HIBERNATE,JPA Object Association Mapping

The correlation mapping is a complex mapping relationship in the mapping relationship, which has a pair of more than one or one pairs and many pairs of relationships. They are subdivided into one-way and two-way points. Let's introduce each of the following.

One-way Onetoone

One-way one-to-one is the simplest of the relational mappings, simply that you can query the other party from the associated side, but not the reverse. We use the example below to illustrate that the person entity class in Listing 1 and the address class in Listing 2 are one-way one-to-one relationships where we can query the contents of a person's corresponding address, but we cannot Value to query for the person who corresponds to this value.

Listing 1. Owning side of one-way one-to-one relationship

@Entity public class Person implements Serializable {private static final long serialversionuid = 1L; @Id @GeneratedValue ( Strategy = Generationtype.auto) private Long ID; Private String http://www.aliyun.com/zixun/aggregation/11696.html ">name; private int age; @OneToOne private address address; Getters & Setters}

Listing 2. The opposite end of one-way one-to-one relationship

@Entity public class address implements Serializable {private static final long serialversionuid = 1L; @Id @GeneratedValue ( Strategy = Generationtype.auto) private Long ID; Private String Street; Private String City; Private String country; gettes& Setters}

Figure 1. ER diagram of one-way one-to-one relationship

As you can see from their ER diagram in Figure 1, this one-way one-to-one relationship is mapped in the database as a form of a key outside of the bond. Where the sender of the relationship stores a foreign key that points to the receiving end of the relationship. In this example, the address_id in the person table is a foreign key that points to the address, and by default the field name of the foreign key is made up of the name of the table to which it points "_" Plus "ID". Of course, we can also modify the field according to our preferences, the modified method is to use @JoinColumn this annotation. In this example we can add this annotation to the address attribute in the person class.