Many-To-Many :

There is a many-to-many relationship between org.jboss.tutorial.relationships.bean.Customer and org.jboss.tutorial.relationships.bean.Flight. In order to have a many-to-many relationship there needs to be a distinct join table that maps the many-to-many relationship. This is called an association table. You can have JBoss automatically generate the association table for you, or you can use the @JoinTable annotation to define it yourself. If you use @JoinTable it must be defined on both sides of the bi-directional relationship. Let's look at the Customer side of the relationship:

			 	
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER, mappedBy="customers")
			 	
			 

The mappedBy attribute states that the Flight.customers property is responsible for mapping and managing the relationship. The spec allows for multiple join and inverse join columns. See the "Composite Primary Key" tutorial for more information.

Let's look at the other side of the relationship in Flight.

				
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER)
@JoinTable(table = @Table(name = "flight_customer_table"),
                  joinColumns = {@JoinColumn(name = "FLIGHT_ID")},
                  inverseJoinColumns = {@JoinColumn(name = "CUSTOMER_ID")})
public Set<Customer> getCustomers()
{
   return customers;
}

				
			

The database associate table will look like this:

				
create table FLIGHT_CUSTOMER_TABLE (
      CUSTOMER_ID integer,
      FLIGHT_ID integer
   );