Add has_many Debts relationship to Bet

This will help easily diplay or manipulate the Debts that are associated
with a particular Bet.

app/models/bet.rb

@@ -2,6 +2,7 @@ class Bet < ApplicationRecord
   has_many :users, through: :user_bets
   has_many :user_bets
   has_many :options, class_name: 'BetOption'
+  has_many :debts
   belongs_to :creator, class_name: 'User'
 
   validates :expires_at, presence: true
@@ -15,7 +16,8 @@ def resolve(winning_option:)
       Debt.create(
         creditor: won_bet.user,
         debtor: lost_bet.user,
-        amount:  amount_owed(lost_bet, won_bet)
+        amount:  amount_owed(lost_bet, won_bet),
+        bet: self
       )
     end
   end

app/models/debt.rb

@@ -1,4 +1,5 @@
 class Debt < ApplicationRecord
   belongs_to :debtor,   class_name: 'User'
   belongs_to :creditor, class_name: 'User'
+  belongs_to :bet, optional: true
 end

db/migrate/20170323164658_add_has_many_belongs_to_relationship_between_bet_and_debt.rb

@@ -0,0 +1,6 @@
+class AddHasManyBelongsToRelationshipBetweenBetAndDebt <
+  ActiveRecord::Migration[5.0]
+  def change
+    add_reference :debts, :bet, foreign_key: true
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170323160837) do
+ActiveRecord::Schema.define(version: 20170323164658) do
 
   create_table "bet_options", force: :cascade do |t|
     t.text     "option_text"
@@ -37,6 +37,8 @@
     t.datetime "created_at",                            null: false
     t.datetime "updated_at",                            null: false
     t.datetime "payment_date"
+    t.integer  "bet_id"
+    t.index ["bet_id"], name: "index_debts_on_bet_id"
     t.index ["creditor_id"], name: "index_debts_on_creditor_id"
     t.index ["debtor_id"], name: "index_debts_on_debtor_id"
   end