Feature: #98132 - Extbase entity properties support union types

See forge#98132

Description

Extbase's reflection does now support the detection of union types in entity properties.

Before, whenever a union type was needed, union type declarations led to Extbase not detecting any type at all, resulting in the property not being mapped. Union types could be resolved via doc blocks however:

class Entity extends AbstractEntity
{
    /**
     * @var ChildEntity|LazyLoadingProxy
     */
    private $property;
}

Now, this is possible:

class Entity extends AbstractEntity
{
    private ChildEntity|LazyLoadingProxy $property;
}

This is especially useful for lazy loaded relations where the property type is LazyLoadingProxy|ChildEntity.

There is something important to understand about how Extbase detects unions when it comes to property mapping, i.e. when a database row is mapped onto an object. In this case, Extbase needs to know the desired target type. No union, no intersection, just one type. In order to achieve this, Extbase uses the first declared type as a so called primary type.

class Entity extends AbstractEntity
{
    private string|int $property;
}

In this case, string is the primary type. int|string would result in int as primary type.

There is one important thing to note and one exception to this rule. First of all, null is not considered a type. null|string results in primary type string, which is nullable. null|string|int also results in primary type string. In fact, null means that all other types are nullable. null|string|int boils down to ?string or ?int.

Secondly, LazyLoadingProxy is never detected as primary type because it's just a proxy and not the actually target type, once loaded.

class Entity extends AbstractEntity
{
    private LazyLoadingProxy|ChildEntity $property;
}

Extbase supports this and detects ChildEntity as primary type, although LazyLoadingProxy is first item in the list. However, it is recommended to place the actual type first, for consistency reasons: ChildEntity|LazyLoadingProxy.

A final word on LazyObjectStorage: LazyObjectStorage is a subclass of ObjectStorage, therefore the following code works and has always been working:

class Entity extends AbstractEntity
{
    /**
     * @var ObjectStorage<ChildEntity>
     * @TYPO3\CMS\Extbase\Annotation\ORM\Lazy
     */
    private ObjectStorage $property;
}

Impact

As described above, the main impact is Extbase being able to detect and support union type declarations for entity properties.