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Rodrigo Lueneberg

2008-Jun-14 13:58 UTC

Active Record Insert relationship

I need help inserting an address record to a tabled called realestates.
The relationship between these to tables is 1 to 1.

- realestates table has an address_id field set to not NULL

class Address < ActiveRecord::Base
end

class RealEstate < ActiveRecord::Base
  has_one :address
end

I created two objects to match these two tables. When I let rails do the
insert of RealEstate I get an error stating that address_id is NULL.
This means that I would need to insert the address first before
inserting the RealEstate record to avoid this problem. But if Real
Estate is new record it does not have an id yet and I can''t do
that. One option is to remove the constraint NOT NULL I don''t want to
do
that.

So the logical order would be first create an instance variable for
RealEstate and do the insert. Second, create and instance variable for
address and do the insert like below.

@real_estate = RealEstate.new(params[:real_estate])
@address = Address.new(params[:address])

But how do I solve the fact that address_id cannot be NULL on
realestates? Am I missing something?

Rod
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Frederick Cheung

2008-Jun-14 15:32 UTC

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Re: Active Record Insert relationship

On Jun 14, 2:58 pm, Rodrigo Lueneberg <rails-mailing-l...@andreas-
s.net> wrote:>
> @real_estate = RealEstate.new(params[:real_estate])
> @address = Address.new(params[:address])
>
> But how do I solve the fact that address_id cannot be NULL on
> realestates? Am I missing something?
@address.build_real_estate(...) ?

Fred>
> Rod
> --
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Rick DeNatale

2008-Jun-15 12:43 UTC

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Re: Active Record Insert relationship

On Sat, Jun 14, 2008 at 9:58 AM, Rodrigo Lueneberg <
rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>
> I need help inserting an address record to a tabled called realestates.
> The relationship between these to tables is 1 to 1.
>
> - realestates table has an address_id field set to not NULL
>
> class Address < ActiveRecord::Base
> end
>
> class RealEstate < ActiveRecord::Base
>  has_one :address
> end
>
> I created two objects to match these two tables. When I let rails do the
> insert of RealEstate I get an error stating that address_id is NULL.
>
You appear to have a misconception about the relationship between
has_one/has_many and the db schema.

First, you need to declare a belongs_to relation to the
''owning'' class in
the owned class, so you need

class Address < ActiveRecord::Base
   belongs_to :real_estate
end

class RealEstate < ActiveRecord::Base
  has_one :address
end

Second, the has_x associations don''t require or use a foreign key field
in
the table of the class which has related objects, it''s the other way
around.  The belongs_to association requires that the table of the class
which belongs_to another has a foreign key pointing to an instance of the
owning class.  So with the above declarations the addresses table should
have a real_estate_id field not the other way around.

If you really want to have an address_id in the real_estates table then you
should instead declare that RealEstate belongs_to Address, and Address
has_one RealEstate.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

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Rodrigo Lueneberg

2008-Jun-15 15:38 UTC

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Re: Active Record Insert relationship

thanks, I did change Address to include belongs_to. But I still get the 
error:
Mysql::Error: Column ''address_id'' cannot be null: INSERT INTO 
`real_estates`
Should I create a address object, reference the realestate from it and 
save the address object which I assume would create a new real_estate 
record? something like this:

@address = Address.new(params[:address])
@address.realestate = RealEstate.new(params[:real_estate])

instead of

@real_estate = RealEstate.new(params[:real_estate])
@real_estate.address = Address.new(params[:address])

this is the code below:

class Address < ActiveRecord::Base
  belongs_to :real_estate
end

class RealEstate < ActiveRecord::Base
  has_one :address
end



class Admin::RealestateController < ApplicationController

  def index
    render :text => "Real Estate"
  end

  def new
    render(:action => ''new'')
  end

  def create
    @real_estate = RealEstate.new(params[:real_estate])
    @real_estate.address = Address.new(params[:address])

    if @real_estate.save
      render :text => "Saved"
    else
      render(:action => ''new'')
    end
  end
end



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Rick DeNatale

2008-Jun-15 17:20 UTC

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Re: Active Record Insert relationship

On Sun, Jun 15, 2008 at 11:38 AM, Rodrigo Lueneberg <
rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>
> thanks, I did change Address to include belongs_to. But I still get the
> error:
> Mysql::Error: Column ''address_id'' cannot be null: INSERT
INTO
> `real_estates`

Go back and re-read what I posted carefully.

> this is the code below:
>
> class Address < ActiveRecord::Base
>  belongs_to :real_estate
>
This declares that the addresses table should have a column called
real_estate_id.

If you have an address object and have to fetch the corresponding
real_estate, then an SQL query

   select * from real_estates where id = self.real_estate_id

end

class RealEstate < ActiveRecord::Base
 has_one :address

This does NOT imply that the real_estates table has a column, called
address_id.

If you have an instance of RealEstate and need to get the corresponding
address then the SQL query will be something like:

  select * from addresses limit 1 where real_estate_id = self.id
>
> end
>
If you really want the id of the Address in the RealEstate you need to set
up the associations so that RealEstate belongs_to Address, and Address
has_one RealEstate, which is the reverse of what you have declared.

You also need to make sure that the object with the has_x attribute is saved
before the one which belongs_to it. This is because the belongs to object
needs the id of the owner, and there won''t be one until the owner is
saved.



Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

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Rodrigo Lueneberg

2008-Jun-16 22:05 UTC

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Re: Active Record Insert relationship

Perfect. I am trying it out this weekend. Thank you.
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