From f0ddf87e4bfcfcb861b0a9dca32edb733668bd30 Mon Sep 17 00:00:00 2001
From: Sean Griffin <sean@seantheprogrammer.com>
Date: Mon, 25 Jul 2016 11:06:04 -0400
Subject: Correct the behavior of virtual attributes on models loaded from the
 db

Previously we had primarily tested the behavior of these attributes by
calling `.new`, allowing this to slip through the cracks. There were a
few ways in which they were behaving incorrectly.

The biggest issue was that attempting to read the attribute would
through a `MissingAttribute` error. We've corrected this by returning
the default value when the attribute isn't backed by a database column.
This is super special cased, but I don't see a way to avoid this
conditional. I had considered handling this higher up in
`define_default_attribute`, but we don't have the relevant information
there as users can provide new defaults for database columns as well.

Once I corrected this, I had noticed that the attributes were always
being marked as changed. This is because the behavior of
`define_default_attribute` was treating them as assigned from
`Attribute::Null`.

Finally, with our new implementation, `LazyAttributeHash` could no
longer be marshalled, as it holds onto a proc. This has been corrected
as well. I've not handled YAML in that class, as we do additional work
higher up to avoid YAML dumping it at all.

Fixes #25787
Close #25841
---
 activerecord/test/cases/attributes_test.rb | 44 ++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

(limited to 'activerecord/test')

diff --git a/activerecord/test/cases/attributes_test.rb b/activerecord/test/cases/attributes_test.rb
index 7bcaa53aa2..604411da97 100644
--- a/activerecord/test/cases/attributes_test.rb
+++ b/activerecord/test/cases/attributes_test.rb
@@ -205,5 +205,49 @@ module ActiveRecord
 
       assert_equal(:bar, child.new(foo: :bar).foo)
     end
+
+    test "attributes not backed by database columns are not dirty when unchanged" do
+      refute OverloadedType.new.non_existent_decimal_changed?
+    end
+
+    test "attributes not backed by database columns are always initialized" do
+      OverloadedType.create!
+      model = OverloadedType.first
+
+      assert_nil model.non_existent_decimal
+      model.non_existent_decimal = "123"
+      assert_equal 123, model.non_existent_decimal
+    end
+
+    test "attributes not backed by database columns return the default on models loaded from database" do
+      child = Class.new(OverloadedType) do
+        attribute :non_existent_decimal, :decimal, default: 123
+      end
+      child.create!
+      model = child.first
+
+      assert_equal 123, model.non_existent_decimal
+    end
+
+    test "attributes not backed by database columns properly interact with mutation and dirty" do
+      child = Class.new(ActiveRecord::Base) do
+        self.table_name = "topics"
+        attribute :foo, :string, default: "lol"
+      end
+      child.create!
+      model = child.first
+
+      assert_equal "lol", model.foo
+
+      model.foo << "asdf"
+      assert_equal "lolasdf", model.foo
+      assert model.foo_changed?
+
+      model.reload
+      assert_equal "lol", model.foo
+
+      model.foo = "lol"
+      refute model.changed?
+    end
   end
 end
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