Add spec to test embedded documents changes in parent's history

[mpetazzoni]

Demonstrates #187.

[mongoid-bot]

	1 Warning
⚠️	Unless you’re refactoring existing code, please update CHANGELOG.md.

	1 Message
📖	We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!

Here's an example of a CHANGELOG.md entry:

* [#188](https://github.com/mongoid/mongoid-history/pull/188): Add spec to test embedded documents changes in parent's history - [@mpetazzoni](https://github.com/mpetazzoni).

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[dblock]

This one failed because of rubocop, so rubocop -a ; rubocop --auto-gen-config. Make the spec fail in the way it fails in your bug report.

[mpetazzoni]

Running rubocop -a finds close to 200 offenses over the whole source tree. rubocop --auto-gen-config finds about 675. Both somehow modify a bunch of files in the source tree. Am I missing some configuration?

Anyway, running bundle exec rake (which is what the continuous build is doing) correctly only show only the errors in my file. I've updated the commit.

[coveralls]

Coverage decreased (-0.03%) to 99.72% when pulling 1f34a85 on mpetazzoni:embedded-document-history-in-parent into c641447 on mongoid:master.

[dblock]

I played with this, and it's definitely a bug. In short, when the parent is saved, changes doesn't include the changes from the child relation during update, however it does include it during insert. I am not sure how to fix this, maybe @jagdeepsingh who wrote embedded support or @jnfeinstein who added some improvements on top could take a look?

[jagdeepsingh]

@mpetazzoni i appreciate the research done on this bug. I will try to look into the cause.

[mpetazzoni]

Thanks @dblock and @jagdeepsingh, appreciated. Unfortunately I don't know enough about Rails and Mongoid to fix this myself; there's way too much magic going on and I couldn't figure out whether I was missing something in the way my models were setup, or if something was missing in mongoid-history's code. Looking forward to hearing back from you on this soon, hopefully with a fix😄 !

[mateuspontes]

def modified_attributes_for_update
     @modified_attributes_for_update ||= Mongoid::History::Attributes::Update.new(self).attributes
end

always returns nil when you update only the child.

[jagdeepsingh]

Yes, @mateuspontes as i posted here, this is because the changes hash remains empty if we update only the embedded relations AND we are not using any code/gem to track changes in them.

[mateuspontes]

@jagdeepsingh in create we track changes on embedded relations, can we use the same aproach to catch changes on update?

[mateuspontes]

I'll create a new PR with a new aproach to solve this without extra gems, this is working with embed_one only for now. It's a WIP

[#<Tracker _id: 58efcf927ce04a71b049aac4, created_at: 2017-04-13 19:20:50 UTC, updated_at: 2017-04-13 19:20:50 UTC, association_chain: [{"name"=>"Parent", "id"=>BSON::ObjectId('58efcf927ce04a71b049aac5')}], modified: {"name"=>"bowser", "child"=>{"_id"=>BSON::ObjectId('58efcf927ce04a71b049aac6'), "name"=>"todd"}}, original: {}, version: 1, action: "create", scope: "parent", modifier_id: nil>, #<Tracker _id: 58efcf927ce04a71b049aac7, created_at: 2017-04-13 19:20:50 UTC, updated_at: 2017-04-13 19:20:50 UTC, association_chain: [{"name"=>"Parent", "id"=>BSON::ObjectId('58efcf927ce04a71b049aac5')}], modified: {"name"=>"brow"}, original: {"name"=>"bowser", "child"=>{}}, version: 2, action: "update", scope: "parent", modifier_id: nil>, #<Tracker _id: 58efcf927ce04a71b049aac8, created_at: 2017-04-13 19:20:50 UTC, updated_at: 2017-04-13 19:20:50 UTC, association_chain: [{"name"=>"Parent", "id"=>BSON::ObjectId('58efcf927ce04a71b049aac5')}], modified: {"child"=>{"name"=>"mario"}}, original: {"child"=>{"name"=>"todd"}}, version: 3, action: "update", scope: "parent", modifier_id: nil>]