Active Record sorting using Ruby sort function

I have a query of the form


and I would like to have the result sorted in a particular way. The comparision function for the sort is complex and can't be expressed by simply ordering ascendingly or descendingly on the fields, but depends on a complex term based on fields from both :parents and :children.

I currently use the following approach:

  ordered_result=result.to_a.sort { |a,b| my_sort_function(a,b) }

I am aware that this means that all the records have to be present in memory. If there is an easy way to avoid this, it would be nice, but since I can ensure (from the context of the application), that the number of records returned from the query is always smaller than a certain, system-wide constant (currently 250), this is not a real problem.

However, I wonder whether my approach to convert the ActiveRecord::Relation to an array is a good idea. Maybe there is a better way to implement sorting?