gistfile1.txt

            Table "public.users"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | character varying(36) | not null
Indexes:
    "users_pkey" PRIMARY KEY, btree (id)
Referenced by:
    TABLE "authentications" CONSTRAINT "authentications_user_fk" FOREIGN KEY (user_id) REFERENCES users(id)
    TABLE "delta" CONSTRAINT "delta_user_fk" FOREIGN KEY (user_id) REFERENCES users(id)
    TABLE "projects" CONSTRAINT "projects_user_fk" FOREIGN KEY (user_id) REFERENCES users(id)



           Table "public.projects"
 Column  |         Type          | Modifiers 
---------+-----------------------+-----------
 id      | character varying(36) | not null
 name    | character varying(50) | not null
 user_id | character varying(36) | not null
Indexes:
    "projects_pkey" PRIMARY KEY, btree (id)
    "unique_projects_user_project" UNIQUE, btree (name)
    "index_projects_user" btree (user_id)
Foreign-key constraints:
    "projects_user_fk" FOREIGN KEY (user_id) REFERENCES users(id)
Referenced by:
    TABLE "branches" CONSTRAINT "branches_project_fk" FOREIGN KEY (project_id) REFERENCES projects(id)



              Table "public.branches"
     Column     |         Type          | Modifiers 
----------------+-----------------------+-----------
 id             | character varying(36) | not null
 name           | character varying(50) | not null
 project_id     | character varying(36) | not null
 forked_from_id | character varying(36) | 
Indexes:
    "branches_pkey" PRIMARY KEY, btree (id)
    "unique_branches_project_version" UNIQUE, btree (name)
    "index_branches_forked_from" btree (forked_from_id)
    "index_branches_project" btree (project_id)
Foreign-key constraints:
    "branches_forked_from_fk" FOREIGN KEY (forked_from_id) REFERENCES revisions(id)
    "branches_project_fk" FOREIGN KEY (project_id) REFERENCES projects(id)
Referenced by:
    TABLE "revisions" CONSTRAINT "revisions_branch_fk" FOREIGN KEY (branch_id) REFERENCES branches(id)



               Table "public.revisions"
   Column    |            Type             | Modifiers 
-------------+-----------------------------+-----------
 id          | character varying(36)       | not null
 created_at  | timestamp without time zone | not null
 branch_id   | character varying(36)       | not null
 merge_of_id | character varying(36)       | 
Indexes:
    "revisions_pkey" PRIMARY KEY, btree (id)
    "index_revisions_branch" btree (branch_id)
    "index_revisions_merge_of" btree (merge_of_id)
Foreign-key constraints:
    "revisions_branch_fk" FOREIGN KEY (branch_id) REFERENCES branches(id)
    "revisions_merge_of_fk" FOREIGN KEY (merge_of_id) REFERENCES revisions(id)
Referenced by:
    TABLE "branches" CONSTRAINT "branches_forked_from_fk" FOREIGN KEY (forked_from_id) REFERENCES revisions(id)
    TABLE "delta" CONSTRAINT "delta_revision_fk" FOREIGN KEY (revision_id) REFERENCES revisions(id)
    TABLE "revisions" CONSTRAINT "revisions_merge_of_fk" FOREIGN KEY (merge_of_id) REFERENCES revisions(id)



                                      Table "public.delta"
   Column    |         Type          |                        Modifiers                         
-------------+-----------------------+----------------------------------------------------------
 id          | character varying(36) | not null
 sequence    | integer               | not null default nextval('delta_sequence_seq'::regclass)
 revision_id | character varying(36) | not null
 user_id     | character varying(36) | not null
Indexes:
    "delta_pkey" PRIMARY KEY, btree (id)
    "index_delta_revision" btree (revision_id)
    "index_delta_user" btree (user_id)
Foreign-key constraints:
    "delta_revision_fk" FOREIGN KEY (revision_id) REFERENCES revisions(id)
    "delta_user_fk" FOREIGN KEY (user_id) REFERENCES users(id)

ProjectVersions.rb

require 'uuidtools'

class User
  include DataMapper::Resource

  property :id, UUID, :key => true, :required => true, :default => proc { UUIDTools::UUID.random_create }

  has n, :projects
  has n, :deltas
end


class Project
  include DataMapper::Resource

  property :id, UUID, :key => true, :required => true, :default => proc { UUIDTools::UUID.random_create.to_s }

  property :name, String, :required => true, :unique_index => :user_project
  belongs_to :user, :unique_index => :user_project
  has n, :branches        # Project has Branch
  
  def master
    Branch.first_or_create(:project => self, :name => 'master')
  end
end

class Branch
  include DataMapper::Resource

  property :id, UUID, :key => true, :required => true, :default => proc { UUIDTools::UUID.random_create.to_s }

  belongs_to :project, :unique_index => :project_version
  property :name, String, :required => true, :unique_index => :project_version

  has n, :revisions      # Branch has Revision

  #  Branch but may originate as a fork of another user's revision of a different project:
  belongs_to :forked_from, 'Revision', :required => false
end

class Revision
  include DataMapper::Resource

  property :id, UUID, :key => true, :required => true, :default => proc { UUIDTools::UUID.random_create.to_s }
  property :created_at, DateTime, :required => true

  belongs_to :branch    # Revision belongs to Branch
  belongs_to :merge_of, Revision, :required => false
  
  has n, :deltas        # Revision includes Delta
  has n, :forks, 'Branch'# Branch is forked from Revision

  # In GIT, a revision may merge multiple other revisions in one go; not here
  belongs_to :merge_of, 'Revision', :required => false
end

class Delta
  include DataMapper::Resource
  
  property :id, UUID, :key => true, :required => true, :default => proc { UUIDTools::UUID.random_create }
  property :sequence, Serial, :key => false, :required => true
  
  belongs_to :revision  # Delta adds to Revision
  belongs_to :user      # Delta was made by User
end