MongoDB infinite scroll sorted results
mongodb, ruby-on-rails-3
Solution
There's a few ways to do this with MongoDB. You can use the `.skip()` and `.limit()` commands (documented here: http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-CursorMethods) to apply pagination to the query.
Alternatively, you could add a clause to your query like: `{sorted_field : {$gt : <value from last record>}}`. In other words, filter out matches of the query whose sorted value is less than that of the last resulting item from the current page of results. For example, if page 1 of results returns documents A through D, then to retrieve the next page 2 you repeat the same query with the additional filter `x > D`.
Problem
I am having a problem trying to achieve the following: I'd like to have a page with 'infinite' scrolling functionality and all the results fetched to be sorted by certain attributes. The way the code currently works is, it places the query, sorts the results, and displays them. The problem is, that once the user reaches the bottom of the page and new query is placed, the results from this query are sorted, but in its own context. That is, if you have a total of 100 results, and the first query display only 50, then they are sorted. But the next query (for the next 50) sorts the results only based on these 50 results, not based on the 100 (total results). So, do I have to fetch all the results at once, sort them, and then apply some pagination logic to them or there's a way for MongoDB to actually have infinite scrolling (AJAX requests) with sorting applying to the results?