Don't attempt to save dirty attributes which are not persistable

This sets a precident for how we handle `attribute` calls, which aren't
backed by a database column. We should not take this as a conscious
decision on how to handle them, and this can change when we make
`attribute` public if we have better ideas in the future.

As the composed attributes API gets fleshed out, I expect the
`persistable_attributes` method to change to
`@attributes.select(&:persistable).keys`, or some more performant
variant there-of. This can probably go away completely once we fully
move dirty checking into the attribute objects once it gets moved up to
Active Model.

Fixes #18407

1 files changed, 13 insertions, 0 deletions

diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 5b71bd7e67..ae4a8aab2c 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -708,6 +708,19 @@ class DirtyTest < ActiveRecord::TestCase
     assert model.first_name_changed?
   end
 
+  test "attribute_will_change! doesn't try to save non-persistable attributes" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'people'
+      attribute :non_persisted_attribute, ActiveRecord::Type::String.new
+    end
+
+    record = klass.new(first_name: "Sean")
+    record.non_persisted_attribute_will_change!
+
+    assert record.non_persisted_attribute_changed?
+    assert record.save
+  end
+
   private
     def with_partial_writes(klass, on = true)
       old = klass.partial_writes?