Expose an `invert_where` method that will invert all scope conditions.

```ruby
class User
  scope :active, -> { where(accepted: true, locked: false) }
end

User.active

User.active.invert_where
```

activerecord/CHANGELOG.md

@@ -1,3 +1,19 @@
+*   Expose an `invert_where` method that will invert all scope conditions.
+
+    ```ruby
+    class User
+      scope :active, -> { where(accepted: true, locked: false) }
+    end
+
+    User.active
+    # ... WHERE `accepted` = 1 AND `locked` = 0
+
+    User.active.invert_where
+    # ... WHERE NOT (`accepted` = 1 AND `locked` = 0)
+    ```
+
+    *Kevin Deisz*
+
 *   Restore possibility of passing `false` to :polymorphic option of `belongs_to`.
 
     Previously, passing `false` would trigger the option validation logic

activerecord/lib/active_record/querying.rb

@@ -13,7 +13,7 @@ module ActiveRecord
       :destroy_all, :delete_all, :update_all, :touch_all, :destroy_by, :delete_by,
       :find_each, :find_in_batches, :in_batches,
       :select, :reselect, :order, :reorder, :group, :limit, :offset, :joins, :left_joins, :left_outer_joins,
-      :where, :rewhere, :preload, :extract_associated, :eager_load, :includes, :from, :lock, :readonly,
+      :where, :rewhere, :invert_where, :preload, :extract_associated, :eager_load, :includes, :from, :lock, :readonly,
       :and, :or, :annotate, :optimizer_hints, :extending,
       :having, :create_with, :distinct, :references, :none, :unscope, :merge, :except, :only,
       :count, :average, :minimum, :maximum, :sum, :calculate,

activerecord/lib/active_record/relation/query_methods.rb

@@ -693,6 +693,32 @@ module ActiveRecord
       scope
     end
 
+    # Allows you to invert an entire where clause instead of manually applying conditions.
+    #
+    #   class User
+    #     scope :active, -> { where(accepted: true, locked: false) }
+    #   end
+    #
+    #   User.where(accepted: true)
+    #   # WHERE `accepted` = 1
+    #
+    #   User.where(accepted: true).invert_where
+    #   # WHERE `accepted` != 1
+    #
+    #   User.active
+    #   # WHERE `accepted` = 1 AND `locked` = 0
+    #
+    #   User.active.invert_where
+    #   # WHERE NOT (`accepted` = 1 AND `locked` = 0)
+    def invert_where
+      spawn.invert_where!
+    end
+
+    def invert_where! # :nodoc:
+      self.where_clause = where_clause.invert
+      self
+    end
+
     # Returns a new relation, which is the logical intersection of this relation and the one passed
     # as an argument.
     #

activerecord/test/cases/relation/where_test.rb

@@ -425,5 +425,12 @@ module ActiveRecord
     def test_where_with_unsupported_arguments
       assert_raises(ArgumentError) { Author.where(42) }
     end
+
+    def test_invert_where
+      author = authors(:david)
+      posts = author.posts.where.not(id: 1)
+
+      assert_equal 1, posts.invert_where.first.id
+    end
   end
 end