I am trying to do my first Rails project. I am having a problem understanding how to create the model. The project will track parts that are used in building an item. It will be hierarchical. For example a bicycle wheel is made from spokes, tire, rim and hub. A bicycle is made up of 2 wheels. Different bicycles will use different combinations of wheels. I am using the book "Agile Web D. Using Rails" and the model I have so far is below. This case is not covered in the book. Are there any good examples of this out there. I am sure this is a common problem. Here are the tables. create_table :parts do |t| t.column :name, :string, :limit => 255, :null => false t.column :version, :integer, :null => false t.column :create_date, :timestamp, :null => false t.column :description, :text end create_table :uses, :id => false do |t| t.column :part_id, :integer, :null => false t.column :part_parent_id, :integer, :null => false t.column :count, :integer, :null => false end I want to be able traverse up and down the hierarchy. Is this close to what I need? class Part < ActiveRecord::Base has_many :used_by, :class_name => 'Use', :foreign_key => "part_id" has_many :parents, :through => :used_by, :class_name => 'Part', :foreign_key => "part_parent_id" has_many :uses, :class_name => 'Use', :foreign_key => 'part_parent_id' has_many :parts, :through => :uses, :class_name => 'Use', :foreign_key => "part_id" end class Use < ActiveRecord::Base belongs_to :parent, :class_name => 'Part', :source => :part_parent_id belongs_to :child, :class_name => 'Part', :source => :part_id end
on 2007-03-13 22:48
on 2007-03-13 22:52
billbell52 wrote: > problem. Here are the tables. > t.column :part_id, :integer, :null => false > 'Part', :foreign_key => "part_parent_id" > end Try this: http://wiki.rubyonrails.org/rails/pages/ActsAsTree -- Michael W.
on 2007-03-15 03:27
Bill, I'm new to this site and typically just read everyone else's posts, but in this case I think I can help you with your bicycle metaphor. I come from a manufacturing background and we construct bicycles using a 'Bill of Material'. This is simple a parent record for each 'build' build that looks like this; BOM PartNo_id Quantity (other fields if you want to get fancy) The PartNo table obviously has id Descr Qty on hand, etc. David