Managing entities - EJB 3 in Action - page 404

a many-to-one relationship with the Seller entity (a seller can sell more than one item,
but an item can be sold by only one seller), a one-to-many relationship with the Bid en-
tity (more than one bid can be put on an item), and a many-to-many relationship with the
Category entity (an item can belong to more than one category and a category contains
multiple items). These relationships are depicted in figure 10.7 .
Figure 10.7. The Item entity is related to three other entities: Seller, Bid, and Category. The relationships
to Item are many-to-one, one-to-many, and many-to-many, respectively.
When the find method returns an instance of an Item , it also automatically retrieves the
Seller , Bid , and Category entities associated with the instance and populates them
into their respective Item entity properties. As shown in listing 10.5 , the single Seller
entity associated with the Item is populated into the seller property, the Bid entities
associated with an Item are populated into the bids list, and the Category entities the
Item is listed under are populated into the categories property. It might surprise you
to know some of these relationships are retrieved lazily.
All the relationship annotations you saw in chapter 9 , including the @ManyToOne ,
@OneToMany , and @ManyToMany annotations, have a fetch element to control fetch
modes, just like the @Basic annotation discussed in the previous section. None of the re-
lationship annotations in the following listing specify the fetch element, so the default
for each annotation takes effect.