains nicely the relation between those parameters and B-Trees.)

    Bonus

    You can easily get the docid of the first or last page (limit=1 and descending true or false), and get a pagination system that looks a lot like something you would have with a classical database (first, last, previous, next).