%w(hashrockets spaceships bangbangs)

> non-optimized bits & pieces <

Falling in Love With AR's Scoping

If you do activerecord, you should fall in love with scoping, as it can really boast ur AR-fu.

Here’s an example:

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class Shirt
  belongs_to :owner, :polymorphic => true
end

class Cat
  has_many :shirts, :as => :owner
end

class Dog
  has_many :shirts, :as => :owner
end

Let’s say i want to be able to retrieve doggie’s red shirts:

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class Dog
  # (blah blah)

  def red_shirts
    shirts.where(:color => 'red')
  end
end

doggie.shirts     # all shirts
doggie.red_shirts # all red shirts

Ok, what if we want to retrieve kitty’s red shirts as well ?

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class Cat
  # (blah blah)

  def red_shirts
    shirts.where(:color => 'red')
  end
end

kitty.shirts     # all shirts
kitty.red_shirts # all red shirts

Hmmm, duplication detected, but not so bad (yet) .. how abt i want to retrieve all red shirts ? AR supports this via the scope declarative:

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class Shirt
  # (blah blah)

  scope :red, where(:color => 'red')

  # * A less DSL-ish approach is to declare a class method
  # def self.red
  #   where(:color => 'red')
  # end
end

Shirt.red # all red shirts

And you know what, with the new Shirt.red, i can throw away Cat#red_shirts & Dog#red_shirts. If i ever want to fetch the red shirts of doggie & kitty:

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doggie.shirts     # all doggie's shirts
doggie.shirts.red # all doggie's red shirts

kitty.shirts      # all kitty's shirts
kitty.shirts.red  # all kitty's red shirts

And to make it even sweeter, i can do the following as well:

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doggie.shirts.red.create(:size => :xl) # doggie gets a new red :xl shirt
kitty.shorts.red.create(:size => :xs)  # kitty gets a new red :xs shirt

Honestly, we should love AR’s scoping rite ?!

If u have the time, take a look at the activerecord doc.

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