Question

I’ve populated a hash with two different models. I then try to sort them like so:

@search_results = User.find(:all, :conditions => ['name LIKE ?', "%#{params[:query]}%"])
@search_results += Book.find(:all, :conditions => ['title LIKE ?', "%#{params[:query]}%"])
@search_results.sort! { |a,b| a.impressions_count <=> b.impressions_count }

This throws the following error:

comparison of User with Book failed

Both users and books have an integer-based impressions_count. Why can’t I sort via this attribute? What other options do I have?

Answer 1

I faced a similar problem recently and ended up writing some custom sql because all other ways returned an array. Pretty sure its not a good idea to use the sort method since it will always be more efficient to sort in SQL than ruby, especially when the data set gets large

  @combined_results = User.find_by_sql(["SELECT title, id, impressions_count, NULL as some_attribute_of_book
                                         FROM user
                                         WHERE title LIKE ?
                                         UNION SELECT title, id, impressions_count, some_attribute_of_book FROM book 
                                         WHERE title LIKE ?
                                         ORDER BY impressions_count", params[:query], params[:query]])

The above is completely untested code, more of an example than anything