Don't query the database schema when calling `serialize`

We need to decorate the types lazily. This is extracted to a separate
API, as there are other refactorings that will be able to make use of
it, and to allow unit testing the finer points more granularly.

1 files changed, 112 insertions, 0 deletions

diff --git a/activerecord/test/cases/attribute_decorators_test.rb b/activerecord/test/cases/attribute_decorators_test.rb
new file mode 100644
index 0000000000..e5c077a7a7
--- /dev/null
+++ b/activerecord/test/cases/attribute_decorators_test.rb
@@ -0,0 +1,112 @@
+require 'cases/helper'
+
+module ActiveRecord
+  class AttributeDecoratorsTest < ActiveRecord::TestCase
+    class Model < ActiveRecord::Base
+      self.table_name = 'attribute_decorators_model'
+    end
+
+    class StringDecorator < SimpleDelegator
+      def initialize(delegate, decoration = "decorated!")
+        @decoration = decoration
+        super(delegate)
+      end
+
+      def type_cast(value)
+        "#{super} #{@decoration}"
+      end
+    end
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table :attribute_decorators_model, force: true do |t|
+        t.string :a_string
+      end
+    end
+
+    teardown do
+      return unless @connection
+      @connection.execute 'DROP TABLE IF EXISTS attribute_decorators_model'
+      Model.attribute_type_decorations.clear
+      Model.reset_column_information
+    end
+
+    test "attributes can be decorated" do
+      model = Model.new(a_string: 'Hello')
+      assert_equal 'Hello', model.a_string
+
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: 'Hello')
+      assert_equal 'Hello decorated!', model.a_string
+    end
+
+    test "decoration does not eagerly load existing columns" do
+      assert_no_queries do
+        Model.reset_column_information
+        Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      end
+    end
+
+    test "undecorated columns are not touched" do
+      Model.property :another_string, Type::String.new, default: 'something or other'
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      assert_equal 'something or other', Model.new.another_string
+    end
+
+    test "decorators can be chained" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: 'Hello!')
+
+      assert_equal 'Hello! decorated! decorated!', model.a_string
+    end
+
+    test "decoration of the same type multiple times is idempotent" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: 'Hello')
+      assert_equal 'Hello decorated!', model.a_string
+    end
+
+    test "decorations occur in order of declaration" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :other) do |type|
+        StringDecorator.new(type, 'decorated again!')
+      end
+
+      model = Model.new(a_string: 'Hello!')
+
+      assert_equal 'Hello! decorated! decorated again!', model.a_string
+    end
+
+    test "decorating attributes does not modify parent classes" do
+      Model.property :another_string, Type::String.new, default: 'whatever'
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      child_class = Class.new(Model)
+      child_class.decorate_attribute_type(:another_string, :test) { |t| StringDecorator.new(t) }
+      child_class.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: 'Hello!')
+      child = child_class.new(a_string: 'Hello!')
+
+      assert_equal 'Hello! decorated!', model.a_string
+      assert_equal 'whatever', model.another_string
+      assert_equal 'Hello! decorated! decorated!', child.a_string
+      # We are round tripping the default, and we don't undo our decoration
+      assert_equal 'whatever decorated! decorated!', child.another_string
+    end
+
+    test "defaults are decorated on the column" do
+      Model.property :a_string, Type::String.new, default: 'whatever'
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      column = Model.columns_hash['a_string']
+
+      assert_equal 'whatever decorated!', column.default
+    end
+  end
+end