Model Question - First Rails Project

rubyonrails-talk
1

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 Development 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

2

billbell52 wrote:

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 Development 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

Try this:

http://wiki.rubyonrails.org/rails/pages/ActsAsTree

3

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