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Ignores a default subclass when `becomes(Parent)` #30535

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merged 1 commit into from Jan 22, 2018

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@leonelgalan
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leonelgalan commented Sep 6, 2017

Summary

Fixes issue described in #30399: A default value on the
inheritance column prevented child.becomes(Parent) to return
an instance of Parent as expected, instead it returns an instance
of the default subclass.

The change was introduced by #17169 and it was meant to affect
initialization, alone. Where Parent.new is expected to return
an instance of the default subclass.

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rails-bot commented Sep 6, 2017

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @schneems (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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leonelgalan commented Dec 6, 2017

After the original issue was marked as stale I've confirmed this is still an issue in Rails 5.1.4 and 5.2.0.beta2. I rebased this PR to make it easier for reviewers.

activerecord/lib/active_record/persistence.rb Outdated
became = klass.new(klass.inheritance_column => klass.name)
else
became = klass.new
end

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@kamipo

kamipo Jan 7, 2018

Member

How about avoiding klass.new simply?

diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 462e5e7aaf..e5fa4a925e 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -359,7 +359,8 @@ def destroy!
     # Any change to the attributes on either instance will affect both instances.
     # If you want to change the sti column as well, use #becomes! instead.
     def becomes(klass)
-      became = klass.new
+      became = klass.allocate
+      became.send(:initialize)
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@mutations_from_database", @mutations_from_database) if defined?(@mutations_from_database)
       became.instance_variable_set("@changed_attributes", attributes_changed_by_setter)

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@leonelgalan

leonelgalan Jan 15, 2018

Contributor

I'm not familiar with the cons of klass.new and using klass.allocate and initialize instead. Let me read more about it and I'll change the code.

Your proposed change works (with the attached tests: Issue and PR), from what I've read rarely you want to handle allocation and initialization on your own and you should rely on .new instead. Is this one of these cases? I'll make the change if it's OK with you guys.

@kamipo kamipo added the activerecord label Jan 7, 2018

@kamipo kamipo assigned kamipo and unassigned schneems Jan 7, 2018

@kamipo

kamipo approved these changes Jan 22, 2018

Looks good to me. Can you squash your commits into one?

Ignores a default subclass when `becomes(Parent)`
Fixes issue described in #30399: A default value on the
inheritance column prevented `child.becomes(Parent)` to return
an instance of `Parent` as expected, instead it returns an instance
of the default subclass.

The change was introduced by #17169 and it was meant to affect
initialization, alone. Where `Parent.new` is expected to return
an instance of the default subclass.

@leonelgalan leonelgalan force-pushed the leonelgalan:becomes_and_default_inheritance branch to 3562331 Jan 22, 2018

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leonelgalan commented Jan 22, 2018

Squashed and rebased, thanks for your help!

@kamipo kamipo merged commit c177bca into rails:master Jan 22, 2018

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