Ruby on Rails / will_paginate：按自定义列排序

Question

I've got a rather complicated SQL-Query whose results should be paginated and displayed to the user. I don't want to go into details here, but to put it simple I just select all columns of a model, and an additional column , that is used just for sorting purposes.

Note.select( ['notes.*', "<rather complicated clause> AS 'x'"] ).joins(...)...

After some .join()'s and a .group() , I finally call .order() and .paginate on the relation. If I order by any of the model's natural columns everything works fine, if I however order by the "artificial" column x , rails gives me the error:

no such column: x

This seems to occur because will_paginate seems to do a COUNT(*) -statement before getting the actual data, simply to get the amounts of data it has to process. This COUNT(*) -statement is (of course) generated from the original statement, which includes the ORDER BY x . The problem now is, that will_paginate keeps the ORDER BY in the statement but simply replaces the column definitions with COUNT(*) and thus cannot find the column x .

Using Rails 3 and will_paginate 3.0.pre2 .

Is there any way to get around this?

thx for any help

Answer 1

You can disable the initial count query by passing in the value manually:

total_entries = Note.select(...).joins(...).count
Note.select( ... ).joins(...).group().paginate(:total_entries => total_entries)

The above is not a literal code sample and you may need to tweak your count query to get the correct results for your join. This should let you do a straight up complex query on the pagination.