1 files changed, 49 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/validations/exclusion.rb b/activemodel/lib/active_model/validations/exclusion.rb
new file mode 100644
index 0000000000..3be7ab6ba8
--- /dev/null
+++ b/activemodel/lib/active_model/validations/exclusion.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+require "active_model/validations/clusivity"
+
+module ActiveModel
+  module Validations
+    class ExclusionValidator < EachValidator # :nodoc:
+      include Clusivity
+
+      def validate_each(record, attribute, value)
+        if include?(record, value)
+          record.errors.add(attribute, :exclusion, options.except(:in, :within).merge!(value: value))
+        end
+      end
+    end
+
+    module HelperMethods
+      # Validates that the value of the specified attribute is not in a
+      # particular enumerable object.
+      #
+      #   class Person < ActiveRecord::Base
+      #     validates_exclusion_of :username, in: %w( admin superuser ), message: "You don't belong here"
+      #     validates_exclusion_of :age, in: 30..60, message: 'This site is only for under 30 and over 60'
+      #     validates_exclusion_of :format, in: %w( mov avi ), message: "extension %{value} is not allowed"
+      #     validates_exclusion_of :password, in: ->(person) { [person.username, person.first_name] },
+      #                            message: 'should not be the same as your username or first name'
+      #     validates_exclusion_of :karma, in: :reserved_karmas
+      #   end
+      #
+      # Configuration options:
+      # * <tt>:in</tt> - An enumerable object of items that the value shouldn't
+      #   be part of. This can be supplied as a proc, lambda or symbol which returns an
+      #   enumerable. If the enumerable is a numerical, time or datetime range the test
+      #   is performed with <tt>Range#cover?</tt>, otherwise with <tt>include?</tt>. When
+      #   using a proc or lambda the instance under validation is passed as an argument.
+      # * <tt>:within</tt> - A synonym(or alias) for <tt>:in</tt>
+      #   <tt>Range#cover?</tt>, otherwise with <tt>include?</tt>.
+      # * <tt>:message</tt> - Specifies a custom error message (default is: "is
+      #   reserved").
+      #
+      # There is also a list of default options supported by every validator:
+      # +:if+, +:unless+, +:on+, +:allow_nil+, +:allow_blank+, and +:strict+.
+      # See <tt>ActiveModel::Validations#validates</tt> for more information
+      def validates_exclusion_of(*attr_names)
+        validates_with ExclusionValidator, _merge_attributes(attr_names)
+      end
+    end
+  end
+end