Problem with persisting property of type java.lang.Class

s.goetz · **Posted:** Mon Jan 28, 2013 9:34 am

Dear board users,

I face a strange problem with my entity class. Let me try to explain what I intend to do:

I have a hierarchical structure of hardware components that I persist in a database using

Code:

@Inheritance(strategy = InheritanceType.JOINED)

For these components there is a concept named 'resourcing' which means that each hardware component may have an owner and children. You do not need to full yunderstand that to understand the problem. For this mapping I have build an entity called Resource.

Code:

@Entity
// Keep resourceNumber unique for each controller and resourceType
@Table(name = "ResourceMap", uniqueConstraints = { @UniqueConstraint(columnNames = { "resourceType", "resourceNumber", "ownerId" }) })
@Audited
@Indexed
public class Resource extends BaseEntity
{
    public static final String PROPERTY_RESOURCE_TYPE = "resourceType";
    public static final String PROPERTY_RESOURCE_LOCATION = "resourceLocation";
    public static final String PROPERTY_RESOURCE_NUMBER = "resourceNumber";
    public static final String PROPERTY_OWNER = "owner";
    public static final String PROPERTY_ENTITY_CLASS = "entityClass";
    public static final String PROPERTY_ENTITY_ID = "entityId";
    public static final String PROPERTY_CONTROLLER = "controller";
    public static final String PROPERTY_CHILDREN = "children";

    @Column(name = PROPERTY_RESOURCE_TYPE, nullable = false)
    @NotNull
    @Enumerated(EnumType.ORDINAL)
    @Viewable
    private ResourceType resourceType;

    @Column(name = PROPERTY_RESOURCE_LOCATION, nullable = false)
    @NotNull
    @Enumerated(EnumType.ORDINAL)
    @Viewable
    private ResourceLocation resourceLocation = ResourceLocation.CONTROLLER;

    @Column(name = PROPERTY_RESOURCE_NUMBER, nullable = false)
    @NotNull
    @Viewable
    private Short resourceNumber = 0;

    @JoinColumn(name = "ownerId", nullable = false)
    @ManyToOne(fetch = FetchType.LAZY)
    @IndexedEmbedded(depth = 1)
    @NotNull
    private Resource owner;

    @Column(name = PROPERTY_ENTITY_CLASS)
    // @NotNull
    private Class<  entityClass;

    @Column(name = PROPERTY_ENTITY_ID)
    @NotNull
    private String entityId;

    @JoinColumn(name = "controllerId", nullable = false)
    @ManyToOne(fetch = FetchType.LAZY)
    @IndexedEmbedded(depth = 1)
    @NotNull
    private Controller controller;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = PROPERTY_OWNER, cascade = CascadeType.ALL, orphanRemoval = true)
    private final Set<Resource> children = new HashSet<>();

    // getters and setters
}

As you can see I persist the mapped entity's java class and unique id. I can do that as I like and have the correct values in the database e.g.:

Code:

id                                   version  entityClass       entityId                             resourceLocation resourceNumber resourceType controllerId                          ownerId                              
949ff828-8cbd-4f81-ba88-07a433fa1250 0        foo.bar.className e923f95f-1266-4690-98c2-68cbfbbcb530 0                0               8            e923f95f-1266-4690-98c2-68cbfbbcb530 949ff828-8cbd-4f81-ba88-07a433fa1250

Now the problem is when I try to read this line using hibernate's criteria API I get a strange SQLGrammarException:

Quote:

Conversion failed when converting the nvarchar value 'foo.bar.className' to data type int

The criteria I am building is quite simple:

Code:

Criteria query = getSession().createCriteria(Resource.class);

query.add(Restrictions.eq(Resource.PROPERTY_ENTITY_CLASS, foo.bar.className.class));
query.add(Restrictions.eq(Resource.PROPERTY_ENTITY_ID, "e923f95f-1266-4690-98c2-68cbfbbcb530"));

return (Resource) query.uniqueResult();

The problem seems to be that the class "foo.bar.className" is itself a persisted entity class. So hibernate trys for some reason to determine a discriminator of type int and maps it to the "entityClass" column. The code for that is located at org.hibernate.loader.criteria.CriteriaQueryTranslator.getTypedValue(Criteria, String, Object).
I have tested it with other classes that are themselves no persisted entities and for these it works as expected.

So the actual question is: How can I prevent that hibernate resolves thios discriminator value?

EDIT:
I found somethingout myself. When using the restriction as native SQL-restriction it works:

Code:

Criteria query = getSession().createCriteria(Resource.class);

query.add(Restrictions.sqlRestriction("{alias}." + Resource.PROPERTY_ENTITY_CLASS + " = ?", foo.bar.className.class, ClassType.INSTANCE));
// query.add(Restrictions.eq(Resource.PROPERTY_ENTITY_CLASS, foo.bar.className.class));
query.add(Restrictions.eq(Resource.PROPERTY_ENTITY_ID, "e923f95f-1266-4690-98c2-68cbfbbcb530"));

return (Resource) query.uniqueResult();