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Alessandro Re

2007-Oct-08 10:01 UTC

belongs_to association doesn''t work with _id set

Hello there,
I''m developing an application which has models like this:

class Vehicle < ActiveRecord::Base
    belongs_to :internal_dim, :class_name => "Dimension"

    def before_create()
        idim = Dimension.create
        self.internal_dim_id = idim.id
        #self.create_internal_dim # Doesn''t work
    end
end

class Dimension < ActiveRecord::Base
    has_one :vehicle
end

That is, creating the vehicle should create a dimension entry (yeah, i
know it''s strange, but actually dimension table is shared among
different things, so the relationship is inverted).

Anyway, it happens that when a vehicle is created, the internal
dimension id is correctly set:
>>> v = Vehicle.create
>>> v.internal_dim_id=> 3

But the method doesn''t get the corresponding value:
>>> v.internal_dim=> nil

While the records exists:
>> Dimension.find(v.internal_dim_id)=> #<Dimension:0xb7042678 @attributes={blah}>

Have you any idea?
Thanks

~~Ale
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Roderick van Domburg

2007-Oct-08 10:53 UTC

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Re: belongs_to association doesn''t work with _id set

Alessandro Re wrote:> Hello there,
> I''m developing an application which has models like this:
> 
> class Vehicle < ActiveRecord::Base
>     belongs_to :internal_dim, :class_name => "Dimension"
> 
>     def before_create()
>         idim = Dimension.create
>         self.internal_dim_id = idim.id
>         #self.create_internal_dim # Doesn''t work
>     end
> end
> 
> class Dimension < ActiveRecord::Base
>     has_one :vehicle
> end
> 
> That is, creating the vehicle should create a dimension entry (yeah, i
> know it''s strange, but actually dimension table is shared among
> different things, so the relationship is inverted).
> 
> Anyway, it happens that when a vehicle is created, the internal
> dimension id is correctly set:
> 
>>>> v = Vehicle.create
>>>> v.internal_dim_id
> => 3
> 
> But the method doesn''t get the corresponding value:
> 
>>>> v.internal_dim
> => nil
> 
> While the records exists:
> 
>>> Dimension.find(v.internal_dim_id)
> => #<Dimension:0xb7042678 @attributes={blah}>
> 
> Have you any idea?
It''s because of the has_one in Dimension. It causes the reference to be
held by the other object. Either change it into has_many or move the 
foreign key column over to the Dimension table.

--
Roderick van Domburg
http://www.nedforce.com
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Alessandro Re

2007-Oct-08 11:24 UTC

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Re: belongs_to association doesn''t work with _id set

Roderick van Domburg wrote:> It''s because of the has_one in Dimension. It causes the reference
to be
> held by the other object. Either change it into has_many or move the 
> foreign key column over to the Dimension table.
Argh! You''re right!
Thanks very much :)
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Alessandro Re

2007-Oct-08 13:10 UTC

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Re: belongs_to association doesn''t work with _id set

Alessandro Re wrote:> Roderick van Domburg wrote:
>> It''s because of the has_one in Dimension. It causes the
reference to be
>> held by the other object. Either change it into has_many or move the 
>> foreign key column over to the Dimension table.
> 
> Argh! You''re right!
> Thanks very much :)
No, sorry. It doesn''t work with has_many :(
And I can''t move the foreign key into Dimension table, so I must find 
something else.
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Frederick Cheung

2007-Oct-08 13:14 UTC

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Re: belongs_to association doesn''t work with _id set

On 8 Oct 2007, at 11:01, Alessandro Re wrote:
>
> Hello there,
> I''m developing an application which has models like this:
>
> class Vehicle < ActiveRecord::Base
>     belongs_to :internal_dim, :class_name => "Dimension"
>
>     def before_create()
>         idim = Dimension.create
>         self.internal_dim_id = idim.id
>         #self.create_internal_dim # Doesn''t work
>     end
> end
Why not self.internal_dim = idim ?

Fred

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Alessandro Re

2007-Oct-08 13:24 UTC

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Re: belongs_to association doesn''t work with _id set

Frederick Cheung wrote:> On 8 Oct 2007, at 11:01, Alessandro Re wrote:
> 
>>         #self.create_internal_dim # Doesn''t work
>>     end
>> end
> 
> Why not self.internal_dim = idim ?
> 
> Fred
I found out that it doesn''t work: after the assignment the 
internal_dim_id is nil.

Look: the actual code:

def before_create()
    idim = Dimension.create
    edim = Dimension.create
    self.internal_dim_id = idim.id
    self.external_dim_id = edim.id

    puts("  Dimensions: int #{internal_dim_id} ext
#{external_dim_id}")
end

output:

#<Company:0xb711d494> created
#<Dimension:0xb70d02e8> created
#<Dimension:0xb70c8480> created
  Dimensions: int 1 ext 2

Changing with:

def before_create()
    idim = Dimension.create
    #edim = Dimension.create
    self.internal_dim_id = idim.id
    #self.external_dim_id = edim.id
    #self.create_internal_dim
    self.create_external_dim
    puts("  Dimensions: int #{internal_dim_id} ext
#{external_dim_id}")
end

output:

#<Company:0xb713510c> created
#<Dimension:0xb70ebd04> created
#<Dimension:0xb70e5634> created
  Dimensions: int 1 ext

As you see, external dim id is not set, even if the dimension is 
created. I didn''t figure out why this happen, yet.
But this is a minimal issue for me now, I need to understand before why 
internal_dim doesn''t return the associated dimension, even if the id is
set.
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Alessandro Re

2007-Oct-08 14:21 UTC

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Re: belongs_to association doesn''t work with _id set

Ok, solved. The problem was that
> class Vehicle < ActiveRecord::Base
>     belongs_to :internal_dim, :class_name => "Dimension"
doesn''t set automatically the foreign key to internal_dim_id when 
class_name is used. So, with
>     belongs_to :internal_dim, :foreign_key =>
"internal_dim_id", :class_name => "Dimension"
it works, and probably (didn''t try yet), it will fix the assignment 
problems:
>>         #self.create_internal_dim # Doesn''t work
> Why not self.internal_dim = idim ?
and also
>>   self.create_intternal_dim
Thanks guys, hope this will help someone in future

~~Aki
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Jay Levitt

2007-Oct-08 14:37 UTC

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Re: belongs_to association doesn''t work with _id set

On Mon, 8 Oct 2007 16:21:06 +0200, Alessandro Re wrote:
> Ok, solved. The problem was that
> 
>> class Vehicle < ActiveRecord::Base
>>     belongs_to :internal_dim, :class_name => "Dimension"
> 
> doesn''t set automatically the foreign key to internal_dim_id when 
> class_name is used. So, with
IIRC that is fixed with 2.0.  Yay.

-- 
Jay Levitt                |
Boston, MA                | My character doesn''t like it when they
Faster: jay at jay dot fm | cry or shout or hit.
http://www.jay.fm         | - Kristoffer 


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