added relationship model

app/models/relationship.rb

@@ -0,0 +1,2 @@
+class Relationship < ActiveRecord::Base
+end

db/migrate/20141130130221_create_relationships.rb

@@ -0,0 +1,14 @@
+class CreateRelationships < ActiveRecord::Migration
+  def change
+    create_table :relationships do |t|
+      t.integer :source_id
+      t.integer :target_id
+
+      t.timestamps
+    end
+
+    add_index :relationships, :source_id
+    add_index :relationships, :target_id
+    add_index :relationships, [:source_id, :target_id], unique: true
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20141129211448) do
+ActiveRecord::Schema.define(version: 20141130130221) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -59,6 +59,17 @@ ActiveRecord::Schema.define(version: 20141129211448) do
 
   add_index "questions", ["user_id", "created_at"], name: "index_questions_on_user_id_and_created_at", using: :btree
 
+  create_table "relationships", force: true do |t|
+    t.integer  "source_id"
+    t.integer  "target_id"
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
+  add_index "relationships", ["source_id", "target_id"], name: "index_relationships_on_source_id_and_target_id", unique: true, using: :btree
+  add_index "relationships", ["source_id"], name: "index_relationships_on_source_id", using: :btree
+  add_index "relationships", ["target_id"], name: "index_relationships_on_target_id", using: :btree
+
   create_table "users", force: true do |t|
     t.string   "email",                  default: "",    null: false
     t.string   "encrypted_password",     default: "",    null: false