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Michael Henry

2006-Dec-13 14:03 UTC

Assigning objects...

I''m a Ruby Newbie (hey that rhymes!) and I suspect I haven''t
understood
the syntax properly.
I''m trying to assign one ActiveRecord object to the field of another
and
I think this should work:

 >> org = Organisation.new
=> #<Organisation:0xb7652dd8 @new_record=true, 
@attributes={"fax_number"=>nil, "postal_address"=>nil,
"name"=>nil,
"org_structure_id"=>0, "location_address"=>nil,
"tin"=>nil,
"phone_number"=>nil, "contact"=>nil,
"email_address"=>nil}>
 >> org.name = "Aces High Inc."
=> "Aces High Inc."
 >> person = NaturalPerson.new
=> #<NaturalPerson:0xb764997c @new_record=true, 
@attributes={"postal_address"=>nil, "fax_number"=>nil,
"name"=>nil,
"dob"=>nil, "phone_number"=>nil,
"visa"=>nil, "mobile_number"=>nil,
"email_address"=>nil, "nationality"=>nil}>
 >> person.name = "Fred Flinstone"
=> "Fred Flinstone"
 >> org.contact << person
NoMethodError: You have a nil object when you didn''t expect it!
You might have expected an instance of Array.
The error occured while evaluating nil.<<
        from (irb):13

My Organisation model looks like this:

class Organisation < ActiveRecord::Base
  belongs_to :org_structure
  belongs_to :natural_person, {:foreign_key => "contact"}
  has_many :natural_people, :through => :associates
  validates_associated :org_structure
end

So by my understanding that second "belongs_to" call is supposed to 
enable me to make the assignment that''s failing. It''s 1
o''clock in the
morning, maybe this will make sense after a sleep...




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Michael Henry

2006-Dec-13 14:05 UTC

head link

Assigning objects...

I''m a Ruby Newbie (hey that rhymes!) and I suspect I haven''t
understood
the syntax properly.
I''m trying to assign one ActiveRecord object to the field of another
and
I think this should work:

 >> org = Organisation.new
=> #<Organisation:0xb7652dd8 @new_record=true, 
@attributes={"fax_number"=>nil, "postal_address"=>nil,
"name"=>nil,
"org_structure_id"=>0, "location_address"=>nil,
"tin"=>nil,
"phone_number"=>nil, "contact"=>nil,
"email_address"=>nil}>
 >> org.name = "Aces High Inc."
=> "Aces High Inc."
 >> person = NaturalPerson.new
=> #<NaturalPerson:0xb764997c @new_record=true, 
@attributes={"postal_address"=>nil, "fax_number"=>nil,
"name"=>nil,
"dob"=>nil, "phone_number"=>nil,
"visa"=>nil, "mobile_number"=>nil,
"email_address"=>nil, "nationality"=>nil}>
 >> person.name = "Fred Flinstone"
=> "Fred Flinstone"
 >> org.contact << person
NoMethodError: You have a nil object when you didn''t expect it!
You might have expected an instance of Array.
The error occured while evaluating nil.<<
       from (irb):13

My Organisation model looks like this:

class Organisation < ActiveRecord::Base
 belongs_to :org_structure
 belongs_to :natural_person, {:foreign_key => "contact"}
 has_many :natural_people, :through => :associates
 validates_associated :org_structure
end

So by my understanding that second "belongs_to" call is supposed to 
enable me to make the assignment that''s failing. It''s 1
o''clock in the
morning, maybe this will make sense after a sleep...


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Jason Roelofs

2006-Dec-13 14:25 UTC

head link

Re: Assigning objects...

Well,

"org.contact << person" is the same as saying
"org.contact.<<(person)",
which should make the error message clearer: contact is not defined. I guess
you didn''t quite get what all the ActiveRecord meta-functions do to the
class. The foreign key for :natural_person may be ''contact'',
but that is
purely related to the database.

Sorry, now that I look at the relationships set up, I''m not sure I
follow
what is there. I understand what you are trying to do, but I don''t
think you
know what you''ve got there.

Either way, you will want this if all the associations are correct:

org.natural_people << person

Be sure to spend some more time first with Ruby itself, and then more time
at the Rails docs (api.rubyonrails.com).

Jason

On 12/13/06, Michael Henry
<michael.k.henry-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
>
> I''m a Ruby Newbie (hey that rhymes!) and I suspect I
haven''t understood
> the syntax properly.
> I''m trying to assign one ActiveRecord object to the field of
another and
> I think this should work:
>
> >> org = Organisation.new
> => #<Organisation:0xb7652dd8 @new_record=true,
> @attributes={"fax_number"=>nil,
"postal_address"=>nil, "name"=>nil,
> "org_structure_id"=>0, "location_address"=>nil,
"tin"=>nil,
> "phone_number"=>nil, "contact"=>nil,
"email_address"=>nil}>
> >> org.name = "Aces High Inc."
> => "Aces High Inc."
> >> person = NaturalPerson.new
> => #<NaturalPerson:0xb764997c @new_record=true,
> @attributes={"postal_address"=>nil,
"fax_number"=>nil, "name"=>nil,
> "dob"=>nil, "phone_number"=>nil,
"visa"=>nil, "mobile_number"=>nil,
> "email_address"=>nil, "nationality"=>nil}>
> >> person.name = "Fred Flinstone"
> => "Fred Flinstone"
> >> org.contact << person
> NoMethodError: You have a nil object when you didn''t expect it!
> You might have expected an instance of Array.
> The error occured while evaluating nil.<<
>        from (irb):13
>
> My Organisation model looks like this:
>
> class Organisation < ActiveRecord::Base
> belongs_to :org_structure
> belongs_to :natural_person, {:foreign_key => "contact"}
> has_many :natural_people, :through => :associates
> validates_associated :org_structure
> end
>
> So by my understanding that second "belongs_to" call is supposed
to
> enable me to make the assignment that''s failing. It''s 1
o''clock in the
> morning, maybe this will make sense after a sleep...
>
>
> >
>

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dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Dec-13 14:36 UTC

head link

Re: Assigning objects...

Hi --

On Thu, 14 Dec 2006, Michael Henry wrote:
> I''m a Ruby Newbie (hey that rhymes!)
That''s usually called a "nuby" :-)
> and I suspect I haven''t understood the syntax properly.
> I''m trying to assign one ActiveRecord object to the field of
another and
> I think this should work:
>
> >> org = Organisation.new
> >> org.name = "Aces High Inc."
> >> person = NaturalPerson.new
> >> person.name = "Fred Flinstone"
> >> org.contact << person
> NoMethodError: You have a nil object when you didn''t expect it!
The << is only for collections, where you''re adding one to many
(like
library.books << some_book).  Here there''s only one of
everything.

The method you call on the object, for an association, is always the
name of the association itself.  You have no association called
"contact":
> My Organisation model looks like this:
>
> class Organisation < ActiveRecord::Base
>  belongs_to :org_structure
>  belongs_to :natural_person, {:foreign_key => "contact"}
>  has_many :natural_people, :through => :associates
>  validates_associated :org_structure
> end
Either you need to set the value like this:

   org.natural_person = person

or, if you want to use org.contact, you need to change the
natural_person association to this:

   belongs_to :contact,
              :class_name => "NaturalPerson",
              :foreign_key => "contact_id"

and make any corresponding changes in natural_person.rb


David

-- 
Q. What''s a good holiday present for the serious Rails developer?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
    aka The Ruby book for Rails developers!
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

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Michael Henry

2006-Dec-14 00:59 UTC

head link

Re: Assigning objects...

Thank you Jason and David for your replies!

David said:>>
>>>> org = Organisation.new
>>>> org.name = "Aces High Inc."
>>>> person = NaturalPerson.new
>>>> person.name = "Fred Flinstone"
>>>> org.contact << person
>>>>         
>> NoMethodError: You have a nil object when you didn''t expect
it!
>>     
>
> The << is only for collections, where you''re adding one to
many (like
> library.books << some_book).  Here there''s only one of
everything.
>   
Brilliant! That''s a bit of info that I didn''t have.
> The method you call on the object, for an association, is always the
> name of the association itself.  You have no association called
> "contact":
>
>   
>> My Organisation model looks like this:
>>
>> class Organisation < ActiveRecord::Base
>>  belongs_to :org_structure
>>  belongs_to :natural_person, {:foreign_key => "contact"}
>>  has_many :natural_people, :through => :associates
>>  validates_associated :org_structure
>> end
>>     
OK, this sentence had to make me re-evaluate my understanding of what 
was going on!

I have defined a field "contact" in my table "organisations"
and I was
expecting this statement do set up the association:

    belongs_to :natural_person, :foreign_key => "contact"


In my mind I was saying "Right, it''s going to derive the class
name from
the association, so it will correctly get the NaturalPerson class and 
I''ve stated that the foreign key is called ''contact''
so I can access
that class through the ''contact'' member".

OK, so that is wrong!
> if you want to use org.contact, you need to change the
> natural_person association to this:
>
>    belongs_to :contact,
>               :class_name => "NaturalPerson",
>               :foreign_key => "contact_id"
>
> and make any corresponding changes in natural_person.rb
>   
I do want to use org.contact, so I changed my model as per what you''ve 
put above:

    class Organisation < ActiveRecord::Base
      belongs_to :contact, {:class_name => "NaturalPerson",
:foreign_key
    => "contact"}


The thing that hasn''t clicked in my mind yet is that the association
and
foreign key have the same value - they are redundant (in my particular 
case). So I thought "Maybe the association name is the same as the field 
name by convention, but I could actually use any arbitrary name". So I 
tried this:

    class Organisation < ActiveRecord::Base
      belongs_to :foo, {:class_name => "NaturalPerson",
:foreign_key =>
    "contact"}

So if my presumption is correct, I can update the "contact" field in
the
database by playing with the "foo" association in the ActiveRecord.

     >> org = Organisation.new
     >> org.name = "Wacky Widgets Pty Ltd"
     >> person = NaturalPerson.new
     >> person.name = "Barney Rubble"
     >> org.foo = person
     >> org.save
     >> puts org.foo.name
    Barney Rubble
     >> puts org.contact.name
    NoMethodError: undefined method `name'' for 2:Fixnum
            from (irb):14


By George I think I''ve got it!

"Contact" is just a plain old integer, as I defined it in the 
ActiveRecord::Migration.

If I used "belongs_to" with the association name "contact"
it will
override the integer "contact" and add all the funkiness I''m
looking for.

Thank you, thank you, thank you!






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Rails - Dec 2006 - Assigning objects...

Assigning objects...

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