Magento2: Deleting a configurable child breaks cart and checkout pages that contained it.

[drew7721]

Preconditions (*)

1. Magento 2.3.4 | 2.3.3 | 2.2.10 (reproduces on these versions)
2. PHP 7.2.27
3. MySQL 5.7

Steps to reproduce (*)

1. Fresh install of Magento 2 (with sample data if needed)
2. Add a configurable product to the cart ( the simple child product will be added https://i.imgur.com/vBVqHNY.png )
3. Go to the Admin panel and delete the child product that you added to the cart in step 2.
4. Note that deleting the product changed the database table quote_item from
   to
   
5. See how the parent configurable is still in the quote_item table.
6. The checkout/cart and checkout page are broken and return a blank white page.

Notes, remarks and possible solutions.

1. Sales rule condition

The problem is that the product is no longer found. So the sales rule condition is breaking the page.
For instance, if this line (68) would be set to $validated = true; //$cond->validate($item); https://github.com/magento/magento2/blob/8628eb8b346ea7adceca720f04f04d9f5474da7c/app/code/Magento/SalesRule/Model/Rule/Condition/Product/Found.php#L67-L70 we would then get this page

2. Database

Note that this also leaves lots of data in the database. not only does it not clean the quote_item table properly but it does not remove the linked data from the quote_item_option table either.
This causes these tables to be very large for no reason. In my case more than 1.5M rows could be deleted.

3. Quote Plugin

https://github.com/magento/magento2/blob/8628eb8b346ea7adceca720f04f04d9f5474da7c/app/code/Magento/Quote/Model/Product/QuoteItemsCleaner.php#L26-L32

This plugin does is responsible for cleaning the table but does a half job since the parent configurable product will not be removed from the quotes and hence the cause of this bug. In my opinion, this delete should be done by sku so that all the product get removed. In this case, an index would be required on the sku column.

4. Foreign Keys and Cascade

A better fix for this would be to add a foreign key constraint on the quote_item table with the catalog_product_entity table and cascade on delete. That would completely remove the need for that plugin and all the code that it involves. I'm curious to see comments regarding this. I'm really asking myself why the decision was made to use a plugin in this case.

Also, some third party vendors bypass the plugins and events thrown by this method and hence leave an even bigger mess in the db. For instance, using a module such as RapidFlow to remove products will not trigger the plugins nor the event thrown by this method.
https://github.com/magento/magento2/blob/8628eb8b346ea7adceca720f04f04d9f5474da7c/app/code/Magento/Catalog/Model/ResourceModel/Product.php#L369-L377
One more reason why I believe this should be fixed with a database foreign key and probably an additional index on the sku column.

Expected result (*)

1. It should show the cart and it should properly clean the quotes to not maintain dead data in the quote_item table.
2. At least, it should show the cart with the error message so that the customer can remove the item from the cart or edit the configuration options.
3. It should remove the parent configurable products from the quote as well and not leave outdated data in the quote tables.

Actual result (*)

1. Cart and Checkout pages are broken
2. Database quote tables are polluted with deprecated data.

[m2-assistant[bot]]

Hi @drew7721. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

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[drew7721]

After looking into this, it seem that the same issue was happening with the wishlist.
See first release note for 2.3.1

I assume this could be fixed in the same way. Looking for the commit that fixed that. For some reason there is no link in the release notes.

[hostep]

@drew7721: just a hint, if you look in the source code of the release notes, you'll find the ticket number: MAGETWO-95311. If you then search for commits in a clone of this git repo using something like: git log origin/2.4-develop --grep 'MAGETWO-95311', you'll find 2 commits:

• 4333c92bf37af3c9e50fd953a46e904f0a1c2b05 (the fix)
• 6b14118933380d3d80d2efcb9a3e6095a93cb6b1 (the merge commit)

Not sure if this will be helpful here, but now you learned how to find fixes from the release notes in the git repository 🙂

[drew7721]

Great hint @hostep ! That will be very handy! Thanks!

[KonstantinZhidkovskiy]

@magento I’m working on it

[KonstantinZhidkovskiy]

@magento I am working on this