Rails - Mar 2008 - THE CHALLENGE: How would you do this: has_many :through & polymorphic associations

Hi,

I have a category model and several other models that I want to
categorize.
Categories are organised in a hierarchy.

class Category < ActiveRecord::Base
  acts_as_tree
end

class User < ActiveRecord::Base
end

class Image < ActiveRecord::Base
end

I am quite sure that I am going to have additional models (like User
and Images) that I want to categorize later on.
It should be possible to assign a category to more than one object.
For example I have a category "new" and I want to assign this category
to several user and image records.

So many Images and Users could have many categories and vice versa.

I thought maybe it is possible to implement this with a
has_many :through association in combination with polymorphic => true,
but until now I could not fiqure out how to declare this in the models
and how my migrations have to look like...

Thanks for your help.

Feurio




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I believe you''ll want to add an addition model for the join table that
uses polymorphic associations like this:

class CategorizedItem < ARec::Base
  belongs_to :category
  belongs_to :categorizable, :polymorphic=>true
end

class Category < ARec::Base
  acts_as_tree
  has_many :categoriezed_items
 
has_many :categorizables, :through=>:categorized_items,
:source=>:categorizable
end

class User < ARec::Base
  has_many :categorized_items, :as=>:categorizable # could be has_one
end

class Image < ARec::Base
  has_many :categorized_items, :as=>:categorizable # could be has_one
end

You can use the :source option (as in Categories has_many :through) to
identify which association to use from the join table.

HTH,
AndyV
On Mar 17, 8:26 am, Feurio
<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org>
wrote:
> Hi,
>
> I have a category model and several other models that I want to
> categorize.
> Categories are organised in a hierarchy.
>
> class Category < ActiveRecord::Base
>   acts_as_tree
> end
>
> class User < ActiveRecord::Base
> end
>
> class Image < ActiveRecord::Base
> end
>
> I am quite sure that I am going to have additional models (like User
> and Images) that I want to categorize later on.
> It should be possible to assign a category to more than one object.
> For example I have a category "new" and I want to assign this
category
> to several user and image records.
>
> So many Images and Users could have many categories and vice versa.
>
> I thought maybe it is possible to implement this with a
> has_many :through association in combination with polymorphic => true,
> but until now I could not fiqure out how to declare this in the models
> and how my migrations have to look like...
>
> Thanks for your help.
>
> Feurio
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I created the model like described by you above.

For the CategorizedItem model I used the following migration:

class CreateCategorizedItems < ActiveRecord::Migration
  def self.up
    create_table :categorized_items do |t|
      t.references :categorizable, :null => false, :polymorphic =>
true
      t.timestamps
    end
  end

  def self.down
    drop_table :categorized_items
  end
end

----------
Sadly it seems not to work (completly).
>> c = Category.create
=> #<Category id: 2061879280, name: nil, description: nil, parent_id:
nil, created_at: "2008-03-17 15:16:18", updated_at: "2008-03-17
15:16:18">
>> c.categorizables
ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a
has_many :through association ''Category#categorizables'' on the
polymorphic object ''Categorizable#categorizable''.
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/reflection.rb:187:in `check_validity!''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations/has_many_through_association.rb:6:in
`initialize''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations.rb:1032:in `new''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations.rb:1032:in `categorizables''
        from (irb):4

The following seems to work, but how would I assign a Category to a
Uses?

u = User.create
=> #<User id: 2, created_at: "2008-03-17 15:17:27", updated_at:
"2008-03-17 15:17:27">
>> u.categorized_items
=> []


Thanks,

Feurio

On 17 Mrz., 13:56, AndyV <a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org>
wrote:
> I believe you''ll want to add an addition model for the join table
that
> uses polymorphic associations like this:
>
> class CategorizedItem < ARec::Base
>   belongs_to :category
>   belongs_to :categorizable, :polymorphic=>true
> end
>
> class Category < ARec::Base
>   acts_as_tree
>   has_many :categoriezed_items
>
> has_many :categorizables, :through=>:categorized_items,
:source=>:categorizable
> end
>
> class User < ARec::Base
>   has_many :categorized_items, :as=>:categorizable # could be has_one
> end
>
> class Image < ARec::Base
>   has_many :categorized_items, :as=>:categorizable # could be has_one
> end
>
> You can use the :source option (as in Categories has_many :through) to
> identify which association to use from the join table.
>
> HTH,
> AndyV
> On Mar 17, 8:26 am, Feurio
<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > Hi,
>
> > I have a category model and several other models that I want to
> > categorize.
> > Categories are organised in a hierarchy.
>
> > class Category < ActiveRecord::Base
> >   acts_as_tree
> > end
>
> > class User < ActiveRecord::Base
> > end
>
> > class Image < ActiveRecord::Base
> > end
>
> > I am quite sure that I am going to have additional models (like User
> > and Images) that I want to categorize later on.
> > It should be possible to assign a category to more than one object.
> > For example I have a category "new" and I want to assign
this category
> > to several user and image records.
>
> > So many Images and Users could have many categories and vice versa.
>
> > I thought maybe it is possible to implement this with a
> > has_many :through association in combination with polymorphic =>
true,
> > but until now I could not fiqure out how to declare this in the models
> > and how my migrations have to look like...
>
> > Thanks for your help.
>
> > Feurio
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use the has_many_polymorphs plugin
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You''re missing the ''category'' half of the references:

class CreateCategorizedItems < ActiveRecord::Migration
  def self.up
    create_table :categorized_items do |t|
      t.references :categorizable, :null => false, :polymorphic =>true
      t.references :category, :null => false
      t.timestamps
    end
  end

  def self.down
    drop_table :categorized_items
  end
end




On Mar 17, 10:29 am, Feurio
<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org>
wrote:
> I created the model like described by you above.
>
> For the CategorizedItem model I used the following migration:
>
> class CreateCategorizedItems < ActiveRecord::Migration
>   def self.up
>     create_table :categorized_items do |t|
>       t.references :categorizable, :null => false, :polymorphic =>
> true
>       t.timestamps
>     end
>   end
>
>   def self.down
>     drop_table :categorized_items
>   end
> end
>
> ----------
> Sadly it seems not to work (completly).
>
> >> c = Category.create
>
> => #<Category id: 2061879280, name: nil, description: nil, parent_id:
> nil, created_at: "2008-03-17 15:16:18", updated_at:
"2008-03-17
> 15:16:18">>> c.categorizables
>
> ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a
> has_many :through association ''Category#categorizables''
on the
> polymorphic object ''Categorizable#categorizable''.
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/reflection.rb:187:in `check_validity!''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations/has_many_through_association.rb:6:in
> `initialize''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations.rb:1032:in `new''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations.rb:1032:in `categorizables''
>         from (irb):4
>
> The following seems to work, but how would I assign a Category to a
> Uses?
>
> u = User.create
> => #<User id: 2, created_at: "2008-03-17 15:17:27",
updated_at:
> "2008-03-17 15:17:27">>> u.categorized_items
>
> => []
>
> Thanks,
>
> Feurio
>
> On 17 Mrz., 13:56, AndyV
<a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org> wrote:
>
> > I believe you''ll want to add an addition model for the join
table that
> > uses polymorphic associations like this:
>
> > class CategorizedItem < ARec::Base
> >   belongs_to :category
> >   belongs_to :categorizable, :polymorphic=>true
> > end
>
> > class Category < ARec::Base
> >   acts_as_tree
> >   has_many :categoriezed_items
>
> > has_many :categorizables, :through=>:categorized_items,
:source=>:categorizable
> > end
>
> > class User < ARec::Base
> >   has_many :categorized_items, :as=>:categorizable # could be
has_one
> > end
>
> > class Image < ARec::Base
> >   has_many :categorized_items, :as=>:categorizable # could be
has_one
> > end
>
> > You can use the :source option (as in Categories has_many :through) to
> > identify which association to use from the join table.
>
> > HTH,
> > AndyV
> > On Mar 17, 8:26 am, Feurio
<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > > Hi,
>
> > > I have a category model and several other models that I want to
> > > categorize.
> > > Categories are organised in a hierarchy.
>
> > > class Category < ActiveRecord::Base
> > >   acts_as_tree
> > > end
>
> > > class User < ActiveRecord::Base
> > > end
>
> > > class Image < ActiveRecord::Base
> > > end
>
> > > I am quite sure that I am going to have additional models (like
User
> > > and Images) that I want to categorize later on.
> > > It should be possible to assign a category to more than one
object.
> > > For example I have a category "new" and I want to
assign this category
> > > to several user and image records.
>
> > > So many Images and Users could have many categories and vice
versa.
>
> > > I thought maybe it is possible to implement this with a
> > > has_many :through association in combination with polymorphic
=> true,
> > > but until now I could not fiqure out how to declare this in the
models
> > > and how my migrations have to look like...
>
> > > Thanks for your help.
>
> > > Feurio
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Sorry, still not working...

c = Category.find(943302162)
=> #<Category id: 943302162, name: "computer_science",
description:
"Informatik", parent_id: 2061879279, created_at: "2008-03-18
09:53:21", updated_at: "2008-03-18 09:53:21">

c.categorizables
ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a
has_many :through association ''Category#categorizables'' on the
polymorphic object ''Categorizable#categorizable''.
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/reflection.rb:187:in `check_validity!''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations/has_many_through_association.rb:6:in
`initialize''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations.rb:1032:in `new''
        from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
active_record/associations.rb:1032:in `categorizables''
        from (irb):9


What I have now...

The migration files:
-------------
class CreateCategories < ActiveRecord::Migration
  def self.up
    create_table :categories do |t|
      t.string :name, :description
      t.integer :parent_id
      t.timestamps
    end
  end

  def self.down
    drop_table :categories
  end
end

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|

      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

class CreateCategorizedItems < ActiveRecord::Migration
  def self.up
    create_table :categorized_items do |t|
      t.references :categorizable, :null => false, :polymorphic =>
true
      t.references :category, :null => false
      t.timestamps
    end
  end

  def self.down
    drop_table :categorized_items
  end
end
-------------

The models:
-------------
class Category < ActiveRecord::Base
  acts_as_tree
  has_many :categorized_items
  has_many :categorizables, :through => :categorized_items, :source
=> :categorizable
end

class User < ActiveRecord::Base
  has_many :categorized_items, :as=>:categorizable # could be has_one
end

class CategorizedItem < ActiveRecord::Base
  belongs_to :category
  belongs_to :categorizable, :polymorphic=>true
end

-------------

And how would I do something like the following with the associations
above?

c = Category.create
u = User.create
u.categories << Category


Thanks for your patience!

Feurio

On 17 Mrz., 21:22, AndyV <a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org>
wrote:
> You''re missing the ''category'' half of the
references:
>
> class CreateCategorizedItems < ActiveRecord::Migration
>   def self.up
>     create_table :categorized_items do |t|
>       t.references :categorizable, :null => false, :polymorphic
=>true
>       t.references :category, :null => false
>       t.timestamps
>     end
>   end
>
>   def self.down
>     drop_table :categorized_items
>   end
> end
>
> On Mar 17, 10:29
am,Feurio<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > I created the model like described by you above.
>
> > For the CategorizedItem model I used the following migration:
>
> > class CreateCategorizedItems < ActiveRecord::Migration
> >   def self.up
> >     create_table :categorized_items do |t|
> >       t.references :categorizable, :null => false, :polymorphic
=>
> > true
> >       t.timestamps
> >     end
> >   end
>
> >   def self.down
> >     drop_table :categorized_items
> >   end
> > end
>
> > ----------
> > Sadly it seems not to work (completly).
>
> > >> c = Category.create
>
> > => #<Category id: 2061879280, name: nil, description: nil,
parent_id:
> > nil, created_at: "2008-03-17 15:16:18", updated_at:
"2008-03-17
> > 15:16:18">>> c.categorizables
>
> > ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a
> > has_many :through association
''Category#categorizables'' on the
> > polymorphic object ''Categorizable#categorizable''.
> >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > active_record/reflection.rb:187:in `check_validity!''
> >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > active_record/associations/has_many_through_association.rb:6:in
> > `initialize''
> >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > active_record/associations.rb:1032:in `new''
> >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > active_record/associations.rb:1032:in `categorizables''
> >         from (irb):4
>
> > The following seems to work, but how would I assign a Category to a
> > Uses?
>
> > u = User.create
> > => #<User id: 2, created_at: "2008-03-17 15:17:27",
updated_at:
> > "2008-03-17 15:17:27">>> u.categorized_items
>
> > => []
>
> > Thanks,
>
> >Feurio
>
> > On 17 Mrz., 13:56, AndyV
<a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org> wrote:
>
> > > I believe you''ll want to add an addition model for the
join table that
> > > uses polymorphic associations like this:
>
> > > class CategorizedItem < ARec::Base
> > >   belongs_to :category
> > >   belongs_to :categorizable, :polymorphic=>true
> > > end
>
> > > class Category < ARec::Base
> > >   acts_as_tree
> > >   has_many :categoriezed_items
>
> > > has_many :categorizables, :through=>:categorized_items,
:source=>:categorizable
> > > end
>
> > > class User < ARec::Base
> > >   has_many :categorized_items, :as=>:categorizable # could be
has_one
> > > end
>
> > > class Image < ARec::Base
> > >   has_many :categorized_items, :as=>:categorizable # could be
has_one
> > > end
>
> > > You can use the :source option (as in Categories has_many
:through) to
> > > identify which association to use from the join table.
>
> > > HTH,
> > > AndyV
> > > On Mar 17, 8:26
am,Feurio<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > > > Hi,
>
> > > > I have a category model and several other models that I want
to
> > > > categorize.
> > > > Categories are organised in a hierarchy.
>
> > > > class Category < ActiveRecord::Base
> > > >   acts_as_tree
> > > > end
>
> > > > class User < ActiveRecord::Base
> > > > end
>
> > > > class Image < ActiveRecord::Base
> > > > end
>
> > > > I am quite sure that I am going to have additional models
(like User
> > > > and Images) that I want to categorize later on.
> > > > It should be possible to assign a category to more than one
object.
> > > > For example I have a category "new" and I want to
assign this category
> > > > to several user and image records.
>
> > > > So many Images and Users could have many categories and vice
versa.
>
> > > > I thought maybe it is possible to implement this with a
> > > > has_many :through association in combination with
polymorphic => true,
> > > > but until now I could not fiqure out how to declare this in
the models
> > > > and how my migrations have to look like...
>
> > > > Thanks for your help.
>
> > > >Feurio
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Hi,

thanks everybody for the help.
I got it working now with the plugin has_many_polymorphs.

Would have been nice to get it working with standard rails, too. But
also I was googling and used some reference books like the rails way
or agile webdevelopment with rails I could find a working solution...

Feurio

On 18 Mrz., 10:03, Feurio
<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org>
wrote:
> Sorry, still not working...
>
> c = Category.find(943302162)
> => #<Category id: 943302162, name: "computer_science",
description:
> "Informatik", parent_id: 2061879279, created_at: "2008-03-18
> 09:53:21", updated_at: "2008-03-18 09:53:21">
>
> c.categorizables
> ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a
> has_many :through association ''Category#categorizables''
on the
> polymorphic object ''Categorizable#categorizable''.
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/reflection.rb:187:in `check_validity!''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations/has_many_through_association.rb:6:in
> `initialize''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations.rb:1032:in `new''
>         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> active_record/associations.rb:1032:in `categorizables''
>         from (irb):9
>
> What I have now...
>
> The migration files:
> -------------
> class CreateCategories < ActiveRecord::Migration
>   def self.up
>     create_table :categories do |t|
>       t.string :name, :description
>       t.integer :parent_id
>       t.timestamps
>     end
>   end
>
>   def self.down
>     drop_table :categories
>   end
> end
>
> class CreateUsers < ActiveRecord::Migration
>   def self.up
>     create_table :users do |t|
>
>       t.timestamps
>     end
>   end
>
>   def self.down
>     drop_table :users
>   end
> end
>
> class CreateCategorizedItems < ActiveRecord::Migration
>   def self.up
>     create_table :categorized_items do |t|
>       t.references :categorizable, :null => false, :polymorphic =>
> true
>       t.references :category, :null => false
>       t.timestamps
>     end
>   end
>
>   def self.down
>     drop_table :categorized_items
>   end
> end
> -------------
>
> The models:
> -------------
> class Category < ActiveRecord::Base
>   acts_as_tree
>   has_many :categorized_items
>   has_many :categorizables, :through => :categorized_items, :source
> => :categorizable
> end
>
> class User < ActiveRecord::Base
>   has_many :categorized_items, :as=>:categorizable # could be has_one
> end
>
> class CategorizedItem < ActiveRecord::Base
>   belongs_to :category
>   belongs_to :categorizable, :polymorphic=>true
> end
>
> -------------
>
> And how would I do something like the following with the associations
> above?
>
> c = Category.create
> u = User.create
> u.categories << Category
>
> Thanks for your patience!
>
> Feurio
>
> On 17 Mrz., 21:22, AndyV
<a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org> wrote:
>
> > You''re missing the ''category'' half of the
references:
>
> > class CreateCategorizedItems < ActiveRecord::Migration
> >   def self.up
> >     create_table :categorized_items do |t|
> >       t.references :categorizable, :null => false, :polymorphic
=>true
> >       t.references :category, :null => false
> >       t.timestamps
> >     end
> >   end
>
> >   def self.down
> >     drop_table :categorized_items
> >   end
> > end
>
> > On Mar 17, 10:29
am,Feurio<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > > I created the model like described by you above.
>
> > > For the CategorizedItem model I used the following migration:
>
> > > class CreateCategorizedItems < ActiveRecord::Migration
> > >   def self.up
> > >     create_table :categorized_items do |t|
> > >       t.references :categorizable, :null => false,
:polymorphic =>
> > > true
> > >       t.timestamps
> > >     end
> > >   end
>
> > >   def self.down
> > >     drop_table :categorized_items
> > >   end
> > > end
>
> > > ----------
> > > Sadly it seems not to work (completly).
>
> > > >> c = Category.create
>
> > > => #<Category id: 2061879280, name: nil, description: nil,
parent_id:
> > > nil, created_at: "2008-03-17 15:16:18", updated_at:
"2008-03-17
> > > 15:16:18">>> c.categorizables
>
> > > ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot
have a
> > > has_many :through association
''Category#categorizables'' on the
> > > polymorphic object
''Categorizable#categorizable''.
> > >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > > active_record/reflection.rb:187:in `check_validity!''
> > >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > > active_record/associations/has_many_through_association.rb:6:in
> > > `initialize''
> > >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > > active_record/associations.rb:1032:in `new''
> > >         from /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/
> > > active_record/associations.rb:1032:in `categorizables''
> > >         from (irb):4
>
> > > The following seems to work, but how would I assign a Category to
a
> > > Uses?
>
> > > u = User.create
> > > => #<User id: 2, created_at: "2008-03-17
15:17:27", updated_at:
> > > "2008-03-17 15:17:27">>> u.categorized_items
>
> > > => []
>
> > > Thanks,
>
> > >Feurio
>
> > > On 17 Mrz., 13:56, AndyV
<a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org> wrote:
>
> > > > I believe you''ll want to add an addition model for
the join table that
> > > > uses polymorphic associations like this:
>
> > > > class CategorizedItem < ARec::Base
> > > >   belongs_to :category
> > > >   belongs_to :categorizable, :polymorphic=>true
> > > > end
>
> > > > class Category < ARec::Base
> > > >   acts_as_tree
> > > >   has_many :categoriezed_items
>
> > > > has_many :categorizables, :through=>:categorized_items,
:source=>:categorizable
> > > > end
>
> > > > class User < ARec::Base
> > > >   has_many :categorized_items, :as=>:categorizable #
could be has_one
> > > > end
>
> > > > class Image < ARec::Base
> > > >   has_many :categorized_items, :as=>:categorizable #
could be has_one
> > > > end
>
> > > > You can use the :source option (as in Categories has_many
:through) to
> > > > identify which association to use from the join table.
>
> > > > HTH,
> > > > AndyV
> > > > On Mar 17, 8:26
am,Feurio<govinda.pfis...-enoGyz2oHxeELgA04lAiVw@public.gmane.org> wrote:
>
> > > > > Hi,
>
> > > > > I have a category model and several other models that I
want to
> > > > > categorize.
> > > > > Categories are organised in a hierarchy.
>
> > > > > class Category < ActiveRecord::Base
> > > > >   acts_as_tree
> > > > > end
>
> > > > > class User < ActiveRecord::Base
> > > > > end
>
> > > > > class Image < ActiveRecord::Base
> > > > > end
>
> > > > > I am quite sure that I am going to have additional
models (like User
> > > > > and Images) that I want to categorize later on.
> > > > > It should be possible to assign a category to more than
one object.
> > > > > For example I have a category "new" and I
want to assign this category
> > > > > to several user and image records.
>
> > > > > So many Images and Users could have many categories and
vice versa.
>
> > > > > I thought maybe it is possible to implement this with a
> > > > > has_many :through association in combination with
polymorphic => true,
> > > > > but until now I could not fiqure out how to declare
this in the models
> > > > > and how my migrations have to look like...
>
> > > > > Thanks for your help.
>
> > > > >Feurio
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