Validate key uniqueness across Key and DeployKey tables

app/models/deploy_key.rb

+require 'unique_public_key_validator'
+
 class DeployKey < ActiveRecord::Base
   belongs_to :project
 
@@ -10,6 +12,8 @@ class DeployKey < ActiveRecord::Base
             :uniqueness => true,
             :length   => { :within => 0..5000 }
 
+  validates_with UniquePublicKeyValidator
+
   before_save :set_identifier
   after_save :update_repository
   after_destroy :repository_delete_key

app/models/key.rb

+require 'unique_public_key_validator'
+
 class Key < ActiveRecord::Base
   belongs_to :user
 
@@ -10,6 +12,8 @@ class Key < ActiveRecord::Base
             :uniqueness => true,
             :length   => { :within => 0..5000 }
 
+  validates_with UniquePublicKeyValidator
+
   before_save :set_identifier
   after_save :update_repository
   after_destroy :repository_delete_key

lib/unique_public_key_validator.rb

+class UniquePublicKeyValidator < ActiveModel::Validator
+  def validate(record)
+    if (DeployKey.where('key = ? AND id !=?', record.key , record.id).count > 0 || Key.where('key = ? AND id !=?', record.key , record.id).count > 0)
+      record.errors.add :key, 'already exist.'
+    end
+  end
+end