@Embedded.Nullable returns as non-null for null collection property

[radekjezdik]

Given an @Embedded.Nullable on a property whose object contains a property with a collection type, e.g. list (backed by a varchar array in the DB), the annotated object is returned non-null even for a null value of this collection.

data class Entity(
    @Embedded.Nullable
    val embedded: EmbeddedObject?
) {
    @Id
    var id: Long? = null
}

data class EmbeddedObject(
    @Column("values")
    val values: List<String>?
)

For a row with values = null, the mapper results in the embedded property being a non-null object, and its property values is null.

I guess this is a bug, as it goes against the documented behavior:

the load strategy for the embedded object if all contained fields yield null values.

which should hold for an embedded with a single collection field yielding a null value.

version: 3.2.2

[mp911de]

Placing collections in an embeddable is somewhat problematic as the current code only checks values from the current row in ResultSet. To determine whether there are values, we would have to run a query to check whether there are values. Then run another query to fetch the actual rows. With a single property, all this can be done, but running multiple queries for multiple relationship properties is where it becomes problematic.

I agree this is a bug and we need to take care of it.

[radekjezdik]

Maybe I am lost in the context, but the collection is part of the current row when it is an array column. So, no additional query should be needed.

The code imho already has all the information needed to return the correct null result for the embedded object, as it needed to fill all the null fields in it already.

[mp911de]

You're right; I missed that the component type is String and, therefore, a simple type. In any case, we nee to fix the issue on our side.

[fantnk]

We also faced this problem. Do you have a workaround for that?

[Tree4Free]

After upgrading to 3.3.1 I encounter an issue that is probably related to this change:
Basically when fetching a list property it is returned as null when it is an empty list.

Using a combination of Java + Kotlin:
My Entity: (Java + Lombok)

@Data
@EqualsAndHashCode(callSuper = true)
@NoArgsConstructor
@AllArgsConstructor
public class MyTable extends Entity {
    List<String> tags;
}

My database table (postgres):

create table my_table
(
    id uuid not null,
    version bigint not null,
    tags text[] not null,
    constraint pk_my_table primary key (id)
);

My test case (Kotlin)

@Repository
interface MyTableRepository: CrudRepository<MyTable, UUID>, PagingAndSortingRepository<MyTable, UUID>

@Test
fun test() {
    val instance = myTableRepository.save(MyTable(null, 0, emptyList())) // instance.tags is still an empty list
    assertNotNull(myTableRepository.findById(instance.id).get().tags) // data from db tags is null
}

(I will create a seperate issue for this later this evening)