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Dark Ambient

2006-Sep-24 15:57 UTC

Using :through

Sorry, cause this is the second post in trying to solve the same
problem.  Since that other post hasn''t received any replies and I have
a slightly better understanding I''m trying it again.

In my Position model I have the method company_id
In my Cdetail model I have a method company_id and another company_name.

When I''m pulling up queries on the Position table I want to translate
the company_id in Position to the company_name in Cdetail.

Is this something to use the :through option with or is there another way ?

Stuart

-- 
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Jason Norris

2006-Sep-24 16:46 UTC

head link

Re: Using :through

I assume that Cdetail belongs_to Position?

If so, you could redefine the company_id method

def company_id
    self.Cdetail.company_name
end

Would this work?

Also, if you wanted to use :select in your Find call, you could do

    Position.find(:all, :select =>''[other fields..], 
cdetails.company_name as company_id'', :include =>
''cdetails'')

But now that I''m thinking about it, do you really want to use the field
used for the foreign key to do this? That could cause problems.

Jason

Dark Ambient wrote:> Sorry, cause this is the second post in trying to solve the same
> problem.  Since that other post hasn''t received any replies and I
have
> a slightly better understanding I''m trying it again.
>
> In my Position model I have the method company_id
> In my Cdetail model I have a method company_id and another company_name.
>
> When I''m pulling up queries on the Position table I want to
translate
> the company_id in Position to the company_name in Cdetail.
>
> Is this something to use the :through option with or is there another way ?
>
> Stuart
>
>   

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5MileRadius

2006-Sep-24 16:47 UTC

head link

Re: Using :through

I can''t quite say I followed all of that.  I''d recommend
posting a copy
of the fixture data for both models or a class definition of each model
listing the attributes.



Dark Ambient wrote:> Sorry, cause this is the second post in trying to solve the same
> problem.  Since that other post hasn''t received any replies and I
have
> a slightly better understanding I''m trying it again.
>
> In my Position model I have the method company_id
> In my Cdetail model I have a method company_id and another company_name.
>
> When I''m pulling up queries on the Position table I want to
translate
> the company_id in Position to the company_name in Cdetail.
>
> Is this something to use the :through option with or is there another way ?
> 
> Stuart
> 
> -- 
> http://en.wikipedia.org/wiki/Dark_ambient

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Dark Ambient

2006-Sep-24 17:06 UTC

head link

Re: Using :through

Model: (showing only relevant lines)

class Position < ActiveRecord::Base
belongs_to  :cdetail

attribute: company_id

class Cdetail < ActiveRecord::Base

has_many  :positions

attributes: company_id, company_name

Stuart


On 9/24/06, 5MileRadius
<5mileradius-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> I can''t quite say I followed all of that.  I''d recommend
posting a copy
> of the fixture data for both models or a class definition of each model
> listing the attributes.
>
>
>
> Dark Ambient wrote:
> > Sorry, cause this is the second post in trying to solve the same
> > problem.  Since that other post hasn''t received any replies
and I have
> > a slightly better understanding I''m trying it again.
> >
> > In my Position model I have the method company_id
> > In my Cdetail model I have a method company_id and another
company_name.
> >
> > When I''m pulling up queries on the Position table I want to
translate
> > the company_id in Position to the company_name in Cdetail.
> >
> > Is this something to use the :through option with or is there another
way ?
> >
> > Stuart
> >
> > --
> > http://en.wikipedia.org/wiki/Dark_ambient
>
>
> >
>

-- 
http://en.wikipedia.org/wiki/Dark_ambient

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Dark Ambient

2006-Sep-24 17:10 UTC

head link

Re: Using :through

On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> I assume that Cdetail belongs_to Position?
The other way around , Position belong_to Cdetail
> If so, you could redefine the company_id method
>
> def company_id
>     self.Cdetail.company_name
> end
>
> Would this work?
>
> Also, if you wanted to use :select in your Find call, you could do
>
>     Position.find(:all, :select =>''[other fields..],
> cdetails.company_name as company_id'', :include =>
''cdetails'')
It might work, what is the [other fields] mean ? or can i just exclude
that option ?
> But now that I''m thinking about it, do you really want to use the
field
> used for the foreign key to do this? That could cause problems.
>
> Jason
>I''m not sure , but in looking through my options I thought perhaps I
could use it to define the correct association.

Stuart

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Dark Ambient

2006-Sep-24 17:36 UTC

head link

Re: Using :through

Maybe this will help, because it seems I like my explanations are not
conveying my issue .
I created a sql query in mysql to extract the correct information -
this query works , so now I need to figure out a way for Rails to
perform it.

SELECT
cdetails.company_name
FROM
positions
Inner Join cdetails ON positions.company_id = cdetails.company_id

Hope this helps



Stuart


On 9/24/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> > I assume that Cdetail belongs_to Position?
>
> The other way around , Position belong_to Cdetail
>
> > If so, you could redefine the company_id method
> >
> > def company_id
> >     self.Cdetail.company_name
> > end
> >
> > Would this work?
> >
> > Also, if you wanted to use :select in your Find call, you could do
> >
> >     Position.find(:all, :select =>''[other fields..],
> > cdetails.company_name as company_id'', :include =>
''cdetails'')
>
> It might work, what is the [other fields] mean ? or can i just exclude
> that option ?
>
> > But now that I''m thinking about it, do you really want to use
the field
> > used for the foreign key to do this? That could cause problems.
> >
> > Jason
> >
> I''m not sure , but in looking through my options I thought perhaps
I
> could use it to define the correct association.
>
> Stuart
>

-- 
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Jason Norris

2006-Sep-24 18:02 UTC

head link

Re: Using :through

Like 5MileRadius said, posting your models and possible some controller 
code would help.
But.
To get rails to do that query, you could do

Position.find(:all, :select => ''cdetails.company_name as
whatever'',
:include => ''cdetails'')
that will return an array of Position objects.

When you use :select, the string you pass is what is used in Rails'' 
"SELECT" statement, so only those fields will be queried. If you want 
other things to be retrieved, you must include them in your :select

Jason


Dark Ambient wrote:> Maybe this will help, because it seems I like my explanations are not
> conveying my issue .
> I created a sql query in mysql to extract the correct information -
> this query works , so now I need to figure out a way for Rails to
> perform it.
>
> SELECT
> cdetails.company_name
> FROM
> positions
> Inner Join cdetails ON positions.company_id = cdetails.company_id
>
> Hope this helps
>
>
>
> Stuart
>
>
> On 9/24/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>   
>> On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>     
>>> I assume that Cdetail belongs_to Position?
>>>       
>> The other way around , Position belong_to Cdetail
>>
>>     
>>> If so, you could redefine the company_id method
>>>
>>> def company_id
>>>     self.Cdetail.company_name
>>> end
>>>
>>> Would this work?
>>>
>>> Also, if you wanted to use :select in your Find call, you could do
>>>
>>>     Position.find(:all, :select =>''[other fields..],
>>> cdetails.company_name as company_id'', :include =>
''cdetails'')
>>>       
>> It might work, what is the [other fields] mean ? or can i just exclude
>> that option ?
>>
>>     
>>> But now that I''m thinking about it, do you really want to
use the field
>>> used for the foreign key to do this? That could cause problems.
>>>
>>> Jason
>>>
>>>       
>> I''m not sure , but in looking through my options I thought
perhaps I
>> could use it to define the correct association.
>>
>> Stuart
>>
>>     
>
>
>   

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Dark Ambient

2006-Sep-24 19:38 UTC

head link

Re: Using :through

Could someone explain what posting the models means ? I''m not trying
to be funny, but what I posted was pretty much them. Anyway I''ll post
them here again.

class Position < ActiveRecord::Base
    belongs_to  :state
    belongs_to  :category
    belongs_to  :edureq
    belongs_to  :expreq
    belongs_to  :pay
    belongs_to  :postlength
    belongs_to  :securityclear
    belongs_to  :term
    belongs_to  :travreq
    belongs_to  :wage
    belongs_to  :user
    belongs_to  :cdetail

  def self.current_openings
  find(:all)
  end
end

class Cdetail < ActiveRecord::Base
  belongs_to  :user
  has_many  :positions

end

I thought I could put something into the Position associations like this:

belongs_to:comp_name, :class_name=> "Cdetail", :foreign_key =>
"company_name
and although it wasn''t returning an error it wasn''t giving me
the name.

Stuart

On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:>
> Like 5MileRadius said, posting your models and possible some controller
> code would help.
> But.
> To get rails to do that query, you could do
>
> Position.find(:all, :select => ''cdetails.company_name as
whatever'',
> :include => ''cdetails'')
> that will return an array of Position objects.
>
> When you use :select, the string you pass is what is used in
Rails''
> "SELECT" statement, so only those fields will be queried. If you
want
> other things to be retrieved, you must include them in your :select
>
> Jason
>
>
> Dark Ambient wrote:
> > Maybe this will help, because it seems I like my explanations are not
> > conveying my issue .
> > I created a sql query in mysql to extract the correct information -
> > this query works , so now I need to figure out a way for Rails to
> > perform it.
> >
> > SELECT
> > cdetails.company_name
> > FROM
> > positions
> > Inner Join cdetails ON positions.company_id = cdetails.company_id
> >
> > Hope this helps
> >
> >
> >
> > Stuart
> >
> >
> > On 9/24/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> >> On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >>
> >>> I assume that Cdetail belongs_to Position?
> >>>
> >> The other way around , Position belong_to Cdetail
> >>
> >>
> >>> If so, you could redefine the company_id method
> >>>
> >>> def company_id
> >>>     self.Cdetail.company_name
> >>> end
> >>>
> >>> Would this work?
> >>>
> >>> Also, if you wanted to use :select in your Find call, you
could do
> >>>
> >>>     Position.find(:all, :select =>''[other
fields..],
> >>> cdetails.company_name as company_id'', :include =>
''cdetails'')
> >>>
> >> It might work, what is the [other fields] mean ? or can i just
exclude
> >> that option ?
> >>
> >>
> >>> But now that I''m thinking about it, do you really
want to use the field
> >>> used for the foreign key to do this? That could cause
problems.
> >>>
> >>> Jason
> >>>
> >>>
> >> I''m not sure , but in looking through my options I
thought perhaps I
> >> could use it to define the correct association.
> >>
> >> Stuart
> >>
> >>
> >
> >
> >
>
>
> >
>

-- 
http://en.wikipedia.org/wiki/Dark_ambient

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Dark Ambient

2006-Sep-24 22:59 UTC

head link

Re: Using :through

This is one messy thread.  Anyway , I worked out this problem using
find_by_sql.  Why I can''t do it through the AR associations is beyond
me. I don''t know if I feel right using find_by_sql, as it
doesn''t
really take advantage of the associations that are in place.  Does it
have a downside ?   I''ve posted my models as requested below anyway.

Stuart

On 9/24/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> Could someone explain what posting the models means ? I''m not
trying
> to be funny, but what I posted was pretty much them. Anyway I''ll
post
> them here again.
>
> class Position < ActiveRecord::Base
>     belongs_to  :state
>     belongs_to  :category
>     belongs_to  :edureq
>     belongs_to  :expreq
>     belongs_to  :pay
>     belongs_to  :postlength
>     belongs_to  :securityclear
>     belongs_to  :term
>     belongs_to  :travreq
>     belongs_to  :wage
>     belongs_to  :user
>     belongs_to  :cdetail
>
>   def self.current_openings
>   find(:all)
>   end
> end
>
> class Cdetail < ActiveRecord::Base
>   belongs_to  :user
>   has_many  :positions
>
> end
>
> I thought I could put something into the Position associations like this:
>
> belongs_to:comp_name, :class_name=> "Cdetail", :foreign_key
=> "company_name
> and although it wasn''t returning an error it wasn''t
giving me the name.
>
> Stuart
>
> On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> > Like 5MileRadius said, posting your models and possible some
controller
> > code would help.
> > But.
> > To get rails to do that query, you could do
> >
> > Position.find(:all, :select => ''cdetails.company_name as
whatever'',
> > :include => ''cdetails'')
> > that will return an array of Position objects.
> >
> > When you use :select, the string you pass is what is used in
Rails''
> > "SELECT" statement, so only those fields will be queried. If
you want
> > other things to be retrieved, you must include them in your :select
> >
> > Jason
> >
> >
> > Dark Ambient wrote:
> > > Maybe this will help, because it seems I like my explanations are
not
> > > conveying my issue .
> > > I created a sql query in mysql to extract the correct information
-
> > > this query works , so now I need to figure out a way for Rails to
> > > perform it.
> > >
> > > SELECT
> > > cdetails.company_name
> > > FROM
> > > positions
> > > Inner Join cdetails ON positions.company_id = cdetails.company_id
> > >
> > > Hope this helps
> > >
> > >
> > >
> > > Stuart
> > >
> > >
> > > On 9/24/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > >
> > >> On 9/24/06, Jason Norris
<jasonmnorris-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > >>
> > >>> I assume that Cdetail belongs_to Position?
> > >>>
> > >> The other way around , Position belong_to Cdetail
> > >>
> > >>
> > >>> If so, you could redefine the company_id method
> > >>>
> > >>> def company_id
> > >>>     self.Cdetail.company_name
> > >>> end
> > >>>
> > >>> Would this work?
> > >>>
> > >>> Also, if you wanted to use :select in your Find call, you
could do
> > >>>
> > >>>     Position.find(:all, :select =>''[other
fields..],
> > >>> cdetails.company_name as company_id'', :include
=> ''cdetails'')
> > >>>
> > >> It might work, what is the [other fields] mean ? or can i
just exclude
> > >> that option ?
> > >>
> > >>
> > >>> But now that I''m thinking about it, do you
really want to use the field
> > >>> used for the foreign key to do this? That could cause
problems.
> > >>>
> > >>> Jason
> > >>>
> > >>>
> > >> I''m not sure , but in looking through my options I
thought perhaps I
> > >> could use it to define the correct association.
> > >>
> > >> Stuart
> > >>
> > >>
> > >
> > >
> > >
> >
> >
> > > >
> >
>
>
> --
> http://en.wikipedia.org/wiki/Dark_ambient
>

-- 
http://en.wikipedia.org/wiki/Dark_ambient

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ASE

2006-Sep-25 13:05 UTC

head link

Re: Using :through

Stuart Fellowes wrote:> class Position < ActiveRecord::Base
>     belongs_to  :cdetail
>     belongs_to :user
> end
> class Cdetail < ActiveRecord::Base
>   has_many  :positions
> end
I think your original question was, how do I get the the cdetails''s 
company_name, given a position. Why can''t you just do:

position.cdetail.company_name

?

"belongs_to :cdetail" adds an accessor method to Position which
results
in the Cdetail referenced by the cdetail_id field in Position (you can 
change the name of the field with :foreign_key, if your field is named 
something other than cdetail_id).

There''s no reason to use :through here. :through is used to connect two
tables with another table between them (as an alternative to habtm). You 
might want to say

class Cdetail < ActiveRecord::Base
  has_many :positions
  has_many :users, :through => :positions
end

if you wanted to access users directly from cdetail (use :foreign_key 
and :source if the field names are weird).

When people were asking for your models, maybe they really wanted your 
schema, so they could see what your field names were called to decide if 
you needed foreign_keys, etc.

Tangent: Is there a reason you''re using an unintuitive reference like 
"cdetail"? Why not just call it a "company", with fields
"id" and
"name"? Or even "company_detail"?

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

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Dark Ambient

2006-Sep-25 14:02 UTC

head link

Re: Using :through

On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
> I think your original question was, how do I get the the
cdetails''s
> company_name, given a position. Why can''t you just do:
>
> position.cdetail.company_name
>
> ?
No, that is just giving me "undefined method `cdetail'' for
#<Position:0x4c56748>"

> "belongs_to :cdetail" adds an accessor method to Position which
results
> in the Cdetail referenced by the cdetail_id field in Position (you can
> change the name of the field with :foreign_key, if your field is named
> something other than cdetail_id).
Well , I''ve been trying this and it seems to have no effect -
continuing to get undefined method - "cdetail"

Here is the relationship defined in Position model
belongs_to  :cdetail, :foreign_key => :company_id

So, in the Position model , the attribute is company_id
and in the Cdetail model, the attribute is company_id , perhaps having
both columns with the same name is confusing the issue.
> if you wanted to access users directly from cdetail (use :foreign_key
> and :source if the field names are weird).
I haven''t gotten a good feel for the :source option.  Reading through
the doc it seems to reference another model ?
> Tangent: Is there a reason you''re using an unintuitive reference
like
> "cdetail"? Why not just call it a "company", with
fields "id" and
> "name"? Or even "company_detail"?
>Because I didn''t think it through and I''m being hard headed :)
Actually company_detail maybe a better idea, if that would truly help
the association problem.  The c in cdetail obviously stands for
company.  Just in case it seemed my model naming is totally
irrelevant.

For the time being I solved the issue by adding the :join option to
the find.  It''s not totally ugly and seems to give me the results.
However I''d like to do it, as said above
position.cdetail.company_name.

Stuart


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dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org

2006-Sep-25 14:13 UTC

head link

Re: Using :through

Hi --

On Mon, 25 Sep 2006, Dark Ambient wrote:
>
> On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>
>> I think your original question was, how do I get the the
cdetails''s
>> company_name, given a position. Why can''t you just do:
>>
>> position.cdetail.company_name
>>
>> ?
>
> No, that is just giving me "undefined method `cdetail'' for
> #<Position:0x4c56748>"
>
>
>> "belongs_to :cdetail" adds an accessor method to Position
which results
>> in the Cdetail referenced by the cdetail_id field in Position (you can
>> change the name of the field with :foreign_key, if your field is named
>> something other than cdetail_id).
>
> Well , I''ve been trying this and it seems to have no effect -
> continuing to get undefined method - "cdetail"
>
> Here is the relationship defined in Position model
> belongs_to  :cdetail, :foreign_key => :company_id
>
> So, in the Position model , the attribute is company_id
> and in the Cdetail model, the attribute is company_id , perhaps having
> both columns with the same name is confusing the issue.
>
>> if you wanted to access users directly from cdetail (use :foreign_key
>> and :source if the field names are weird).
>
> I haven''t gotten a good feel for the :source option.  Reading
through
> the doc it seems to reference another model ?
>
>> Tangent: Is there a reason you''re using an unintuitive
reference like
>> "cdetail"? Why not just call it a "company", with
fields "id" and
>> "name"? Or even "company_detail"?
>>
> Because I didn''t think it through and I''m being hard
headed :)
> Actually company_detail maybe a better idea, if that would truly help
> the association problem.  The c in cdetail obviously stands for
> company.  Just in case it seemed my model naming is totally
> irrelevant.
>
> For the time being I solved the issue by adding the :join option to
> the find.  It''s not totally ugly and seems to give me the results.
> However I''d like to do it, as said above
> position.cdetail.company_name.
It seems a little over-engineered, perhaps.  Since you have a
companies table, why not just put the details of the companies in that
table?  Then each position could have a company, which in turn would
have a name:

   position.company.name


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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ASE

2006-Sep-25 15:17 UTC

head link

Re: Using :through

Stuart Fellowes wrote:> So, in the Position model , the attribute is company_id
> and in the Cdetail model, the attribute is company_id , perhaps having
> both columns with the same name is confusing the issue.
Is company_id the primary key attribute for cdetail? That could be the 
problem, since Rails assumes the primary key attribute will be id. If 
you''re using a weird primary key, make sure you use
ActiveRecord::Base''s
primary_key method in the model to tell Rails about it. Having a weird 
primary key might cause belongs_to to fail and not add the cdetail 
method to Position. I''d seriously recommend your primary key just be 
''id''. If I''m not just misunderstanding you.

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ASE

2006-Sep-25 15:26 UTC

head link

Re: Using :through

David wrote:> It seems a little over-engineered, perhaps.  Since you have a
> companies table, why not just put the details of the companies in that
> table?  Then each position could have a company, which in turn would
> have a name:
Stuart, just to clarify: Do you have a companies table, which Position 
and Cdetail reference with their company_id field? Or is 
Position.company_id referencing a Cdetail record identified by it''s 
company_id field? Or is company_id not a record id at all, and some 
other id (like, from another database)?

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Dark Ambient

2006-Sep-25 16:14 UTC

head link

Re: Using :through

On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> David wrote:
> > It seems a little over-engineered, perhaps.  Since you have a
> > companies table, why not just put the details of the companies in that
> > table?  Then each position could have a company, which in turn would
> > have a name:
>
> Stuart, just to clarify: Do you have a companies table, which Position
> and Cdetail reference with their company_id field? Or is
> Position.company_id referencing a Cdetail record identified by
it''s
> company_id field? Or is company_id not a record id at all, and some
> other id (like, from another database)?
>
> --
So many choices :) ..  It is Position.company_id is referencing a
Cdetail record with a company_id field.  For sanity sake here are the
tables:

cdetails

|   id  |   company_id  |  company_name |  other fields for company information
+-----+----------------------+-------------------------+-----------------------------------------------------

positions
| id |   company_id     | other fields for position information
+---+------------------------+--------------------------------------------------

You should see from above that (unfortunately cdetails id is not the
actual company id.  Maybe it would make sense to have that though,
eliminate the company_id and make the id non incremental and place the
company_id there ?
That would probably make it available for reference as
position.cdetail.company_name.

What''s happening here and possibly was born out of adding to the
schema as I move along -
users do a "light" registration first - which is a login name and
password, afterwards to move up in the site''s food chain for
permissions they fill out a details profile.

Stuart

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ASE

2006-Sep-25 16:23 UTC

head link

Re: Using :through

Stuart Fellowes wrote:> I haven''t gotten a good feel for the :source option.  Reading
through
> the doc it seems to reference another model ?
It describes how to get at the other model in a many-to-many 
relationship with weird fieldnames.

For a many-to-many "has_many :through" relationship, Rails assumes you
have a schema like the following (habtm wouldn''t have a Second.id):

First:
  id
Second:
  id
  first_id
  third_id
Third
  id

and models like

class First < ActiveRecord::Base
  has_many :thirds, :through => :seconds
end
class Second < ActiveRecord::Base
  belongs_to :first
  belongs_to :third
end
class Third < ActiveRecord::Base
  has_many :firsts, :through => :seconds
end

This sets up a many-to-many relationship between First and Third. Now if 
your Second schema was like this:

Second:
  id
  weird_first_id
  weird_third_id

...then Rails''s assumption about what your fields will be called will
be
wrong and you have to tell it, like this:

class First < ActiveRecord::Base
  has_many :thirds, :through => :seconds,
    :foreign_key => :weird_first_id, :source => :weird_third_id
end
class Second < ActiveRecord::Base
  belongs_to :first, :foreign_key => :weird_first_id
  belongs_to :third, :foreign_key => :weird_third_id
end
class Third < ActiveRecord::Base
  has_many :firsts, :through => :seconds,
    :foreign_key => :weird_third_id, :source => weird_first_id
end

I hope I got that all right.

has_many tell Rails that (or actually, tells Rails to set up accessor 
methods based on the assumption that) there is another table out there 
which references this model and has field which stores the id of a 
record in this model. So has_many''s :foreign_key is talking about the 
field in the other table.

belongs_to tells Rails that this model references a record in another 
table, and that this model stores the id of a record in the other table. 
So belongs_to''s :foreign_key is talking about the field in this table.

has_many :through tell Rails that this table is joined to another (far) 
table by a middle table which has fields which store the ids of a record 
in this table and a record in the far table. So has_many :through''s 
:foreign_key talks about a field in the middle table referencing this 
table, and has_many :through''s :source talks about a field in the
middle
table referencing the far table.

:source is ONLY used for :through associations, so it doesn''t apply to 
your Cdetail/Person relationship (which is one-to-many, not 
many-to-many, which is what :through is primarily for).

Just saw your last post, will follow up.

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ASE

2006-Sep-25 17:02 UTC

head link

Re: Using :through

If company_id holds a value you''re getting from somewhere else, then 
don''t make it your primary key.

The problem is that you have two "unique" ids for a cdetail, a record
id
and a company id. Rails uses record ids to build relationship accessor 
methods, but you have a valid reason to want to use the company id in 
creating positions, I''m guessing, that the user who creates new 
positions knows and can input the company id to which the position 
should belong, but not its record id in the database (and why should 
they?)

To keep your database normalized, I would remove the company_id field 
from Position and replace it with a cdetail_id, so you can use all of 
Rails'' relationship goodness. Then override Position''s
initialize method
to get the correct cdetail_id from a company_id:

if cdetail_id.nil? and company_id
  cdetail = Cdetail.find_by_company_id company_id
  cdetail_id = cdetail.id unless cdetail.nil?
end

Then when you save, the position will refer to the correct Cdetail 
record (the save will ignore the company_id property in the Position if 
there''s no corresponding field in the table). Maybe add a validation
for
cdetail_id which complains about company_id?

Then when you need the company_id (or, silimlarly, company_name) for a 
position, you do:

position.cdetail.company_id

I would also recommend that you rename company_id to something that 
doesn''t have such associations for other Rails coders, like 
company_identifier. Another rails coder who saw a field named company_id 
would assume you have a table named companies and might get confused.

Again, for clarity, where does the content for the company_id field come 
from? If it''s entirely internal, I would get rid of it and just use the
cdetails'' id field as the unique identifier and present the user with a
menu of company names (or something).

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Dark Ambient

2006-Sep-25 17:46 UTC

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Re: Using :through

On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> If company_id holds a value you''re getting from somewhere else,
then
> don''t make it your primary key.
>
> The problem is that you have two "unique" ids for a cdetail, a
record id
> and a company id. Rails uses record ids to build relationship accessor
> methods, but you have a valid reason to want to use the company id in
> creating positions, I''m guessing, that the user who creates new
> positions knows and can input the company id to which the position
> should belong, but not its record id in the database (and why should
> they?)
Actually without sounding too screwey, I''m grabbing it out of the
session information.
> To keep your database normalized, I would remove the company_id field
> from Position and replace it with a cdetail_id, so you can use all of
> Rails'' relationship goodness. Then override Position''s
initialize method
> to get the correct cdetail_id from a company_id:
>
> if cdetail_id.nil? and company_id
>   cdetail = Cdetail.find_by_company_id company_id
>   cdetail_id = cdetail.id unless cdetail.nil?
> end
I''m thinking all this wouldn''t be necessary. All I''m
really doing is
taking the user_id out of the session information and calling that the
company_id.  Renaming the position.company_id to cdetail_id shouldn''t
effect the creation of the position.  btw, if it means anything, I''m
using a hidden field to input this id.  You did say the magic words
though "normalize the database". Yes that is important.
> Then when you save, the position will refer to the correct Cdetail
> record (the save will ignore the company_id property in the Position if
> there''s no corresponding field in the table). Maybe add a
validation for
> cdetail_id which complains about company_id?
>
> Then when you need the company_id (or, silimlarly, company_name) for a
> position, you do:
>
> position.cdetail.company_id
K. that makes sense. I''ll be trying it shortly and let you know how it
works out.

> Again, for clarity, where does the content for the company_id field come
> from? If it''s entirely internal, I would get rid of it and just
use the
> cdetails'' id field as the unique identifier and present the user
with a
> menu of company names (or something).
>
Again, company_id in both the positions table and the cdetails table
comes from the user id in the session information.

Stuart

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ASE

2006-Sep-25 18:22 UTC

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Re: Using :through

Stuart Fellowes wrote:> Again, company_id in both the positions table and the cdetails table
> comes from the user id in the session information.
Wow, okay.

So if I understand you, each user can have one cdetail and many 
positions.

Forget what I said before. I would set up a has_one/belongs_to 
relationship between User and Cdetail, and a has_many/belongs_to 
relationship between User and Position. That''s it. Then to get the 
Cdetail from a Position, I would do this:

position.user.cdetail

And seriously, I would rename cdetails to companies, and company_id to 
user_id. It''s a lot easier to read and maintain if the methods and 
properties describe what they''re referring to.

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Dark Ambient

2006-Sep-25 18:52 UTC

head link

Re: Using :through

On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Stuart Fellowes wrote:
> > Again, company_id in both the positions table and the cdetails table
> > comes from the user id in the session information.
>
> Wow, okay.
>
> So if I understand you, each user can have one cdetail and many
> positions.
>
> Forget what I said before. I would set up a has_one/belongs_to
> relationship between User and Cdetail, and a has_many/belongs_to
> relationship between User and Position. That''s it. Then to get the
> Cdetail from a Position, I would do this:
>
> position.user.cdetail
>
> And seriously, I would rename cdetails to companies, and company_id to
> user_id. It''s a lot easier to read and maintain if the methods and
> properties describe what they''re referring to.
>
> --
Got to run out , but will work on this in a few hours.
  Let you know how things work out a little later.

Stuart

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Dark Ambient

2006-Sep-25 21:38 UTC

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Re: Using :through

On 9/25/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:

Followed through a was returned
You have a nil object when you didn''t expect it!
The error occurred while evaluating nil.cdetail>
> Forget what I said before. I would set up a has_one/belongs_to
> relationship between User and Cdetail, and a has_many/belongs_to
> relationship between User and Position. That''s it. Then to get the
> Cdetail from a Position, I would do this:
>
> position.user.cdetail
So here is the models just to show that i followed above correctly:
Actually all these relationships existed already.

class User < ActiveRecord::Base
  has_one :cdetail
  has_many  :positions
  before_create :make_activation_code

class Position < ActiveRecord::Base

    belongs_to  :user
    belongs_to  :cdetail

class Cdetail < ActiveRecord::Base
  belongs_to  :user
  has_many  :positions

Maybe I''m doing something wrong here .

stuart

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ASE

2006-Sep-26 12:16 UTC

head link

Re: Using :through

Just do (in shorthand):

class User; has_one :cdetail; has_many :positions; end
class Cdetail; belongs_to :user; end
class Position; belongs_to :user; end

User is the common connection between Position and Cdetail, but it is 
not a join table (C and P point to U, not the other way around), so you 
can''t do habtm or hmt. Make sure the fields which hold the referenced 
ids are named properly or you tell Rails what they''re named in the 
relationship definition (user_id, or :foreign_key => :company_id).

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Dark Ambient

2006-Sep-26 12:34 UTC

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Re: Using :through

On 9/26/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Just do (in shorthand):
>
> class User; has_one :cdetail; has_many :positions; end
> class Cdetail; belongs_to :user; end
> class Position; belongs_to :user; end
>
> User is the common connection between Position and Cdetail, but it is
> not a join table (C and P point to U, not the other way around), so you
> can''t do habtm or hmt. Make sure the fields which hold the
referenced
> ids are named properly or you tell Rails what they''re named in the
> relationship definition (user_id, or :foreign_key => :company_id).
>
I''m not sure I understand why I need to go through User to get what I
need out of Cdetail.  Anyway, before explaining , let me try and
understand it first on my own.
However, as suggested I''ve made some changes, renaming Cdetail to
Company

Company has these relevant attributes:
id : auto_incrementing
company_id
name

Position has this relevant attribute:
company_id

So what I thought made sense here was to add association like this to Position
belongs_to: company, :foreign_key => company_id

Then in show, list
position.company.name

Maybe it makes sense to go through User but truthfully it''s not giving
me any better results.

Stuart

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Ashley Thomas

2006-Sep-26 18:02 UTC

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Re: Using :through

Stuart Fellowes wrote:> Again, company_id in both the positions table and the cdetails table
> comes from the user id in the session information.
Stuart Fellowes wrote:> Company
> company_id
> 
> Position
> company_id
> 
> So what I thought made sense here was to add association like this to 
> Position
> belongs_to: company, :foreign_key => company_id
I think your own naming conventions are confusing you (they''re
confusing
me). As you said before, company_id holds the id of a record in the 
users table (so please, please rename it user_id -- you''ll be thankful 
you did in three months). When you say "Position belongs_to :company, : 
foreign_key => :company_id", you''re telling Rails that
company_id holds
an id of a record in the companies table, which is not the case.

Position and Company both "point to" User, in that they each have a 
field which holds the id of a record in users. They have no relationship 
with each other except indirectly through User (but not in a habtm or 
hmt way). Once you''ve set up the basic relationships from C->U and
P->U,
you can write a simple method in Position like this:

def company
  user.company
end

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Dark Ambient

2006-Sep-26 18:09 UTC

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Re: Using :through

bump :)

Stuart

On 9/26/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 9/26/06, ASE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
> >
> > Just do (in shorthand):
> >
> > class User; has_one :cdetail; has_many :positions; end
> > class Cdetail; belongs_to :user; end
> > class Position; belongs_to :user; end
> >
> > User is the common connection between Position and Cdetail, but it is
> > not a join table (C and P point to U, not the other way around), so
you
> > can''t do habtm or hmt. Make sure the fields which hold the
referenced
> > ids are named properly or you tell Rails what they''re named
in the
> > relationship definition (user_id, or :foreign_key => :company_id).
> >
>
> I''m not sure I understand why I need to go through User to get
what I
> need out of Cdetail.  Anyway, before explaining , let me try and
> understand it first on my own.
> However, as suggested I''ve made some changes, renaming Cdetail to
Company
>
> Company has these relevant attributes:
> id : auto_incrementing
> company_id
> name
>
> Position has this relevant attribute:
> company_id
>
> So what I thought made sense here was to add association like this to
Position
> belongs_to: company, :foreign_key => company_id
>
> Then in show, list
> position.company.name
>
> Maybe it makes sense to go through User but truthfully it''s not
giving
> me any better results.
>
> Stuart
>

-- 
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Dark Ambient

2006-Sep-26 18:22 UTC

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Re: Using :through

On 9/26/06, Ashley Thomas
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Stuart Fellowes wrote:
> > Again, company_id in both the positions table and the cdetails table
> > comes from the user id in the session information.
>
> Stuart Fellowes wrote:
> > Company
> > company_id
> >
> > Position
> > company_id
> >
> > So what I thought made sense here was to add association like this to
> > Position
> > belongs_to: company, :foreign_key => company_id
>
> I think your own naming conventions are confusing you (they''re
confusing
> me). As you said before, company_id holds the id of a record in the
> users table (so please, please rename it user_id -- you''ll be
thankful
> you did in three months). When you say "Position belongs_to :company,
:
> foreign_key => :company_id", you''re telling Rails that
company_id holds
> an id of a record in the companies table, which is not the case.
company_id DOES hold a record in the companies table.
companies:
|  id  |  company_id  | company_name | address | city | so on ............

So why can I just connect these two tables , even though I realize the
id in the companies table is not the standard id as far as AR goes ?
Am I crazy and beating a dead horse or can this not be done.  I am
under the impression there are ways to let AR know of these unusual
attribute names ?

Stuart

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Dark Ambient

2006-Sep-26 19:06 UTC

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Re: Using :through

On 9/26/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 9/26/06, Ashley Thomas
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
I know by now ya think I''m crazy but I put it together exactly how
recommended.  I''m still getting an undefined method for company.

class Company < ActiveRecord::Base
  belongs_to  :user
end

class User < ActiveRecord::Base
  has_one :company
end

class Position < ActiveRecord::Base
...........
   belongs_to  :user
end

companies table:
|  id    | user_id   |   name   |

users table:

| id   |  company_id |    # I also tried changing this to user_id
(rebooted server) no dice

I added this to the position.rb controller:
 def company
 user.company
 end

Calling it through:
position.company.name %>

Stuart

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Dark Ambient

2006-Sep-26 23:17 UTC

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Re: Using :through

Since I tried everything suggested, read and googled with no end in
site - I came up with what I think is a viable solution, I made the
company id attribute not to auto increment but to use the company id
in that column.  Seems to work , any possible problems ?

Stuart

On 9/26/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> On 9/26/06, Dark Ambient
<sambient-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > On 9/26/06, Ashley Thomas
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>
> I know by now ya think I''m crazy but I put it together exactly how
> recommended.  I''m still getting an undefined method for company.
>
> class Company < ActiveRecord::Base
>   belongs_to  :user
> end
>
> class User < ActiveRecord::Base
>   has_one :company
> end
>
> class Position < ActiveRecord::Base
> ...........
>    belongs_to  :user
> end
>
> companies table:
> |  id    | user_id   |   name   |
>
> users table:
>
> | id   |  company_id |    # I also tried changing this to user_id
> (rebooted server) no dice
>
> I added this to the position.rb controller:
>  def company
>  user.company
>  end
>
> Calling it through:
> position.company.name %>
>
> Stuart
>

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Rails - Sep 2006 - Using :through

Using :through

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