From: Markus Fuchs <Markus.Fuchs_at_Sun.COM>
Date: Fri, 03 Nov 2006 13:23:33 -0800

Hi Antonio,

According to the JPA spec, unidirectional OneToMany relationships should be mapped to a join table (see 2.1.8.5.1 Unidirectional OneToMany Relationships). The issue here is that the Collection side owns the relationship and is responsible for writing relationship updates to the database.

Unidirectional OneToMany relationships could be provided as vendor extension, and are not portable.

Only bi-directional relationships need a mappedBy annotation. The mappedBy annotation identifies the owning side. For a unidirectional relationship, there's only one side, therefore no need to identify an owning side.

-- markus.

Antonio Goncalves wrote:

Hoops, sorry. The first example without annotation (private List<OrderLine> orderLines) produces a jointable called Order_OrderLine. The question is more how to not have a join table but a foreign key in OrderLine ? 

2006/11/3, Antonio Goncalves <antonio.mailing@gmail.com>:

Hi.

 

I'm using GlassFish V2b24. I want to model a unidirectional OneToMany relationship between the two classes Order -----*-> OrderLine. A bi-directional relation works fine (addind a Order attribut into OrderLine), but I can't make the unidirectional work. Here is the code (simplified) :

 

public class Order implements Serializable {
    @Id @GeneratedValue
    private Long id;
    @ManyToOne @JoinColumn(name = "customer_fk", nullable = false)
    private Customer customer;
    private List<OrderLine> orderLines;
}

public class OrderLine implements Serializable {
    @Id @GeneratedValue
    private Long id;
    private Integer quantity;
    @OneToOne(optional = false) @JoinColumn(name = "item_fk")
    private Item item;
}

That works at deployment and creates both tables but without any foreign key or a join table between them. When I add the @OneToMany annotation :

    @OneToMany
    private List<OrderLine> orderLines;

It produces the following error at deployment :

org.apache.derby.client.am.SqlException: 'ORDER_FK' is not a column in table or VTI 'DBUSER.T_ORDER_LINE'.

And I would love to have a foreign key order_fk. I've also  read that for a unidirectional I need to use the mappedBy attribute. But this is what happens

@OneToMany(mappedBy = "order")
private List<OrderLine> orderLines;

Exception Description: The attribute [orderLines] in entity class [class com.yaps.petstore.entity.order.Order] has a mappedBy value of [order] which does not exist in its owning entity class [class com.yaps.petstore.entity.order.OrderLine ]. If the owning entity class is a @MappedSuperclass, this is invalid, and your attribute should reference the correct subclass.

What am I doing wrong ? Does anybody have an idea ?

Thanks,

Antonio