Keep column defaults in type cast form

The contract of `_field_changed?` assumes that the old value is always
type cast. That is not the case for the value in `Column#default` as
things are today. It appears there are other public methods that
assume that `Column#default` is type cast, as well. The reason for this
change originally was because the value gets put into `@raw_attributes`
in initialize. This reverts to the old behavior on `Column`, and updates
`initialize` to make sure that the values are in the right format.

activerecord/lib/active_record/connection_adapters/column.rb

@@ -52,7 +52,7 @@ module ActiveRecord
       end
 
       def extract_default(default)
-        type_cast_for_write(type_cast(default))
+        type_cast(default)
       end
     end
   end

activerecord/lib/active_record/core.rb

@@ -249,7 +249,7 @@ module ActiveRecord
     #   # Instantiates a single new object
     #   User.new(first_name: 'Jamie')
     def initialize(attributes = nil, options = {})
-      defaults = self.class.column_defaults.dup
+      defaults = self.class.raw_column_defaults.dup
       defaults.each { |k, v| defaults[k] = v.dup if v.duplicable? }
 
       @raw_attributes = defaults

activerecord/lib/active_record/model_schema.rb

@@ -241,6 +241,14 @@ module ActiveRecord
         @column_defaults ||= Hash[columns.map { |c| [c.name, c.default] }]
       end
 
+      # Returns a hash where the keys are the column names and the values
+      # are the default values suitable for use in `@raw_attriubtes`
+      def raw_column_defaults # :nodoc:
+        @raw_column_defauts ||= Hash[column_defaults.map { |name, default|
+          [name, columns_hash[name].type_cast_for_write(default)]
+        }]
+      end
+
       # Returns an array of column names as strings.
       def column_names
         @column_names ||= columns.map { |column| column.name }
@@ -285,6 +293,7 @@ module ActiveRecord
 
         @arel_engine             = nil
         @column_defaults         = nil
+        @raw_column_defauts      = nil
         @column_names            = nil
         @column_types            = nil
         @content_columns         = nil

activerecord/lib/active_record/properties.rb

@@ -113,6 +113,7 @@ module ActiveRecord
         @columns_hash = nil
         @column_types = nil
         @column_defaults = nil
+        @raw_column_defaults = nil
         @column_names = nil
         @content_columns = nil
       end

activerecord/test/cases/dirty_test.rb

@@ -616,6 +616,34 @@ class DirtyTest < ActiveRecord::TestCase
     end
   end
 
+  test "defaults with type that implements `type_cast_for_write`" do
+    type = Class.new(ActiveRecord::Type::Value) do
+      def type_cast(value)
+        value.to_i
+      end
+
+      def type_cast_for_write(value)
+        value.to_s
+      end
+
+      alias type_cast_for_database type_cast_for_write
+    end
+
+    model_class = Class.new(ActiveRecord::Base) do
+      self.table_name = 'numeric_data'
+      property :foo, type.new, default: 1
+    end
+
+    model = model_class.new
+    assert_not model.foo_changed?
+
+    model = model_class.new(foo: 1)
+    assert_not model.foo_changed?
+
+    model = model_class.new(foo: '1')
+    assert_not model.foo_changed?
+  end
+
   private
     def with_partial_writes(klass, on = true)
       old = klass.partial_writes?