hibernate mapping problem

From:

"Mark Sudau" <mark.sudau@THRWHITE.remove-dii-this>

Newsgroups:

comp.lang.java.databases

Date:

Wed, 27 Apr 2011 15:23:21 GMT

Message-ID:

<49365f1d$0$30225$9b4e6d93@newsspool1.arcor-online.net>

  To: comp.lang.java.databases
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

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