run `type` column through attribtues API type casting.

Closes #21986.

This makes it possible to write custom types that define a different
mapping for STI columns.

3 files changed, 84 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 3d251f95cc..81027eab82 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   Run `type` attributes through attributes API type-casting before
+    instantiating the corresponding subclass. This makes it possible to define
+    custom STI mappings.
+
+    Fixes #21986.
+
+    *Yves Senn*
+
 *   Add expression support on the schema default.
 
     Example:
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index 6259c4cd33..3a17f74b1d 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -167,6 +167,7 @@ module ActiveRecord
       end
 
       def find_sti_class(type_name)
+        type_name = base_class.type_for_attribute(inheritance_column).cast(type_name)
         subclass = begin
           if store_full_sti_class
             ActiveSupport::Dependencies.constantize(type_name)
diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index 03bce547da..e97275a97b 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -7,6 +7,7 @@ require 'models/project'
 require 'models/subscriber'
 require 'models/vegetables'
 require 'models/shop'
+require 'models/sponsor'
 
 module InheritanceTestHelper
   def with_store_full_sti_class(&block)
@@ -524,3 +525,77 @@ class InheritanceAttributeTest < ActiveRecord::TestCase
     assert_instance_of Empire, empire
   end
 end
+
+class InheritanceAttributeMappingTest < ActiveRecord::TestCase
+  setup do
+    @old_registry = ActiveRecord::Type.registry
+    ActiveRecord::Type.registry = ActiveRecord::Type::AdapterSpecificRegistry.new
+    ActiveRecord::Type.register :omg_sti, InheritanceAttributeMappingTest::OmgStiType
+    Company.delete_all
+    Sponsor.delete_all
+  end
+
+  teardown do
+    ActiveRecord::Type.registry = @old_registry
+  end
+
+  class OmgStiType < ActiveRecord::Type::String
+    def cast_value(value)
+      if value =~ /\Aomg_(.+)\z/
+        $1.classify
+      else
+        value
+      end
+    end
+
+    def serialize(value)
+      if value
+        "omg_%s" % value.underscore
+      end
+    end
+  end
+
+  class Company < ActiveRecord::Base
+    self.table_name = 'companies'
+    attribute :type, :omg_sti
+  end
+
+  class Startup < Company; end
+  class Empire < Company; end
+
+  class Sponsor < ActiveRecord::Base
+    self.table_name = 'sponsors'
+    attribute :sponsorable_type, :omg_sti
+
+    belongs_to :sponsorable, polymorphic: true
+  end
+
+  def test_sti_with_custom_type
+    Startup.create! name: 'a Startup'
+    Empire.create! name: 'an Empire'
+
+    assert_equal [["a Startup", "omg_inheritance_attribute_mapping_test/startup"],
+                  ["an Empire", "omg_inheritance_attribute_mapping_test/empire"]], ActiveRecord::Base.connection.select_rows('SELECT name, type FROM companies')
+    assert_equal [["a Startup", "InheritanceAttributeMappingTest::Startup"],
+                  ["an Empire", "InheritanceAttributeMappingTest::Empire"]], Company.all.map { |a| [a.name, a.type] }
+
+    startup = Startup.first
+    startup.becomes! Empire
+    startup.save!
+
+    assert_equal [["a Startup", "omg_inheritance_attribute_mapping_test/empire"],
+                  ["an Empire", "omg_inheritance_attribute_mapping_test/empire"]], ActiveRecord::Base.connection.select_rows('SELECT name, type FROM companies')
+    assert_equal [["a Startup", "InheritanceAttributeMappingTest::Empire"],
+                  ["an Empire", "InheritanceAttributeMappingTest::Empire"]], Company.all.map { |a| [a.name, a.type] }
+  end
+
+  def test_polymorphic_associations_custom_type
+    startup = Startup.create! name: 'a Startup'
+    sponsor = Sponsor.create! sponsorable: startup
+
+    assert_equal ["omg_inheritance_attribute_mapping_test/company"], ActiveRecord::Base.connection.select_values('SELECT sponsorable_type FROM sponsors')
+
+    sponsor = Sponsor.first
+    assert_equal startup, sponsor.sponsorable
+  end
+end