Add validations

app/models/client.rb

@@ -12,6 +12,9 @@
 class Client < ActiveRecord::Base
   before_create :generate_key
 
+  validates :name, presence: true, uniqueness: true
+  validates :key, presence: true, uniqueness: true
+
   def transactions
     Transaction.where(origin: name)
   end

app/models/transaction.rb

@@ -19,13 +19,21 @@ class Transaction < ActiveRecord::Base
   after_save    :recalculate_balances
   after_destroy :recalculate_balances
 
+  validates :amount, numericality: { greater_than: 0 }
+  validate :different_debtor_creditor
+
   def client
     Client.find_by name: origin
   end
 
   private
+
   def recalculate_balances
     creditor.calculate_balance!
     debtor.calculate_balance!
   end
+
+  def different_debtor_creditor
+    self.errors.add :base, "Can't write money to yourself" if self.debtor == self.creditor
+  end
 end

app/models/user.rb

@@ -17,6 +17,9 @@ class User < ActiveRecord::Base
   has_many :outgoing_transactions,
     class_name: 'Transaction', foreign_key: 'debtor_id'
 
+  validates :name, presence: true, uniqueness: true
+  validates :balance, presence: true
+
   def transactions
     Transaction.where("creditor_id = ? OR debtor_id = ?", id, id)
   end