Indices from sub classes always get re-created

[buffcode]

Bug Report

Q	A
BC Break	no
Version	2.5.3

Summary

Having an inheritance and defining indices on a subclass (eg. UniqueIndex) will always re-create the subclasses' indices.

Current behavior

Having an inheritance and defining indices on a subclass (eg. UniqueIndex) will result in the subclass indices to be dropped on every run of doctrine:mongodb:schema:update and re-created afterwards.

Notice that the index will exist after the command, so the collection looks okay, but the indices are effectively dropped and recreated.
This is usually not such of a big problem but it put some our our databases down after dropping an index on a 0,5 TB collection and starting to recreate it for multiple hours.

How to reproduce

<?php

use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;

/**
 * @ODM\Document()
 * @ODM\InheritanceType("SINGLE_COLLECTION")
 * @ODM\DiscriminatorField("metadataType")
 */
abstract class Metadata
{
    /**
     * @ODM\Id()
     */
    protected ?string $id = null;

    public function getId(): ?string
    {
        return $this->id;
    }
}

<?php

use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;

/**
 * @ODM\Document()
 */
class PreAggregationMetadata extends Metadata
{
    /**
     * @ODM\UniqueIndex()
     * @ODM\Field(type="string")
     */
    private string $cacheKey;
}

For debugging purposes add the following code to \Doctrine\ODM\MongoDB\SchemaManager::updateDocumentIndexes, right before $collection->dropIndex(...):

dump('Dropping index ' . $mongoIndex['name'] . ' on ' . $documentName);

Run:

$ bin/console doctrine:mongodb:schema:update
Dropping index cacheKey on Metadata
Updated indexes for all classes
Updated validation for all classes

Expected behavior

No index drop

$ bin/console doctrine:mongodb:schema:update
Updated indexes for all classes
Updated validation for all classes

Workaround

All indices have to be defined on the root class.

[malarzm]

@buffcode thanks for the report! Would the same be true if Metadata was mapped as a ODM\MappedSuperclass instead of ODM\Document? That would be more correct from a configuration's point of view as Metadata can not be a document on its own

[buffcode]

@malarzm The effect seems to be the same. Having the parent being abstract without MappedSuperclass is used to be able to query all subclasses ("A mapped superclass cannot be a document and is not queryable."), while ODM automatically returns the correct type.

Nevertheless, while testing various combinations of abstract and MappedSuperclass I also had following error, resulting in no index at the end, presumably because the order of the index creation is not correct:

<?php

use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;

/**
 * @ODM\Document()
 * @ODM\InheritanceType("SINGLE_COLLECTION")
 * @ODM\DiscriminatorField("metadataType")
 */
class ClassA
{
    /**
     * @ODM\Id()
     */
    protected ?string $id = null;
}

<?php

use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;

/**
 * @ODM\Document()
 */
class ClassB extends ClassA
{
    /**
     * @ODM\Index()
     */
    protected ?string $foo = null;
}

Output:

$ console dev:doctrine:mongodb:schema:update -vv 2>&1 | grep 'Class'
07:28:02 INFO      [app] [MongoDB] Creating index on ClassA: foo_1
07:28:02 WARNING   [app] [MongoDB] Dropping index on ClassA: foo_1

Database view:

---

IMHO the index comparison needs to take all subclasses into account and perform the index deletion/creation only once per collection. The subclasses can be skipped, as they have already been processed by the parent.

[malarzm]

Thanks for checking! You're right, we'll need to improve how indices are created. Most probably in the same vein as #2392 did. Mind taking a stab at it? :)