ActiveRecord::Relation size vs count

An array in ruby has 3 methods that do the same thing. size, count, and length all return the number of items in an array.

An ActiveRecord::Relation however uses them a bit differently. count is always going to run a query in the database while size will return the number of items in the collection based on the objects currently in the object graph.

> songs  = Songs.all
> songs.size
10
> songs.count
SELECT count(*) FROM songs;
10