Question

My goal is to return a single object in a Rails Active Record query. I want to retrieve the most recent record when the table is sorted by the created_at date. So, in the example below, that means I want to return the record with the ID of 2. I don’t understand why the 4 queries below all return the same result?

Sales Table Records

 +----+---------+-------+------------+----------------------------+
 | ID | user_id | price | sale_date  |         created_at         |
 +----+---------+-------+------------+----------------------------+
 |  1 |       1 |   200 | 2012-08-07 | 2012-10-02 23:01:46.706727 |
 |  2 |       1 |   400 | 2009-05-11 | 2012-10-02 23:09:01.342879 |
 +----+---------+-------+------------+----------------------------+

Queries:

 <%= current_user.sales.order("created_at").last.price %>

returns: 200

 <%= current_user.sales.order("created_at DESC").last.price %>

returns: 200

 <%= current_user.sales.order("created_at ASC").last.price %>

returns: 200

 <%= current_user.sales.last.price %>

returns: 200

I also tried:

 <%= current_user.sales.last("created_at").price %>

returns: undefined method 'assert_valid_keys' for "created_at":String

Answer 1

If the Sale class has a default_scope defined, and it includes an order clause, then you may use

.reorder("created_at DESC")

instead of

.order("created_at DESC")