Chapter 11. View-Backed Models
Some concepts are extremely easy to explain in words, yet difficult to extract from a database. For example, on a ticket-purchasing site, itâs pretty obvious that you need a way to quickly show visitors âcurrent movies in my area.â That is certainly an easy concept, but letâs examine what it takes to get that kind of information out of our database.
âCurrentâ means we need to be looking in the movie_showtimes
table. We might define current
to mean movies starting within a week.
Knowing the showtime isnât enough. We need to get the movie information, too. A showtime without the movie name isnât very useful. While weâre at it, we probably need to know the rating and the length of the movie as well.
The request âin my areaâ means we need to know where the visitor is
and where the movie theatre is. We can use the PL/pgSQL distance procedure miles_between_lat_long
that we wrote in Chapter 6, but to do so we need data
from the theatres
table (the zip code)
and from the zip_codes
table (the
latitude and longitude).
This represents a query with four tables: movie_showtimes
, theatres
, movies
, and zip_codes
. We could write
an ActiveRecord query that could get us what we want:
MovieShowtime.find(:all, :include => [:movie, :theatre], :conditions => " movie_showtimes.start_time - now() < '1 week'::interval and movie_showtimes.start_time > now() " )
The first problem we notice, as far as ActiveRecord die-hards are concerned, is that weâve got ...
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