Active Record Insert relationship

Rails
1

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

2

On Jun 14, 2:58 pm, Rodrigo L. <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

3

On Sat, Jun 14, 2008 at 9:58 AM, Rodrigo L. <
[email protected]> wrote:

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/

4

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

5

On Sun, Jun 15, 2008 at 11:38 AM, Rodrigo L. <
[email protected]> 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/

6

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