`preload` preserves readonly flag on associations. #15853

This is a partial fix for #15853. It only works when a `preload`
is issued and not an `eager_load`. I've added a skipped failing
test-case to keep in mind that we need to deal with `eager_load`.

1 files changed, 29 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 910067666a..21912fdf0f 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1261,4 +1261,33 @@ class EagerAssociationTest < ActiveRecord::TestCase
       Author.eager_load(:posts_with_signature).to_a
     end
   end
+
+  test "preloading readonly association" do
+    # has-one
+    firm = Firm.where(id: "1").preload(:readonly_account).first!
+    assert firm.readonly_account.readonly?
+
+    # has_and_belongs_to_many
+    project = Project.where(id: "2").preload(:readonly_developers).first!
+    assert project.readonly_developers.first.readonly?
+
+    # has-many :through
+    david = Author.where(id: "1").preload(:readonly_comments).first!
+    assert david.readonly_comments.first.readonly?
+  end
+
+  test "eager-loading readonly association" do
+    skip "eager_load does not yet preserve readonly associations"
+    # has-one
+    firm = Firm.where(id: "1").eager_load(:readonly_account).first!
+    assert firm.readonly_account.readonly?
+
+    # has_and_belongs_to_many
+    project = Project.where(id: "2").eager_load(:readonly_developers).first!
+    assert project.readonly_developers.first.readonly?
+
+    # has-many :through
+    david = Author.where(id: "1").eager_load(:readonly_comments).first!
+    assert david.readonly_comments.first.readonly?
+  end
 end