Re: hibernate mapping pro

Hi folks,

I have a problem using Hibernate Annotations. I try to map the
following entity relation_

ER-Diagram:

+------+ 1 * +-------------------+ * 1 +------+
|ClassA| ------<>----- |ClassAClassBMapping| -----<>----- |ClassB|
+------+ +-------------------+ +------+

Intention:
a unidirectional mapping of ClassB to ClassA without a special entity
for ClassAClassBMapping

The following Scenario is working:

Enum MyEnum{
    A,B,C
}

@Entity (name="entity_a")
@Table(name="table_a")
class ClassA {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany(targetEntity = ClassB.class)
    @MapKey(name = "classb_id")
    @JoinTable(name = "ClassAClassBMapping", joinColumns =
@JoinColumn(columnDefinition = "classa_id", table = "table_a", name =
"id", nullable = false),
            inverseJoinColumns = @JoinColumn(columnDefinition =
"classb_id", table = "table_b", name = "id", nullable = false),
            uniqueConstraints = @UniqueConstraint(columnNames = {
            "classa_id", "classb_id"
    }))
    private Map<MyEnum,ClassB> bClasses;
}

@Entity (name="entity_b")
@Table(name="table_b")
ClassB {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Embedded
    private MyEnum myEnum;
}

The trouble with this solution is the point, that the enumeration is
not a property of ClassB but classification of ClassB in ClassA. As I
use the enumeration as a property I will get lots of redundant
datasets, that slowdown the application and make it difficult to
handle modifications.

My favored solution is shown below but that solution doesn't work.

Entities:

@Embeddable
Enum MyEnum{
    A,B,C
}

@Entity (name="entity_a")
@Table(name="table_a")
class ClassA {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToMany(targetEntity = ClassB.class)
    @MapKey(name = "myEnum")
    @JoinTable(name = "ClassAClassBMapping", joinColumns =
@JoinColumn(columnDefinition = "classa_id", table = "table_a", name =
"id", nullable = false),
            inverseJoinColumns = @JoinColumn(columnDefinition =
"classb_id", table = "table_b", name = "id", nullable = false),
            uniqueConstraints = @UniqueConstraint(columnNames = {
            "classa_id", "myEnum"
    }))
    private Map<MyEnum,ClassB> bClasses;
}

@Entity (name="entity_b")
@Table(name="table_b")
ClassB {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
}

I cannot deliver an errormessage, because spring-framework only
reports that the sessionfactory cannot be instantiated. As soon as I
remove the mapping or change the mapping to the first example all
JUnit-tests work fine. So I am sure that the configuration of spring
is ok.

Any idea's what is the problem?

Kind Regards
Mark