1 files changed, 23 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
index d1469d0a7a..676b0d47d3 100644
--- a/activerecord/lib/active_record/relation/where_clause.rb
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -30,6 +30,10 @@ module ActiveRecord
           binds == other.binds
       end
 
+      def invert
+        WhereClause.new(inverted_parts, binds)
+      end
+
       def self.empty
         new([], [])
       end
@@ -60,6 +64,25 @@ module ActiveRecord
         conflicts.map! { |node| node.name.to_s }
         binds.reject { |col, _| conflicts.include?(col.name) }
       end
+
+      def inverted_parts
+        parts.map { |node| invert_predicate(node) }
+      end
+
+      def invert_predicate(node)
+        case node
+        when NilClass
+          raise ArgumentError, 'Invalid argument for .where.not(), got nil.'
+        when Arel::Nodes::In
+          Arel::Nodes::NotIn.new(node.left, node.right)
+        when Arel::Nodes::Equality
+          Arel::Nodes::NotEqual.new(node.left, node.right)
+        when String
+          Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
+        else
+          Arel::Nodes::Not.new(node)
+        end
+      end
     end
   end
 end