Eclipse + JBoss 5 + EJB3 Development Guide (9)

Implement Many-to-many (Many-to-many) mappings for entity beans

You need to use @manytomany to annotate fields or getter methods that encapsulate many-to-many relationships in EJB3. First look at the following table:

Figure 1 T_addresses Table

The T_addresses table and the T_customers table are many-to-many relationships. You need to use an association table to describe this relationship, and the structure of the associated table is shown in the following illustration.

Figure 2 T_customers_addresses

Define a Collection<address> Type field (addresses) in the customer class to hold multiple address objects corresponding to the Customer object, as follows:

Package entity;

Import java.util.Collection;

Import Javax.persistence.CascadeType;

Import javax.persistence.Entity;

Import Javax.persistence.FetchType;

Import Javax.persistence.GeneratedValue;

Import Javax.persistence.GenerationType;

Import Javax.persistence.Id;

Import Javax.persistence.JoinColumn;

Import javax.persistence.JoinTable;

Import Javax.persistence.ManyToMany;

Import Javax.persistence.OneToMany;

Import Javax.persistence.OneToOne;

Import Javax.persistence.PrimaryKeyJoinColumn;

Import javax.persistence.Table;

　　　 @Entity @Table (name = "T_customers") public class Customer {private int id;

　　　 private String name;

　　　 Private referee Referee;

　　　 Private collection<order> orders;

　　　 private collection<address> addresses; @ManyToMany (cascade = cascadetype.persist, fetch = Fetchtype.lazy) @JoinTable (name = "T_customers_addresses", Joincol Umns = @JoinColumn (name = "Customer_ID", referencedcolumnname = "id"), inversejoincolumns = @JoinColumn (name = "address_id", referencedcolumnname = "id")) public collection<address> getaddresses ()

　　　 {return addresses; } 　　　 ... ... }