Rails - Jun 2011 - Most idiomatic way to identify and modify an association directly

Suppose that we have Radio Stations which play Songs by means of a License.

======class Song
  has_many :licenses
  has_many :radio_stations, :through => :licenses
end

class RadioStation
  has_many :licenses
  has_many :songs, :through => :licenses
end

class License
  belongs_to :radio_station
  belongs_to :song
end
======
Licenses are either active or not. Given a Song, we want to know which
Licenses are active. If that information was on Song instead, we could
just do something like:

    scope :licensed_for_radio_station, lambda { |rs|
where(:licensed_stations => rs) }

But we can''t, since it''s on License instead. So, two
questions:

    1.) Given a Song, we want to know which Licenses are active.
What''s the most idiomatic way to do this? Association method? Scope?
etc.
    2.) Given a Song and a RadioStation, what''s the most idiomatic way
to find the association that links them?
    3.) Given a Song and a RadioStation, what''s the most idiomatic way
to modify the corresponding license to have :active => true?

Any thoughts are appreciated. Thanks!

~ jf

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John Feminella <johnf@...> writes:
> 
> Suppose that we have Radio Stations which play Songs by means of a License.
> 
> ======> class Song
>   has_many :licenses
>   has_many :radio_stations, :through => :licenses
> end
> 
> class RadioStation
>   has_many :licenses
>   has_many :songs, :through => :licenses
> end
> 
> class License
>   belongs_to :radio_station
>   belongs_to :song
> end
> ======> 
> Licenses are either active or not. Given a Song, we want to know which
> Licenses are active. If that information was on Song instead, we could
> just do something like:
> 
>     scope :licensed_for_radio_station, lambda { |rs|
> where(:licensed_stations => rs) }
> 
> But we can''t, since it''s on License instead. So, two
questions:
> 
>     1.) Given a Song, we want to know which Licenses are active.
> What''s the most idiomatic way to do this? Association method?
Scope?
> etc.
>     2.) Given a Song and a RadioStation, what''s the most idiomatic
way
> to find the association that links them?
>     3.) Given a Song and a RadioStation, what''s the most idiomatic
way
> to modify the corresponding license to have :active => true?
> 
> Any thoughts are appreciated. Thanks!
> 
> ~ jf
> 

Since licenses can either be active or deactive, I assume there is a
boolean field behind it, in which case a scope would be handy:

class License
  belongs_to :radio_station
  belongs_to :song
  scope :activated, where => :active = true
end

This should allow you to perform the following:

song = Song.first
licences_for_song = song.licences.active

or even

licensed_stations = song.licences.activated.radio_stations

If you already have the radio station, finding of it is listed should be
easy:

licensed_stations.include? radio_station

The last issue is a little more complex, but I think something along the
lines of:

License.where(:song => song).where(:radio_station =>
radio_station).activate!

Then create a method to respond (I am assuming the combined keys are
unique):

class License
  belongs_to :radio_station
  belongs_to :song
  scope :activated, where => :active = true

  def activate!
    update_attribute :active, true
  end
end

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Andrew Skegg <andrewskegg@...> writes:

Sorry,this is slightly wrong:
> song = Song.first
> licences_for_song = song.licences.active
It should be:

licences_for_song = song.licences.activated

And this can be optimised if you do not need all the licenses:
 
> licensed_stations.include? radio_station
To:

license = song.licences.activated.where(:radio_station = radio_station)





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