Serialization incomplete on JOINED inheritance subclass

[antoinenedelecdecathlon]

API Platform version(s) affected: 3.1.22

Description

I am serializing an object of class foo :

• GET operation on /foos/1
• fooGroup normalization context group

My foo class have two ManyToOne attributes:

• barSingleTable (a class with SINGLE_TABLE InheritanceType)
  • this class contain a x attribute, with the fooGroup for normalization
• barJoined (a class with JOINED InheritanceType)
  • the main table have two joined entities barJoinedA and barJoinedB
  • both have a respective attribute Y and Zcontaining the fooGroup for normalization

When I fetch /foos/1, here is my payload:

{
    "@context": "/api/contexts/Foo",
    "@id": "/api/foos/1",
    "@type": "Foo",
    "bar_single_table": {
        "@id": "/api/bar_single_tables/1",
        "@type": "BarSingleTable",
        "x": "x_value"
    },
    "bar_joined": "/api/bar_joined_a/1"
}

Here is what I expect:

{
    "@context": "/api/contexts/Foo",
    "@id": "/api/foos/1",
    "@type": "Foo",
    "bar_single_table": {
        "@id": "/api/bar_single_tables/1",
        "@type": "BarSingleTable",
        "x": "x_value"
    },
    "bar_joined": {
        "@id": "/api/bar_joined_a/1",
        "@type": "BarJoinedA",
        "y": "y_value"
    }
}

NB: IF I add the fooGroup group on ANY attribute of the main joined class (let's say the $id), everything works well as intended, and all joined attribute are now serialized :

{
    "@context": "/api/contexts/Foo",
    "@id": "/api/foos/1",
    "@type": "Foo",
    "bar_single_table": {
        "@id": "/api/bar_single_tables/1",
        "@type": "BarSingleTable",
        "x": "x_value"
    },
    "bar_joined": {
        "@id": "/api/bar_joined_a/1",
        "@type": "BarJoinedA",
        "y": "y_value",
        "id": 1
    }
}

Possible Solution
I would think the check for serialization isn't done on the joined entities, but if this check is passed the serialization process is OK.

UPDATE 26/03:

the ApiProperty in SerializerPropertyMetadataFactory->transformLinkStatus function has a builtIn type of the parent DiscriminatorMap class. So I guess this is "logical" that the getClassSerializerGroups does not return all the possible child class groups.

How would a MetadataFactory instanciate an ApiProperty with the correct requested child Discriminator class ?