has_many and class function

Hello,

i have two models :

class Container < ActiveRecord::Base
   has_many :bottles
end

class Bottle < ActiveRecord::Base
   belongs_to :container

   def self.find_all_from_container(container)
     container.bottles.find(:all)
   end
end

i was asking myself if there was a better way to write the function find_all_from_container : i can call it from an instance of Container but how to pass the container instance directly (ie without giving the argument). To replace this :

@container = Container.find(id)
@bottles = Bottle.find_all_from_container(@container)

by something like this :

@container . Container.find(id)
@bottles = @container.bottles.find_all_from_container

Hi,

class Container < ActiveRecord::Base
   has_many :bottles
end

class Bottle < ActiveRecord::Base
   belongs_to :container

   def self.find_all_from_container(container)
     container.bottles.find(:all)
   end
end

...

To replace this :

@container = Container.find(id)
@bottles = Bottle.find_all_from_container(@container)

by something like this :

@container . Container.find(id)
@bottles = @container.bottles.find_all_from_container

has_many gives you what you want for free.

@container.bottles

results in all bottles in the container. No need to call find.

Lutz

I should have add more code in find_all_from_container function. The idea is not to get every entries but to scope entries and perform some actions on them, like :

def self.fill_empty(container)
   bottles = container.bottles.find(:all, :conditions => {:is_empty => true})
   bottles.each {|bottle| bottle.fill}
end

Hi,

Thanks for this help, but i just want to get the container instance in class function to perform various things, regardless of any code in it.

It really helps if you can ask your question with exact code you're using.

actually, there is no code about this, i just want to know if it is possible to get the instance without explicitly giving it in the call.

This is more by curiosity rather than a strict code question.

Hi --

It really helps if you can ask your question with exact code you're
using.

actually, there is no code about this, i just want to know if it is
possible to get the instance without explicitly giving it in the call.

This is more by curiosity rather than a strict code question.

The thing is, the instance is the class object when you call a class
method:

   class C
   end

   def C.greet
     puts "Hi from #{self}"
   end

   C.greet # Hi from C

There's no instance of C involved; you're sending the message directly
to C. A class is (by design) an entirely different object from its
instances (except for constants, which an instance method can refer
to from "below", and except for class variables, which are weird and
quasi-global).

It's possible to engineer things so that a class method can have
access of a sort to an instance via a block. Here's an example (and
if you look at the source code for AR associations, which let you do
things like this, you'll see some much more highly-evolved examples):

   class A
     def self.c_method(&block)
       include Module.new { define_method("m", &block) }
     end
   end

   class B < A
     c_method { puts "Hi; I'm #{self}." }
   end

   B.new.m # Hi; I'm #<B:0x1ea08c>.

It's not exactly what you want, but it might give you some ideas.

David