This was a gotcha for me. reverse_params! is generally used to set default values on a hash. In the case of the params hash, that is accessible in the controller from an http action, it uses stringed keys and not symbolic keys. The following wasn’t working correctly because my resulting hash had two page keys set; one as a stringed key and one as a symbolic key.

BROKEN SCENARIO: original params hash is the following: {‘page’=>‘2’} params.reverse_merge!( :page => 1, :sort_by => ‘new’, :view_by => ‘all’ ) result: {:page => 1, :sort_by => ‘new’, :view_by => ‘all’ , ‘page’=>‘2’}

CORRECT SCENARIO: original params hash is the following: {‘page’=>‘2’} params.reverse_merge!( ‘page’ => 1, ‘sort_by’ => ‘new’, ‘view_by’ => ‘all’ ) result: {‘page’ => 1, ‘sort_by’ => ‘new’, ‘view_by’ => ‘all’}

Trying to access the :page in the first scenario gives you a value of 1, set by the default values, where you really want 2, passed in to the controller.