Question:
Can you give me an example of a Hibernate mapping for the following situation:
- Parent table(
foo) with a simple primary key (foo_id) -
child table(
bar) with a composite key consisting ofa) Foreign key to parent table (
foo_id)b) key(
item) of type string - There is one parent to many child
- The Parent class will have a list of Child objects
- When a Parent class is saved, updated, deleted the changes will cascade to the Child
Solution:1
I haven't done exactly what you are asking for but this might start you off in the right direction. I think it should work. This page explains these annotations in greater detail.
@Entity public class Foo { @Id @GeneratedValue(strategy=GenerationType.AUTO) public Long getId(){ } ... @OneToMany(mappedBy="foo") public Collection<Bar> getBars() { } ... } @Entity @IdClass(BarPk.class) public class Bar implements Serializable { @ManyToOne @JoinColumn(name="foo") @Id public Foo getFoo() { return foo; } @Column(name="key", length=255) @Id public String getKey(){ } } @Embeddable public class BarPk implements Serializable { public Foo getFoo() { return foo; } public void setFoo(Foo foo) { } public String getKey(){ ... } public void setKey(String key){ ... } //you must include equals() and hashcode() }
Solution:2
Yes, you should use the following mapping
@Entity public class Parent {
@Id private Integer id; @CollectionOfElements @JoinTable( name="Child", joinColumn=@JoinColumn(name="PARENT_ID")) @IndexColumn("childIndex") private List<Child> childList = new ArrayList<Child>(); }
Notice @CollectionOfElements and IndexColumn is Hibernate specific annotations, not JPA 1.0 specification. JPA 2.0 will introduce them.
@Embeddable public class Child {
// @Embeddable class does not contains identifiers // child class specific property's }
So the following code will works fine
Parent parent = new Parent();
parent.getChildList().add(new Child()); parent.getChildList().add(new Child()); // other child
session.save(parent); // A parent and two children will be saved
The drawback with this issue is that @CollectionOfElements annotation only applies to @Embeddadble class, not a Entity class. If you want a Child class as a Entity class, i would like to see the solution. It is not possible applies at the same time @Entity and @Embeddable annotations to a class.
Regards Arthur Ronald F D Garcia (Java programmer) Natal/RN - Brazil
Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
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