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Fabien Jakimowicz

2007-Aug-02 09:40 UTC

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

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Lutz Horn

2007-Aug-02 10:02 UTC

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Re: has_many and class function

Hi,

2007/8/2, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>:> 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

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Fabien Jakimowicz

2007-Aug-02 10:09 UTC

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Re: has_many and class function

On Aug 2, 2007, at 12:02 PM, Lutz Horn wrote:
>
> Hi,
>
> 2007/8/2, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>:
>> 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.
>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

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Lutz Horn

2007-Aug-02 10:13 UTC

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Re: has_many and class function

Hi,

2007/8/2, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>:> 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
You can do this by using select:

container.bottles.select { |bottle| bottle.is_empty }

The block given to select must return true for every object to be
included in the resulting list.

Lutz

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Fabien Jakimowicz

2007-Aug-02 10:19 UTC

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Re: has_many and class function

On Aug 2, 2007, at 12:13 PM, Lutz Horn wrote:
>
> Hi,
>
> 2007/8/2, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>:
>> 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
>
> You can do this by using select:
>
> container.bottles.select { |bottle| bottle.is_empty }
>
> The block given to select must return true for every object to be
> included in the resulting list.
>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.


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Pratik

2007-Aug-02 10:22 UTC

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Re: has_many and class function

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

On 8/2/07, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>
wrote:>
> On Aug 2, 2007, at 12:02 PM, Lutz Horn wrote:
>
> >
> > Hi,
> >
> > 2007/8/2, Fabien Jakimowicz
<fabien-SKT9N6NoqVlE4Z/KZFzVqg@public.gmane.org>:
> >> 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.
> >
> 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
>
> >
>

-- 
Cheers!
- Pratik
http://m.onkey.org

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Fabien Jakimowicz

2007-Aug-02 10:28 UTC

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Re: has_many and class function

On Aug 2, 2007, at 12:22 PM, Pratik wrote:
>
> 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.




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dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2007-Aug-02 12:20 UTC

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Re: has_many and class function

Hi --

On Thu, 2 Aug 2007, Fabien Jakimowicz wrote:
>
> On Aug 2, 2007, at 12:22 PM, Pratik wrote:
>
>>
>> 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

-- 
* Books:
   RAILS ROUTING (new! http://www.awprofessional.com/title/0321509242)
   RUBY FOR RAILS (http://www.manning.com/black)
* Ruby/Rails training
     & consulting:  Ruby Power and Light, LLC (http://www.rubypal.com)

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