Question

The value for @c is a parameter set by the user. If there is a value I would like to query for Cars with that condition. If @c is nil I would like to return all of the Car records.

     @cars = Car.where('car_type = ?', @c)

Answer 1

You can just use a basic check to see if @c is blank:

@cars = @c.blank? ? Car.scoped : Car.where('car_type = ?', @c)