休眠中的外键

Question

我有两个简单的表Customers和Orders，oneToMany到customer表的关系为Orders。

这是我的Customers.java

@Entity
public class Customers implements Serializable {

@Id
@GeneratedValue
private int cID;
private String name;
private String email;

// getter and setters
}

这是Orders.java：

@Entity
public class Orders implements Serializable {

@Id
@GeneratedValue
private int orderID;
private int cId;
@Column(nullable = false)
@Temporal(TemporalType.DATE)
private Date date;

@ManyToOne(cascade = CascadeType.ALL)
private Customers customers;
// getter and setters
}

现在，我要在Orders表中插入两条记录：

    public static void main(String[] args) {
    SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
    Session session = sessionFactory.openSession();
    session.beginTransaction();

    Orders orders1 = new Orders();
    Orders orders2 = new Orders();
    Customers customer = new Customers();
    customer.setName("c1");
    customer.setEmail("abc@gmail.com");

    orders1.setDate(new Date());
    orders2.setDate(new Date());

    orders1.setCustomers(customer);
    orders2.setCustomers(customer);

    session.save(orders1);
    session.save(orders2);

    session.getTransaction().commit();
    session.close();
    sessionFactory.close();
}

这是控制台中的结果：

Hibernate: alter table Orders drop foreign key FK_hmbx2rg9tsgqikb3kodqp90c4
Hibernate: drop table if exists Customers
Hibernate: drop table if exists Orders
Hibernate: create table Customers (cID integer not null auto_increment, email varchar(255), name varchar(255), primary key (cID))
Hibernate: create table Orders (orderID integer not null auto_increment, cId integer not null, date date not null, customers_cID integer, primary key (orderID))
Hibernate: alter table Orders add constraint FK_hmbx2rg9tsgqikb3kodqp90c4 foreign key (customers_cID) references Customers (cID)
Feb 24, 2015 1:58:52 PM org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: insert into Customers (email, name) values (?, ?)
Hibernate: insert into Orders (cId, customers_cID, date) values (?, ?, ?)
Hibernate: insert into Orders (cId, customers_cID, date) values (?, ?, ?)

这是结果表：

为什么cID表中的Orders（这是customers的外键引用）是0？

应为1。

Answer 1

它认为orders表customers_cId是customers表的实际外键引用列。由于您没有明确地给出任何列名，因此通过连接两个实体的变量，内部将列名称作为customers_cId。来自customers实体的orders和cId的{​​{1}}。

只是为了验证您可以尝试使用customers注释提供其他名称。

@JoinColumn

@ManyToOne(cascade = CascadeType.ALL) @JoinColumn(name="order_cId") private Customers customers; 表中的cId只是一个独立的列，因为您没有为其设置任何值，它将默认值设为orders。尝试为其设置一些随机值。