Rails - Nov 2009 - Overriding initialize in active_record Model or after_initialize

Hi,

I am trying to set initial process when instantiating model by  
overriding initialize() method which takes arguments. The initialize()  
method overrides the parent ActiveRecord::Base class''s by taking  
arguments and assign arguments to its instance variables.

class Product < ActiveRecord::Base

   def initialize(item = nil)
     super
     # and then process to assign variables from item argument to  
instance variables
     # ....
   end

In order to fully leverage ActiveRecord::Base class functionality, I''m
calling super to run the default initialization process (i.e. set up  
all setter/getter methods). However, the Product class above still  
can''t find getter/setter methods for its variables. In the meantime, I
found the following blog article suggesting use after_initialize  
instead of overriding Active Record object.

Rails: Don''t override initialize on ActiveRecord objects
http://blog.dalethatcher.com/2008/03/rails-dont-override-initialize-on.html

I could not find ways to set arguments for this after_initialize  
approach.

Can anybody advise should I override initialize() or use  
after_initialize with some ways to take arguments?

Thanks,
Ryo
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On Nov 8, 8:04 am, Ryoichiro Kamiya
<ryoichiro.kam...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
>
> I am trying to set initial process when instantiating model by  
> overriding initialize() method which takes arguments. The initialize()  
> method overrides the parent ActiveRecord::Base class''s by taking  
> arguments and assign arguments to its instance variables.
>
> class Product < ActiveRecord::Base
>
>    def initialize(item = nil)
>      super
>      # and then process to assign variables from item argument to  
> instance variables
>      # ....
>    end

What does the actual code in there look like? What is the error that
you get ?

Fred
>
> In order to fully leverage ActiveRecord::Base class functionality,
I''m  
> calling super to run the default initialization process (i.e. set up  
> all setter/getter methods). However, the Product class above still  
> can''t find getter/setter methods for its variables. In the
meantime, I  
> found the following blog article suggesting use after_initialize  
> instead of overriding Active Record object.
>
> Rails: Don''t override initialize on ActiveRecord
objectshttp://blog.dalethatcher.com/2008/03/rails-dont-override-initialize-o...
>
> I could not find ways to set arguments for this after_initialize  
> approach.
>
> Can anybody advise should I override initialize() or use  
> after_initialize with some ways to take arguments?
>
> Thanks,
> Ryo

Thanks Fred.

I got the following error.
NoMethodError in ProductsController#search
undefined method `stringify_keys!'' for
#<Amazon::Element:0x10373c6a8>
/Library/User/Gems/1.8/gems/activerecord-2.3.3/lib/active_record/
base.rb:2731:in `attributes=''
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.3/lib/active_record/
base.rb:2434:in `initialize''
/Users/User/Documents/Aptana Studio Workspace/Flatworld/app/models/
product.rb:5:in `initialize''
/Users/User/Documents/Aptana Studio Workspace/Flatworld/app/models/
products.rb:31:in `new''
.... [more]

and actual code for the model class is:
----------------------------------------------------------------
class Product < ActiveRecord::Base
  has_many :inventories

  def initialize(item)
    super
    @amazon_asin = item.get(''asin'')
    @manufacturer = item.get(''itemattributes/manufacturer'')
    @name = item.get(''itemattributes/title'')
    @releasedate = item.get(''itemattributes/releasedate'')
    @amazon_url = item.get(''detailpageurl'')
    @amazon_image = item.get_hash(''smallimage'')
  end
----------------------------------------------------------------
item is the result from Amazon API search result. I am trying to
instantiate Product class with the result data set.
Is this right approach to instantiate model class by overriding
initialize method with super method within?

Ryo


On 11月8日, 午後6:27, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Nov 8, 8:04 am,
RyoichiroKamiya<ryoichiro.kam...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
>
> > Hi,
>
> > I am trying to set initial process when instantiating model by  
> > overriding initialize() method which takes arguments. The initialize()
 
> > method overrides the parent ActiveRecord::Base class''s by
taking  
> > arguments and assign arguments to its instance variables.
>
> > class Product < ActiveRecord::Base
>
> >    def initialize(item = nil)
> >      super
> >      # and then process to assign variables from item argument to  
> > instance variables
> >      # ....
> >    end
>
> What does the actual code in there look like? What is the error that
> you get ?
>
> Fred
>
>
>
> > In order to fully leverage ActiveRecord::Base class functionality,
I''m  
> > calling super to run the default initialization process (i.e. set up  
> > all setter/getter methods). However, the Product class above still  
> > can''t find getter/setter methods for its variables. In the
meantime, I  
> > found the following blog article suggesting use after_initialize  
> > instead of overriding Active Record object.
>
> > Rails: Don''t override initialize on ActiveRecord
objectshttp://blog.dalethatcher.com/2008/03/rails-dont-override-initialize-o...
>
> > I could not find ways to set arguments for this after_initialize  
> > approach.
>
> > Can anybody advise should I override initialize() or use  
> > after_initialize with some ways to take arguments?
>
> > Thanks,
> > Ryo

On Nov 14, 10:05 am, Ryo
<ryoichiro.kam...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> and actual code for the model class is:
> ----------------------------------------------------------------
> class Product < ActiveRecord::Base
>   has_many :inventories
>
>   def initialize(item)
>     super
>     @amazon_asin = item.get(''asin'')
>     @manufacturer =
item.get(''itemattributes/manufacturer'')
>     @name = item.get(''itemattributes/title'')
>     @releasedate = item.get(''itemattributes/releasedate'')
>     @amazon_url = item.get(''detailpageurl'')
>     @amazon_image = item.get_hash(''smallimage'')
>   end
> ----------------------------------------------------------------
> item is the result from Amazon API search result. I am trying to
The reason this isn''t working is that

super

does not mean ''call the superclass implementation with no
arguments'' (which is fine in this case - Active Record just
won''t set
any attributes). It means ''call the super class implementation with
the same arguments'', so you''re passing this an amazon search
result
object to a method expecting a hash. You can force the superclass to
be called with no arguments by doing super().

I assume that you''re trying to set activerecord attributes for the
title and so on. If so, use the accessor functions (ie
self.amazon_asin = ... ). Active Record doesn''t store its attributes
in instance variables, so what you''re doing won''t work.

Lastly while you can make the above work, I think that you''ll be
making life for yourself more difficult by requiring that Products be
initialized with an amazon search result object (eg for creating
objects in tests). another approach is to leave initialize alone and
write


class Product < ...

  def self.from_amazon_search_result(item)
    new :amazon_asin => item.get(''asin''), :manufacturer
=>  item.get
(''itemattributes/manufacturer'') , ...
  end
end

Fred

It worked perfect as you suggested using class method
"self.from_amazon_search_result".
Does this mean I am instantiating Product object by this new class
method rather than new()?
Sorry this is new approach to me, and I just would like to know for my
learning.
> Active Record doesn''t store its attributes in instance variables,
so what you''re doing won''t work.
This was also new to me. I was building it on my belief that every
instance of AR-extending class holds its attributes in instance
variable. I will look for some specs on web just so I learn!

Thanks again Fred!

On 11月14日, 午後7:07, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Nov 14, 10:05 am, Ryo
<ryoichiro.kam...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> > and actual code for the model class is:
> > ----------------------------------------------------------------
> > class Product < ActiveRecord::Base
> >   has_many :inventories
>
> >   def initialize(item)
> >     super
> >     @amazon_asin = item.get(''asin'')
> >     @manufacturer =
item.get(''itemattributes/manufacturer'')
> >     @name = item.get(''itemattributes/title'')
> >     @releasedate =
item.get(''itemattributes/releasedate'')
> >     @amazon_url = item.get(''detailpageurl'')
> >     @amazon_image = item.get_hash(''smallimage'')
> >   end
> > ----------------------------------------------------------------
> > item is the result from Amazon API search result. I am trying to
>
> The reason this isn''t working is that
>
> super
>
> does not mean ''call the superclass implementation with no
> arguments'' (which is fine in this case - Active Record just
won''t set
> any attributes). It means ''call the super class implementation
with
> the same arguments'', so you''re passing this an amazon
search result
> object to a method expecting a hash. You can force the superclass to
> be called with no arguments by doing super().
>
> I assume that you''re trying to set activerecord attributes for the
> title and so on. If so, use the accessor functions (ie
> self.amazon_asin = ... ). Active Record doesn''t store its
attributes
> in instance variables, so what you''re doing won''t work.
>
> Lastly while you can make the above work, I think that you''ll be
> making life for yourself more difficult by requiring that Products be
> initialized with an amazon search result object (eg for creating
> objects in tests). another approach is to leave initialize alone and
> write
>
> class Product < ...
>
>   def self.from_amazon_search_result(item)
>     new :amazon_asin => item.get(''asin''),
:manufacturer =>  item.get
> (''itemattributes/manufacturer'') , ...
>   end
> end
>
> Fred