Add a public API to allow users to specify column types

As a result of all of the refactoring that's been done, it's now
possible for us to define a public API to allow users to specify
behavior. This is an initial implementation so that I can work off of it
in smaller pieces for additional features/refactorings.

The current behavior will continue to stay the same, though I'd like to
refactor towards the automatic schema detection being built off of this
API, and add the ability to opt out of automatic schema detection.

Use cases:

- We can deprecate a lot of the edge cases around types, now that there
  is an alternate path for users who wish to maintain the same behavior.
- I intend to refactor serialized columns to be built on top of this
  API.
- Gem and library maintainers are able to interact with `ActiveRecord`
  at a slightly lower level in a more stable way.
- Interesting ability to reverse the work flow of adding to the schema.
  Model can become the single source of truth for the structure. We can
  compare that to what the database says the schema is, diff them, and
  generate a migration.

2 files changed, 70 insertions, 0 deletions

diff --git a/activerecord/test/cases/custom_properties_test.rb b/activerecord/test/cases/custom_properties_test.rb
new file mode 100644
index 0000000000..9598f0299c
--- /dev/null
+++ b/activerecord/test/cases/custom_properties_test.rb
@@ -0,0 +1,64 @@
+require 'cases/helper'
+
+class OverloadedType < ActiveRecord::Base
+  property :overloaded_float, Type::Integer.new
+  property :overloaded_string_with_limit, Type::String.new(limit: 50)
+  property :non_existent_decimal, Type::Decimal.new
+end
+
+class UnoverloadedType < ActiveRecord::Base
+  self.table_name = 'overloaded_types'
+end
+
+module ActiveRecord
+  class CustomPropertiesTest < ActiveRecord::TestCase
+    def test_overloading_types
+      data = OverloadedType.new
+
+      data.overloaded_float = "1.1"
+      data.unoverloaded_float = "1.1"
+
+      assert_equal 1, data.overloaded_float
+      assert_equal 1.1, data.unoverloaded_float
+    end
+
+    def test_overloaded_properties_save
+      data = OverloadedType.new
+
+      data.overloaded_float = "2.2"
+      data.save!
+      data.reload
+
+      assert_equal 2, data.overloaded_float
+      assert_equal 2.0, UnoverloadedType.last.overloaded_float
+    end
+
+    def test_properties_assigned_in_constructor
+      data = OverloadedType.new(overloaded_float: '3.3')
+
+      assert_equal 3, data.overloaded_float
+    end
+
+    def test_overloaded_properties_with_limit
+      assert_equal 50, OverloadedType.columns_hash['overloaded_string_with_limit'].limit
+      assert_equal 255, UnoverloadedType.columns_hash['overloaded_string_with_limit'].limit
+    end
+
+    def test_nonexistent_property
+      data = OverloadedType.new(non_existent_decimal: 1)
+
+      assert_equal BigDecimal.new(1), data.non_existent_decimal
+      assert_raise ActiveRecord::UnknownAttributeError do
+        UnoverloadedType.new(non_existent_decimal: 1)
+      end
+    end
+
+    def test_overloaded_properties_have_no_default
+      data = OverloadedType.new
+      unoverloaded_data = UnoverloadedType.new
+
+      assert_nil data.overloaded_float
+      assert unoverloaded_data.overloaded_float
+    end
+  end
+end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index c15ee5022e..4cce58f4f4 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -855,6 +855,12 @@ ActiveRecord::Schema.define do
 
     execute "ALTER TABLE lessons_students ADD CONSTRAINT student_id_fk FOREIGN KEY (#{quote_column_name 'student_id'}) REFERENCES #{quote_table_name 'students'} (#{quote_column_name 'id'})"
   end
+
+  create_table :overloaded_types, force: true do |t|
+    t.float :overloaded_float, default: 500
+    t.float :unoverloaded_float
+    t.string :overloaded_string_with_limit, limit: 255
+  end
 end
 
 Course.connection.create_table :courses, force: true do |t|