Belongs_to association doesn't work with _id set

Rails
1

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

2

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

3

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 :slight_smile:

4

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 :slight_smile:

No, sorry. It doesn’t work with has_many :frowning:
And I can’t move the foreign key into Dimension table, so I must find
something else.

5

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

6

Frederick C. 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.

7

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

8

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 L. |
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