Enterprise Rails

Basing a Model on a View

Basing a model on a view is actually straightforward. The syntax is the same as it would be for a normal table. For the current_movie_showtimes table, our CurrentMovieShowtime class is defined like this:

class CurrentMovieShowtime < ActiveRecord::Base
  belongs_to :movie
  belongs_to :theatre
  belongs_to :auditorium, :foreign_key => [:room, :theatre_id]
end

We also define the inverse relationships in the related classes. For example, in the Movie class, we have associations to both the MovieShowtime class as well as the CurrentMovieShowtime class:

class Movie < ActiveRecord::Base
  has_many :movie_showtimes, :dependent => :destroy
  has_many :current_movie_showtimes
end

The difference is that the relationship defined with the view cannot have a destroy dependency defined. You can only modify views by modifying the tables they depend on, so deleting from them would be meaningless (it would also cause an error).

The rest of the ActiveRecord magic still applies. You can access current showtimes directly through an association. For example:

cool_movie.current_movie_showtimes

You can also use all of the automatically defined ActiveRecord accessor on the CurrentMovieShowtime class itself as well:

CurrentMovieShowtime.find_all_by_theatre_id(@theatre.id)

Our original example of finding “current movies in my area” is now much simpler as well:

CurrentMovieShowtime.find(:all, :conditions => [' miles_between_lat_long( current_movie_showtimes.lat, current_movie_showtimes.long, ?, ? ) < ...