Self Reference, Almost There (I Hope!)

Rails
1

I’m still struggling with the self reference. I THINK I’m getting
close. I have the following tables:

class CreateCategories < ActiveRecord::Migration
def self.up
create_table :categories do |t|
t.string :name, :limit => 40
t.timestamps
end
end
end

class CreateRelationships < ActiveRecord::Migration
def self.up
create_table :relationships, :id => false do |t|
t.integer :category_id
t.integer :parent_id
t.integer :sort_order
t.timestamps
end
end
end

My models look like this:

class Relationship < ActiveRecord::Base
belongs_to :category, :class_name => ‘Category’,
:foreign_key => ‘category_id’
belongs_to :parent, :class_name => ‘Category’,
:foreign_key => 'parent_id
end

class Category < ActiveRecord::Base
has_many :relationships, :foreign_key => ‘category_id’

has_many :parents, :class_name => ‘Category’,
:through => ‘relationships’,
:source => :parent

has_many :children, :class_name => ‘Category’,
:through => ‘relationships’,
:source => :category
end

I can create a category. When I try to add a parent to it (e.g.
c.parents << p) I get the error

ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the
association “relationships” in model Category

I’m sure that I’m missing something simple, but I don’t see it. Can
anyone let me know what I’m missing?

Thanks much
—Michael

2

On 20 June 2010 19:12, Michael S. [email protected] wrote:

class CreateRelationships < ActiveRecord::Migration
def self.up
create_table :relationships, :id => false do |t|
t.integer :category_id
t.integer :parent_id
t.integer :sort_order
t.timestamps
end
end
end

If “relationships” is a join table, then it can’t have any fields
other than the two foreign keys.

class Relationship < ActiveRecord::Base
belongs_to :category, :class_name => ‘Category’,
:foreign_key => ‘category_id’
belongs_to :parent, :class_name => ‘Category’,
:foreign_key => 'parent_id
end

Right - so Relationship is an AR model - it needs an ID column.

There might be some other issues… but get to them after the
Relationship models are working (try creating one in the console to
make sure it works…)

3

On 20/06/2010 20:18, Michael P. wrote:

end

Right - so Relationship is an AR model - it needs an ID column.

Also, you need to refer to the relationships association in the Category
class as follows:

has_many :parents, :class_name => ‘Category’, :through =>
:relationships, :source => :parent

(In case there’s anybody still interested :slight_smile: )