Java Hibernate中@MapsId注释的用途
我试图理解@MapsId注释在Hibernate中的区别。我已经阅读了Hibernate文档,但是我仍然对其中给出的解释感到困惑,因为我对Hibernate还不熟悉 报告说:Java Hibernate中@MapsId注释的用途,java,hibernate,Java,Hibernate,我试图理解@MapsId注释在Hibernate中的区别。我已经阅读了Hibernate文档,但是我仍然对其中给出的解释感到困惑,因为我对Hibernate还不熟悉 报告说: @Entity class Customer { @EmbeddedId CustomerId id; boolean preferredCustomer; @MapsId("userId") @JoinColumns({ @JoinColumn(name="userfirstname
@Entity
class Customer {
@EmbeddedId CustomerId id;
boolean preferredCustomer;
@MapsId("userId")
@JoinColumns({
@JoinColumn(name="userfirstname_fk", referencedColumnName="firstName"),
@JoinColumn(name="userlastname_fk", referencedColumnName="lastName")
})
@OneToOne User user;
}
@Embeddable
class CustomerId implements Serializable {
UserId userId;
String customerNumber;
//implements equals and hashCode
}
@Entity
class User {
@EmbeddedId UserId id;
Integer age;
}
@Embeddable
class UserId implements Serializable {
String firstName;
String lastName;
//implements equals and hashCode
}
在嵌入式id对象中,关联表示为
关联实体的标识符。但您可以将其值链接到
通过@MapsId注释在实体中进行常规关联。这个
@MapsId值对应于嵌入id的属性名称
对象,该对象包含关联实体的标识符。在数据库中,
这意味着Customer.user和CustomerId.userId属性
共享相同的基础列(本例中为用户_fk)
我不清楚这个解释是怎么说的,所以我厌倦了在我的配置文件中将hbm2ddl
设置为create
,我观察到:
对于客户实体上的@MapsId和@JoinColumns,DDL语句为:
Hibernate: create table CUSTOMER (customerNumber varchar2(255 char) not null, preferredCustomer number(1,0) not null, userfirstname_fk varchar2(255 char) not null, userlastname_fk varchar2(255 char) not null, primary key (customerNumber, userfirstname_fk, userlastname_fk))
Hibernate: create table USER (firstName varchar2(255 char) not null, lastName varchar2(255 char) not null, age number(10,0), primary key (firstName, lastName))
Hibernate: alter table CUSTOMER add constraint UK_xxxx unique (userfirstname_fk, userlastname_fk)
Hibernate: alter table CUSTOMER add constraint FK_xxxx foreign key (userfirstname_fk, userlastname_fk) references TBL_USER
如果删除@MapsId和@JoinColumns注释,我会看到以下内容:
Hibernate: create table CUSTOMER (customerNumber varchar2(255 char) not null, firstName varchar2(255 char), lastName varchar2(255 char), preferredCustomer number(1,0) not null, user_firstName varchar2(255 char), user_lastName varchar2(255 char), primary key (customerNumber, firstName, lastName))
Hibernate: create table USER (firstName varchar2(255 char) not null, lastName varchar2(255 char) not null, age number(10,0), primary key (firstName, lastName))
Hibernate: alter table CUSTOMER add constraint FK_xxxx foreign key (user_firstName, user_lastName) references TBL_USER
请帮助我理解Hibernate中@MapsId注释的概念。@MapsId将主实体的主键作为子实体的主键共享,无需在子实体中插入外键。Hibernate将映射两个实体的PK并向我们返回一个对象。谢谢Kanagaraj,您能告诉我哪一个被认为是主实体,哪一个是子实体吗?在您的情况下,客户是主实体,用户是子实体。