Rails - Mar 2009 - Beginner: what to do after adding an association in a model?

I''ve looked at a bunch of tutorials and don''t really
understand what
is supposed to happen after I add an association (belongs_to, has_many
etc) to both sides of a relationship.

A lot of the tutorials just add the associations and move on as if
that''s it, but when I add the association nothing has changed in the
db (which makes sense because at this point I''ve only changed code).
Is there a command I''m supposed to run to look at all the
relationships and add tables/columns for relationships that are
missing them? or am I supposed to manually create the table?

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On Mar 12, 6:05 am, neerolyte
<neerol...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I''ve looked at a bunch of tutorials and don''t really
understand what
> is supposed to happen after I add an association (belongs_to, has_many
> etc) to both sides of a relationship.
>
> A lot of the tutorials just add the associations and move on as if
> that''s it, but when I add the association nothing has changed in
the
> db (which makes sense because at this point I''ve only changed
code).
> Is there a command I''m supposed to run to look at all the
> relationships and add tables/columns for relationships that are
> missing them? or am I supposed to manually create the table?
You''re suppose to use migrations to add columns or create tables (see
http://guides.rubyonrails.org/migrations.html )

Fred
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I dont think so you need to do any thing manually with the db..
Just use the association by using dot operator.
Regards
Rabia

On Thu, Mar 12, 2009 at 11:05 AM, neerolyte
<neerolyte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> I''ve looked at a bunch of tutorials and don''t really
understand what
> is supposed to happen after I add an association (belongs_to, has_many
> etc) to both sides of a relationship.
>
> A lot of the tutorials just add the associations and move on as if
> that''s it, but when I add the association nothing has changed in
the
> db (which makes sense because at this point I''ve only changed
code).
> Is there a command I''m supposed to run to look at all the
> relationships and add tables/columns for relationships that are
> missing them? or am I supposed to manually create the table?
>
> >
>
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Does that mean I have to write a custom migration for it, the only
automated migrations I can find are for adding/removing columns
(AddXXXtoYYY).

Is there something like AddHasAndBelongsToManyModelXToModelY?

Dave.

2009/3/12 Frederick Cheung
<frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> On Mar 12, 6:05 am, neerolyte
<neerol...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> I''ve looked at a bunch of tutorials and don''t really
understand what
>> is supposed to happen after I add an association (belongs_to, has_many
>> etc) to both sides of a relationship.
>>
>> A lot of the tutorials just add the associations and move on as if
>> that''s it, but when I add the association nothing has changed
in the
>> db (which makes sense because at this point I''ve only changed
code).
>> Is there a command I''m supposed to run to look at all the
>> relationships and add tables/columns for relationships that are
>> missing them? or am I supposed to manually create the table?
>
> You''re suppose to use migrations to add columns or create tables
(see
> http://guides.rubyonrails.org/migrations.html )
>
> Fred
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The associations you create in a model have to be backed up by the 
appropriate fields in the DB.

For example:

class Person
  has_many :addresses

class Address
  belongs_to :person

should be a model representation of the relationship inherent in the 
database (the two really go hand-in-hand).

if:

Table people
  id:integer
  first_name:string
  last_name:string

Table address
  id:integer
  person_id:integer
  line1:string
  line2:string
  city:string
  state:string
  postal_code:string

has_many :addresses tells Rails that for a given person, it can use that 
person id field to retrieve address records (those whose person_id 
matches the current person id value). Similarly, from an address, Rails 
can get back to the person record by following the person_id on the 
address.

-- 
Posted via http://www.ruby-forum.com/.

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So building on that example,  you should add a column person_id to the
address table.  Rails will infer the foreign key based on rails model
names.  U can also specify the actual column by passing  :foreign_key
into belongs_to macro.

Roman

On Mar 12, 6:22 am, Ar Chron
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> The associations you create in a model have to be backed up by the
> appropriate fields in the DB.
>
> For example:
>
> class Person
>   has_many :addresses
>
> class Address
>   belongs_to :person
>
> should be a model representation of the relationship inherent in the
> database (the two really go hand-in-hand).
>
> if:
>
> Table people
>   id:integer
>   first_name:string
>   last_name:string
>
> Table address
>   id:integer
>   person_id:integer
>   line1:string
>   line2:string
>   city:string
>   state:string
>   postal_code:string
>
> has_many :addresses tells Rails that for a given person, it can use that
> person id field to retrieve address records (those whose person_id
> matches the current person id value). Similarly, from an address, Rails
> can get back to the person record by following the person_id on the
> address.
>
> --
> Posted viahttp://www.ruby-forum.com/.
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