Help With has_many and belongs_to :through assocaitions

Hi all, I am having problems with some reasonably complex assocaitions involving has_many and belongs_to with the :through option.

I have three models:

class Site < ActiveRecord::Base   has_many :site_page_relationships   has_many :pages, :through => :pagesite_page_relationships_relationships, :source => :child_page end

class PageRelationship < ActiveRecord::Base   belongs_to :site   belongs_to :parent_page, :foreign_key => :parent_page_id,         :class_name => :page   belongs_to :child_page, :foreign_key => :child_page_id,         :class_name => :page end

class Page < ActiveRecord::Base   has_many :page_relationships, :foreign_key => :child_page_id   has_many :child_pages, :through => :page_relationships,         :source => :child_page   has_many :parent_pages, :through => :page_relationships,         :source => :parent_page end

The idea being that you can have multipe sites each with their own sitetree, and the ability to share pages between sites but in different positions in the site tree.

When I try the following in 'script/console':

page1 = Page.new

=> #<Page:0x279bb60 @attributes={}, @new_record=true>

page1.save

=> true

page2 = Page.new

=> #<Page:0x27944b4 @attributes={}, @new_record=true>

page2.save

=> true

site = Site.new

=> #<Site:0x278e208 @attributes={"name"=>nil, "updated_at"=>nil, "url"=>nil, "description"=>nil, "created_at"=>nil}, @new_record=true>

site.save

=> true

rel1 = PageRelationship.new(:parent_page => page1, :child_page => page2, :site => site)

TypeError: can't convert Symbol into String         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:1003:in `type_name_with_module'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:1242:in `compute_type'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/reflection.rb:112:in `klass'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/association_proxy.rb:133:in `raise_on_type_mismatch'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations/belongs_to_association.rb:22:in `replace'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations.rb:850:in `child_page='         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:1510:in `attributes='         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:1509:in `attributes='         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/base.rb:1354:in `initialize_without_callbacks'         from /usr/local/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/callbacks.rb:236:in `initialize'         from (irb):11

You can see that I get this error? It's really bugging me, I can't figure out why. Any suggestions/ideas would be much appreciated.

Many Thanks

Mark Dodwell

class Site < ActiveRecord::Base has_many :site_page_relationships has_many :pages, :through =>

:pagesite_page_relationships_relationships, :source => :child_page end

class PageRelationship < ActiveRecord::Base belongs_to :site belongs_to :parent_page, :foreign_key => :parent_page_id,

   :class_name => :page

belongs_to :child_page, :foreign_key => :child_page_id, :class_name => :page end

class Page < ActiveRecord::Base has_many :page_relationships, :foreign_key => :child_page_id

has_many :child_pages, :through => :page_relationships, :source => :child_page has_many :parent_pages, :through => :page_relationships, :source => :parent_page end

The idea being that you can have multipe sites each with their own

sitetree, and the ability to share pages between sites but in different positions in the site tree.

If I understood your domain, it is like :

Site 1 -----> SiteTree 1

Site 2 ------> SiteTree 2

and so on.

Then SiteTree has many Pages. So it looks like you have one-to-one relationship between Site and SiteTree. SiteTree and Pages many to many relationship.

If that is the case then your model should break the many-to-many relationship between SiteTree and Page classes.

Your Page model doesn’t have the right associations for a self-referential hmt relationship. You need two different has_many

assocs for the parent and child refs to the join model. This is like having different aliases for your joins in SQL. Take a look at my posting on this:

http://blog.hasmanythrough.com/articles/2006/04/21/self-referential-through

Also, your Site class has some weird named assocs. That might be the source of your error. Remember, if the model name can’t be inferred from

the assoc name, you need to specify it with options.

Edge (n) <------------------->(1) Node -----

^_____|

Is the diagram correct? Node has the self-reference and you have one to many relationship between the Node and the Edges.

Many thanks for all your help, I have now managed to fix it. After reading John's post ' Self-referential has_many :through associations' I sorted it.

Great to get such a quick response from people. First time I posted a question here! Was very happy indeed. My new models which work are as follows:

class Site < ActiveRecord::Base   has_and_belongs_to_many :users   has_many :page_relationships   has_many :pages, :through => :page_relationships, :source => :child_page end

class PageRelationship < ActiveRecord::Base   belongs_to :site   belongs_to :parent_page, :foreign_key => 'parent_page_id',         :class_name => 'Page'   belongs_to :child_page, :foreign_key => 'child_page_id',         :class_name => 'Page' end

class Page < ActiveRecord::Base   has_many :page_relationships_as_child, :foreign_key => 'child_page_id',         :class_name => 'PageRelationship'   has_many :page_relationships_as_parent, :foreign_key => 'parent_page_id',         :class_name => 'PageRelationship'   has_many :child_pages, :through => :page_relationships_as_child   has_many :parent_pages, :through => :page_relationships_as_parent end

Cheers again, Mark