Rails - Apr 2009 - Getting the associated model in a join table

Let''s say we have the following models:

Product < ActiveRecord::Base
 has_many :products_suppliers
 has_many :suppliers, :through => :products_supplier

Supplier < ActiveRecord::Base
 has_many :products_suppliers
 has_many :products, :through => :products_supplier

ProductsSupplier < ActiveRecord::Base
 belongs_to :supplier
 belongs_to :product
end


Let'' say we have this data in the products_suppliers table:

| supplier_id |  product_id |
|      1          |       2         |
|      1          |       1         |
|      2          |       2         |
|      2          |       1         |


So when I do this:

@suppliers = Product.find(1).suppliers, it will return an array with the
suppliers with id 1 and 2.

Let''s say I do this:

@supplier = @suppliers[0] #Which is the supplier with id = 1, the one
fetched from the (supplier_id = 1, product_id = 2) record in the
products_suppliers table. Ok, now I got a single instance of a supplier.
**What I want is to get the product_id it was associated with in the
products_suppliers table.** (product_id = 2), might be missing something
simple, but I can''t seem to find a way to do that.

Any help appreciated!

Thanks,

Marcelo.

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Actually the question would be better put this way:

 Having a has_one association via a link table (in this case
products_supplier).

Thanks.

On Mon, Apr 6, 2009 at 3:41 PM, Marcelo de Moraes Serpa
<celoserpa-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> wrote:
> Let''s say we have the following models:
>
> Product < ActiveRecord::Base
>  has_many :products_suppliers
>  has_many :suppliers, :through => :products_supplier
>
> Supplier < ActiveRecord::Base
>  has_many :products_suppliers
>  has_many :products, :through => :products_supplier
>
> ProductsSupplier < ActiveRecord::Base
>  belongs_to :supplier
>  belongs_to :product
> end
>
>
> Let'' say we have this data in the products_suppliers table:
>
> | supplier_id |  product_id |
> |      1          |       2         |
> |      1          |       1         |
> |      2          |       2         |
> |      2          |       1         |
>
>
> So when I do this:
>
> @suppliers = Product.find(1).suppliers, it will return an array with the
> suppliers with id 1 and 2.
>
> Let''s say I do this:
>
> @supplier = @suppliers[0] #Which is the supplier with id = 1, the one
> fetched from the (supplier_id = 1, product_id = 2) record in the
> products_suppliers table. Ok, now I got a single instance of a supplier.
> **What I want is to get the product_id it was associated with in the
> products_suppliers table.** (product_id = 2), might be missing something
> simple, but I can''t seem to find a way to do that.
>
> Any help appreciated!
>
> Thanks,
>
> Marcelo.
>
>
>
>
>
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I couldn''t really get your question, but I think that what you are
trying to do here is to create a many to many relationship.

Rails actually provides the has_and_belongs_to_many association for
this very purpose, which should help you with what you are asking (I
think).

http://guides.rubyonrails.org/association_basics.html#choosing-between-has-many-through-and-has-and-belongs-to-many

On Apr 7, 6:01 am, Marcelo de Moraes Serpa
<celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Actually the question would be better put this way:
>
>  Having a has_one association via a link table (in this case
> products_supplier).
>
> Thanks.
>
> On Mon, Apr 6, 2009 at 3:41 PM, Marcelo de Moraes Serpa
<celose...@gmail.com
>
> > wrote:
> > Let''s say we have the following models:
>
> > Product < ActiveRecord::Base
> >  has_many :products_suppliers
> >  has_many :suppliers, :through => :products_supplier
>
> > Supplier < ActiveRecord::Base
> >  has_many :products_suppliers
> >  has_many :products, :through => :products_supplier
>
> > ProductsSupplier < ActiveRecord::Base
> >  belongs_to :supplier
> >  belongs_to :product
> > end
>
> > Let'' say we have this data in the products_suppliers table:
>
> > | supplier_id |  product_id |
> > |      1          |       2         |
> > |      1          |       1         |
> > |      2          |       2         |
> > |      2          |       1         |
>
> > So when I do this:
>
> > @suppliers = Product.find(1).suppliers, it will return an array with
the
> > suppliers with id 1 and 2.
>
> > Let''s say I do this:
>
> > @supplier = @suppliers[0] #Which is the supplier with id = 1, the one
> > fetched from the (supplier_id = 1, product_id = 2) record in the
> > products_suppliers table. Ok, now I got a single instance of a
supplier.
> > **What I want is to get the product_id it was associated with in the
> > products_suppliers table.** (product_id = 2), might be missing
something
> > simple, but I can''t seem to find a way to do that.
>
> > Any help appreciated!
>
> > Thanks,
>
> > Marcelo.
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Hello Jaryl, thanks for the reply,

habtm is equivalent to has_many :through. just that the join table is not an
entity by itself, this I know :)

So, I will try to explain through an example:

Let''s say we have a products table:

| id | name | price |
|  1 |     a   |  2.50 |
|  2 |     b   |  1.50 |

A suppliers table

| id | name |
|  1 |  s_a  |
|  2 |  s_b  |

So the idea is: A product may be supplied by many different suppliers. So,
indeed, it is a has_and_belongs_to_many relationship. The thing is, the
relationship by itself defines the type of the supplier (if it''s either
a
vendor or a manufacturer), since we have:

products_suppliers table:
| id | supplier_id | product_id | supplier_type |
| 1  |       1         |     1          |   "vendor"      |
| 2  |       1         |      2         | "manufacturer"|

So, in tis case, supplier s_a is a "vendor" of product a and a
"manufacturer" of product b.

Product < ActiveRecord::Base
  has_many :products_suppliers
  has_many :suppliers, :through => :products_suppliers
end

Supplier < ActiveRecord::Base
 has_many :products_suppliers
 has_many :products, :through => :products_suppliers
end

ProductsSupplier < ActiveRecord::Base
 belongs_to :product
 belongs_to :supplier
end


So let''s take this code

p = Product.find(1)


What I need is a specific products_suppliers related to specific combo of
(supplier_id,product_id) keys, so I can get the supplier_type data related
to this product+supplier. However, I the has_many relationship in Supplier
reaturns all the products_suppliers that has supplier_id == the id of this
supplier -- To get the specific products_supplier I would also need the id
of the product that owns this supplier, but I can''t get it. So, the
first
thing I though was something like has_one :through. That''s why I said,
a
has_one relationship through a link table. The thing is, I need the
product_id that owns this supplier from the supplier model. I might as well
just leave AR and do some raw SQL, or maybe use sql :select statemente in
the association to fetch the type from the link table into the association.

Does that make sense?

Thanks,

Marcelo.



On Mon, Apr 6, 2009 at 9:47 PM, Jaryl Sim
<quantum.crusade-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> I couldn''t really get your question, but I think that what you are
> trying to do here is to create a many to many relationship.
>
> Rails actually provides the has_and_belongs_to_many association for
> this very purpose, which should help you with what you are asking (I
> think).
>
>
>
http://guides.rubyonrails.org/association_basics.html#choosing-between-has-many-through-and-has-and-belongs-to-many
>
> On Apr 7, 6:01 am, Marcelo de Moraes Serpa
<celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
> > Actually the question would be better put this way:
> >
> >  Having a has_one association via a link table (in this case
> > products_supplier).
> >
> > Thanks.
> >
> > On Mon, Apr 6, 2009 at 3:41 PM, Marcelo de Moraes Serpa <
> celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> >
> > > wrote:
> > > Let''s say we have the following models:
> >
> > > Product < ActiveRecord::Base
> > >  has_many :products_suppliers
> > >  has_many :suppliers, :through => :products_supplier
> >
> > > Supplier < ActiveRecord::Base
> > >  has_many :products_suppliers
> > >  has_many :products, :through => :products_supplier
> >
> > > ProductsSupplier < ActiveRecord::Base
> > >  belongs_to :supplier
> > >  belongs_to :product
> > > end
> >
> > > Let'' say we have this data in the products_suppliers
table:
> >
> > > | supplier_id |  product_id |
> > > |      1          |       2         |
> > > |      1          |       1         |
> > > |      2          |       2         |
> > > |      2          |       1         |
> >
> > > So when I do this:
> >
> > > @suppliers = Product.find(1).suppliers, it will return an array
with
> the
> > > suppliers with id 1 and 2.
> >
> > > Let''s say I do this:
> >
> > > @supplier = @suppliers[0] #Which is the supplier with id = 1, the
one
> > > fetched from the (supplier_id = 1, product_id = 2) record in the
> > > products_suppliers table. Ok, now I got a single instance of a
> supplier.
> > > **What I want is to get the product_id it was associated with in
the
> > > products_suppliers table.** (product_id = 2), might be missing
> something
> > > simple, but I can''t seem to find a way to do that.
> >
> > > Any help appreciated!
> >
> > > Thanks,
> >
> > > Marcelo.
> >
>
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Hmm, maybe I''m complicating things. Maybe a delegate to the Product
class
(to get the product_id) would solve this... hmm, I will try that and let you
guys know. Well, amazing how the fact of writing to the mailing list helps
to find the solution by yourself :)

Thanks!

Marcelo.

On Tue, Apr 7, 2009 at 12:28 PM, Marcelo de Moraes Serpa <
celoserpa-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hello Jaryl, thanks for the reply,
>
> habtm is equivalent to has_many :through. just that the join table is not
> an entity by itself, this I know :)
>
> So, I will try to explain through an example:
>
> Let''s say we have a products table:
>
> | id | name | price |
> |  1 |     a   |  2.50 |
> |  2 |     b   |  1.50 |
>
> A suppliers table
>
> | id | name |
> |  1 |  s_a  |
> |  2 |  s_b  |
>
> So the idea is: A product may be supplied by many different suppliers. So,
> indeed, it is a has_and_belongs_to_many relationship. The thing is, the
> relationship by itself defines the type of the supplier (if it''s
either a
> vendor or a manufacturer), since we have:
>
> products_suppliers table:
> | id | supplier_id | product_id | supplier_type |
> | 1  |       1         |     1          |   "vendor"      |
> | 2  |       1         |      2         | "manufacturer"|
>
> So, in tis case, supplier s_a is a "vendor" of product a and a
> "manufacturer" of product b.
>
> Product < ActiveRecord::Base
>   has_many :products_suppliers
>   has_many :suppliers, :through => :products_suppliers
> end
>
> Supplier < ActiveRecord::Base
>  has_many :products_suppliers
>  has_many :products, :through => :products_suppliers
> end
>
> ProductsSupplier < ActiveRecord::Base
>  belongs_to :product
>  belongs_to :supplier
> end
>
>
> So let''s take this code
>
> p = Product.find(1)
>
>
> What I need is a specific products_suppliers related to specific combo of
> (supplier_id,product_id) keys, so I can get the supplier_type data related
> to this product+supplier. However, I the has_many relationship in Supplier
> reaturns all the products_suppliers that has supplier_id == the id of this
> supplier -- To get the specific products_supplier I would also need the id
> of the product that owns this supplier, but I can''t get it. So,
the first
> thing I though was something like has_one :through. That''s why I
said, a
> has_one relationship through a link table. The thing is, I need the
> product_id that owns this supplier from the supplier model. I might as well
> just leave AR and do some raw SQL, or maybe use sql :select statemente in
> the association to fetch the type from the link table into the association.
>
> Does that make sense?
>
> Thanks,
>
> Marcelo.
>
>
>
>
> On Mon, Apr 6, 2009 at 9:47 PM, Jaryl Sim
<quantum.crusade-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>wrote:
>
>>
>> I couldn''t really get your question, but I think that what you
are
>> trying to do here is to create a many to many relationship.
>>
>> Rails actually provides the has_and_belongs_to_many association for
>> this very purpose, which should help you with what you are asking (I
>> think).
>>
>>
>>
http://guides.rubyonrails.org/association_basics.html#choosing-between-has-many-through-and-has-and-belongs-to-many
>>
>> On Apr 7, 6:01 am, Marcelo de Moraes Serpa
<celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> wrote:
>> > Actually the question would be better put this way:
>> >
>> >  Having a has_one association via a link table (in this case
>> > products_supplier).
>> >
>> > Thanks.
>> >
>> > On Mon, Apr 6, 2009 at 3:41 PM, Marcelo de Moraes Serpa <
>> celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
>> >
>> > > wrote:
>> > > Let''s say we have the following models:
>> >
>> > > Product < ActiveRecord::Base
>> > >  has_many :products_suppliers
>> > >  has_many :suppliers, :through => :products_supplier
>> >
>> > > Supplier < ActiveRecord::Base
>> > >  has_many :products_suppliers
>> > >  has_many :products, :through => :products_supplier
>> >
>> > > ProductsSupplier < ActiveRecord::Base
>> > >  belongs_to :supplier
>> > >  belongs_to :product
>> > > end
>> >
>> > > Let'' say we have this data in the products_suppliers
table:
>> >
>> > > | supplier_id |  product_id |
>> > > |      1          |       2         |
>> > > |      1          |       1         |
>> > > |      2          |       2         |
>> > > |      2          |       1         |
>> >
>> > > So when I do this:
>> >
>> > > @suppliers = Product.find(1).suppliers, it will return an
array with
>> the
>> > > suppliers with id 1 and 2.
>> >
>> > > Let''s say I do this:
>> >
>> > > @supplier = @suppliers[0] #Which is the supplier with id = 1,
the one
>> > > fetched from the (supplier_id = 1, product_id = 2) record in
the
>> > > products_suppliers table. Ok, now I got a single instance of
a
>> supplier.
>> > > **What I want is to get the product_id it was associated with
in the
>> > > products_suppliers table.** (product_id = 2), might be
missing
>> something
>> > > simple, but I can''t seem to find a way to do that.
>> >
>> > > Any help appreciated!
>> >
>> > > Thanks,
>> >
>> > > Marcelo.
>> >>
>>
>
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On Apr 7, 1:28 pm, Marcelo de Moraes Serpa
<celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> So let''s take this code
>
> p = Product.find(1)
>
> What I need is a specific products_suppliers related to specific combo of
> (supplier_id,product_id) keys, so I can get the supplier_type data related
> to this product+supplier. However, I the has_many relationship in Supplier
> reaturns all the products_suppliers that has supplier_id == the id of this
> supplier -- To get the specific products_supplier I would also need the id
> of the product that owns this supplier, but I can''t get it. So,
the first
> thing I though was something like has_one :through. That''s why I
said, a
> has_one relationship through a link table. The thing is, I need the
> product_id that owns this supplier from the supplier model. I might as well
> just leave AR and do some raw SQL, or maybe use sql :select statemente in
> the association to fetch the type from the link table into the association.
>
> Does that make sense?
>
Maybe this is too obvious, but given the example above, couldn''t you
just use:

p.products_suppliers.find_by_supplier_id(some_supplier_id)

That will give you the supplier that you''re looking for.

BTW, I''d recommend a different name for the supplier_type column -
that pattern (same as the foreign key, with _type instead of _id) is
the Rails convention for single table inheritance, which is NOT what
you''re looking for here. It shouldn''t cause a problem, but the
AR
association code is known to sometimes get really weird indigestion
from that situation...

Hope this helps,

--Matt Jones
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I don''t think a delegate would work. Okay, just to recap on the
database structure:

products
| id | name | price |
|  1 |     a   |  2.50 |
|  2 |     b   |  1.50 |

suppliers
| id | name |
|  1 |  s_a  |
|  2 |  s_b  |

products_suppliers
| id | supplier_id | product_id | supplier_type |
| 1  |       1         |     1          |   "vendor"      |
| 2  |       1         |      2         | "manufacturer"|

Firstly, I don''t think that ''products_suppliers'' is a
good name since
this form is only a requirement for HABTM to work. It should be more
descriptive of the relationship, but your call.

Okay, so I believe that you want to do something like this:

p = Product.first

p.vendors # => [#< Supplier id: 1, name: "s_a">,
#<Supplier id: 2,
name: "s_b">]
p.manufacturer # => #< Supplier id: 1, name: "s_a">

You might want to try this:

class Product < ActiveRecord::Base
  has_many :products_suppliers
  has_many suppliers, :through => products_suppliers

  named_scope :vendors, :conditions => ["supplier_type = ?",
"vendor"]
  named_scope :manufacturer, :conditions => ["supplier_type = ?",
"manufacturer"]
end

This does not restrict the manufacturer to a one-to-many relationship,
so you will have to ensure that each product will have only one
manufacturer (you can do this pretty easily with some validations).

On Apr 8, 11:14 am, Matt Jones
<al2o...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Apr 7, 1:28 pm, Marcelo de Moraes Serpa
<celose...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
>
>
>
>
>
> > So let''s take this code
>
> > p = Product.find(1)
>
> > What I need is a specific products_suppliers related to specific combo
of
> > (supplier_id,product_id) keys, so I can get the supplier_type data
related
> > to this product+supplier. However, I the has_many relationship in
Supplier
> > reaturns all the products_suppliers that has supplier_id == the id of
this
> > supplier -- To get the specific products_supplier I would also need
the id
> > of the product that owns this supplier, but I can''t get it.
So, the first
> > thing I though was something like has_one :through. That''s
why I said, a
> > has_one relationship through a link table. The thing is, I need the
> > product_id that owns this supplier from the supplier model. I might as
well
> > just leave AR and do some raw SQL, or maybe use sql :select statemente
in
> > the association to fetch the type from the link table into the
association.
>
> > Does that make sense?
>
> Maybe this is too obvious, but given the example above, couldn''t
you
> just use:
>
> p.products_suppliers.find_by_supplier_id(some_supplier_id)
>
> That will give you the supplier that you''re looking for.
>
> BTW, I''d recommend a different name for the supplier_type column -
> that pattern (same as the foreign key, with _type instead of _id) is
> the Rails convention for single table inheritance, which is NOT what
> you''re looking for here. It shouldn''t cause a problem,
but the AR
> association code is known to sometimes get really weird indigestion
> from that situation...
>
> Hope this helps,
>
> --Matt Jones
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