[Issue] Fix error visiting compare page without items

[m2-assistant]

This issue is automatically created based on existing pull request: #40203: Fix error visiting compare page without items

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Description (*)

Going incognito and visiting /catalog/product_compare/index/ will cause an

Item (Magento\Catalog\Model\Product\Interceptor) with the same ID "xxx" already exists.

Error on many live webshops. This is because the database table looks somewhat like this

catalog_compare_item_id	visitor_id	customer_id	product_id	store_id	list_id
23159	4690502		19028	1
22917	0		18906	1	711
23034	0		18868	1	732
22916	0		18851	1	711
21991	0		18783	1	537
21573	0		18747	1	451
22196	0		18740	1	585
22485	0		18706	1	644
22111	0		18705	1	568
22259	0		18689	1	596
22133	0		18689	1	573
21802	0		18689	1	492

Thus if we only get items with visitor_id 0 and customer_id NULL we will get duplicate products (and compare product from other customers...)

Manual testing scenarios (*)

1. Ensure your catalog_compare_items somewhat matches the example above (duplicate product id's on different lists)
2. Visit the /catalog/product_compare/index/ route in incognito, so no visitor id, customer id, or list id is assigned to you
3. See the error that occurs.

Additional Steps

It'd be quite simple to trigger this behavior using graphql:

curl 'https://magento.test/graphql' \
  -H 'accept: application/json' \
  -H 'content-type: application/json' \
  --data-raw '{"query":"mutation createCompareList($input: CreateCompareListInput) {\n  createCompareList(input: $input) {\n    item_count\n    uid\n  }\n}","variables":{"input":{"products":[23]}},"operationName":"createCompareList"}'

Call this query a couple of times (to emulate multiple users adding this product to their compare list), navigate to the /catalog/product_compare/index/ page and you should get this error.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[engcom-Hotel]

Hello @indykoning,

Thanks for the report and collaboration!

We have tried to reproduce the issue with the mentioned scenario where list_id contains the data with duplicate product ids but the same has been not occured for us.

Can you please help us with getting the same by sharing any screencast or screenshot?

Thanks

[indykoning]

Using the Sample Magento installation and this mysql dump preparing the catalog_compare_item and catalog_compare_list tables you should be able to reproduce the issue

magento-product_compare_setup.sql

Exception #0 (Exception): Item (Magento\Catalog\Model\Product\Interceptor) with the same ID "23" already exists.
#1 Magento\Eav\Model\Entity\Collection\AbstractCollection->addItem() called at [vendor/magento/module-eav/Model/Entity/Collection/AbstractCollection.php:1167]
#2 Magento\Eav\Model\Entity\Collection\AbstractCollection->_loadEntities() called at [vendor/magento/module-eav/Model/Entity/Collection/AbstractCollection.php:955]
#3 Magento\Eav\Model\Entity\Collection\AbstractCollection->load() called at [vendor/magento/module-catalog/Model/ResourceModel/Product/Collection.php:835]
#4 Magento\Catalog\Model\ResourceModel\Product\Collection->load() called at [vendor/magento/framework/Interception/Interceptor.php:58]
#5 Magento\Catalog\Model\ResourceModel\Product\Compare\Item\Collection\Interceptor->___callParent() called at [vendor/magento/framework/Interception/Interceptor.php:138]
#6 Magento\Catalog\Model\ResourceModel\Product\Compare\Item\Collection\Interceptor->Magento\Framework\Interception\{closure}() called at [vendor/magento/framework/Interception/Interceptor.php:153]
#7 Magento\Catalog\Model\ResourceModel\Product\Compare\Item\Collection\Interceptor->___callPlugins() called at [generated/code/Magento/Catalog/Model/ResourceModel/Product/Compare/Item/Collection/Interceptor.php:23]
#8 Magento\Catalog\Model\ResourceModel\Product\Compare\Item\Collection\Interceptor->load() called at [vendor/magento/framework/Data/Collection.php:847]
#9 Magento\Framework\Data\Collection->getIterator() called at [vendor/magento/module-catalog/view/frontend/templates/product/compare/list.phtml:30]

As an example of the "Data leak" i've resolved the duplicate products on different lists and without having added any products myself, this is the compare page:

[engcom-Hotel]

Thank you @indykoning for further steps to reproduce the issue.

After manipulating data into database table, the issue is reproducible now. But we are looking for the steps so that the issue can be reproduce either from frontend or API/GraphQL.

Please let us know the same.

[indykoning]

It'd be quite simple to trigger this behavior using graphql:

curl 'https://magento.test/graphql' \
  -H 'accept: application/json' \
  -H 'content-type: application/json' \
  --data-raw '{"query":"mutation createCompareList($input: CreateCompareListInput) {\n  createCompareList(input: $input) {\n    item_count\n    uid\n  }\n}","variables":{"input":{"products":[23]}},"operationName":"createCompareList"}'

Call this query a couple of times (to emulate multiple users adding this product to their compare list), navigate to the /catalog/product_compare/index/ page and you should get this error.

[engcom-Hotel]

Thank You @indykoning for the additional information.

The issue is now reproducible for us. Hence confirming the issue.