Also support writing the hstore back to the database

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -476,6 +476,11 @@ module ActiveRecord
         return super unless column
 
         case value
+        when Hash
+          case column.sql_type
+          when 'hstore' then super(PostgreSQLColumn.hstore_to_string(value), column)
+          else super
+          end
         when Float
           return super unless value.infinite? && column.type == :datetime
           "'#{value.to_s.downcase}'"

activerecord/test/cases/adapters/postgresql/hstore_test.rb

@@ -86,6 +86,14 @@ class PostgresqlHstoreTest < ActiveRecord::TestCase
     assert_equal({"\"a"=>"q\"w"}, @column.type_cast('\"a=>q"w'))
   end
 
+  def test_rewrite
+    @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
+    x = Hstore.find :first
+    x.tags = { '"a\'' => 'b' }
+    assert x.save!
+  end
+
+
   def test_select
     @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
     x = Hstore.find :first