Question

I would like to model a person’s relationship to another person, where the relationship isn’t necessarily hierarchical (i.e. friends & colleagues, rather than parent & children) and I am interested in capturing more detail about each relationship (e.g. notes, type of relationship, date established). Finally, I would like to use the act_as_tree relationship to be able to navigate/diagram these relationships.

The migrations:

class CreateProfiles < ActiveRecord::Migration   def self.up
    create_table :profiles do |table|
      table.column :firstName, :string
      table.column :lastName, :string
      table.column :telephone, :string
      table.column :emailAddress, :string
      table.column :location, :string
      table.timestamps
    end   end   def self.down
    drop_table :profiles   end end

class Relationship < ActiveRecord::Migration   def self.up
    create_table :relationships, :id => false do |table|
      table.column my_id :integer
      table.column your_id :integer
      table.column relationshipType :string
      table.column dateEstablished :date
      table.column notes :text
      table.timestamps      end   end   def self.down
    drop_table :relationships   end end

The models:

class Person < ActiveRecord::Base
  has_many :relationships, :foreign_key => "my_id"
  has_many :persons :through => :relationships
end

class Relationship < ActiveRecord::Base
  belongs_to :persons
  acts_as_tree
end

Questions:

1. How do I define the relationships between these tables correctly?
2. As the my_id/your_id combination is unique, does it make sense to eliminate the :id on the relationships table?
3. Are there better names for the ‘my_id’ & ‘your_id’ fields to make use of RoR’s conventions?
4. Will I have difficulties with the act_as_tree relationship if one of the columns isn’t name ‘parent_id’?

Answer 1

1. Just a couple of days ago, a similar question was asked: “Many-to-many relationship with the same model in rails?”. I tried to document extensively how to do looped associations there. Perhaps that will help you along?

2. Tables without IDs in Rails are only ever seen with a has_and_belongs_to_many association. With regular has_many :through associations, the join table’s model is like any other ActiveRecord model, and requires an ID column

3. I’m not aware of a good convention here, but those examples are a bit strange. You’d be accessing them as relationship.your, which feels a bit awkward to me personally. Perhaps your_person_id, which would be accessed as relationship.your_person, and make clear that you’re dealing with a Person instance? Another option could be relationship.you.

4. I’ve never used acts_as_tree, but you can invoke it with a parameter like so: acts_as_tree :foreign_key => 'my_id'

As I mention in my answer to the other question, it looks like your biggest difficulty will be bi-directional relationships. Once a person A is connected to a person B, it is not implied that person B is connected to person A. That’s unfortunately difficult to accomplish in ActiveRecord, from what I can tell.