Hiberate 多对多映射注解示例
原文： https://howtodoinjava.com/hibernate/hibernate-many-to-many-mapping-using-annotations/
在两个实体之间建立多对多 Hiberate 的映射，其中一个实体可以与多个其他实体实例相关。 例如，对于订阅服务，SubscriptionEntity和ReaderEntity可以是两种类型的实体。 任何订阅都可以有多个阅读器，其中一个阅读器可以订阅多个订阅。
在此 hibernate 教程中，我们将学习使用 hibernate 在数据库中创建多对多映射。
Table of contents
Hibernate many to many mapping design
Owner entity
Mapped entity
Configure entities in hibernate config file
Demo
1. Hiberate 多对多映射设计
为了演示使用 Hiberate 注解的多对多映射，我们将关联两个实体，即ReaderEntity和SubscriptionEntity。
他们的数据库架构应如下所示。 使用这些表，任何应用都可以保存读者和订阅之间的多个关联。
2. 所有者实体
所有者实体是负责建立关联并维护它的实体。 在我们的情况下，我将ReaderEntity设置为所有者实体。 @JoinTable注解已用于建立此关联。
package hibernate.test.manyToMany.joinTable;
import java.io.Serializable;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;
@Entity(name = "ReaderEntity")
@Table(name = "READER", uniqueConstraints = {
@UniqueConstraint(columnNames = "ID"),
@UniqueConstraint(columnNames = "EMAIL") })
public class ReaderEntity implements Serializable
{
private static final long serialVersionUID = -1798070786993154676L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID", unique = true, nullable = false)
private Integer readerId;
@Column(name = "EMAIL", unique = true, nullable = false, length = 100)
private String email;
@Column(name = "FIRST_NAME", unique = false, nullable = false, length = 100)
private String firstName;
@Column(name = "LAST_NAME", unique = false, nullable = false, length = 100)
private String lastName;
@ManyToMany(cascade=CascadeType.ALL)
@JoinTable(name="READER_SUBSCRIPTIONS", joinColumns={@JoinColumn(referencedColumnName="ID")}
, inverseJoinColumns={@JoinColumn(referencedColumnName="ID")})
private Set<SubscriptionEntity> subscriptions;
//Getters and setters
}
3. 映射实体
我们的映射实体是SubscriptionEntity，它使用“mappingBy”属性映射到ReaderEntity。
package hibernate.test.manyToMany.joinTable;
import java.io.Serializable;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;
@Entity(name = "SubscriptionEntity")
@Table(name = "SUBSCRIPTION", uniqueConstraints = {
@UniqueConstraint(columnNames = "ID")})
public class SubscriptionEntity implements Serializable
{
private static final long serialVersionUID = -6790693372846798580L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID", unique = true, nullable = false)
private Integer subscriptionId;
@Column(name = "SUBS_NAME", unique = true, nullable = false, length = 100)
private String subscriptionName;
@ManyToMany(mappedBy="subscriptions")
private Set<ReaderEntity> readers;
//Getters and setters
}
4. 在 Hiberate 配置文件中配置实体
我们使两个实体都可以在运行时使用。 为此，我们必须将它们添加到hibernate.cfg.xml文件中。
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernatetest</property>
<property name="hibernate.connection.password">XXXXXX</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">create</property>
<mapping class="hibernate.test.manyToMany.joinTable.ReaderEntity"/>
<mapping class="hibernate.test.manyToMany.joinTable.SubscriptionEntity"/>
</session-factory>
</hibernate-configuration>
5. Hiberate 多对多注解映射示例
现在，该测试代码了。 我编写了以下代码来测试上述实体及其多对多关系。
package hibernate.test.manyToMany;
import hibernate.test.HibernateUtil;
import hibernate.test.manyToMany.joinTable.*;
import java.util.HashSet;
import java.util.Set;
import org.hibernate.Session;
public class TestJoinTable
{
public static void main(String[] args)
{
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
//Add subscription
SubscriptionEntity subOne = new SubscriptionEntity();
subOne.setSubscriptionName("Entertainment");
SubscriptionEntity subTwo = new SubscriptionEntity();
subTwo.setSubscriptionName("Horror");
Set<SubscriptionEntity> subs = new HashSet<SubscriptionEntity>();
subs.add(subOne);
subs.add(subTwo);
//Add readers
ReaderEntity readerOne = new ReaderEntity();
readerOne.setEmail("demo-user1@mail.com");
readerOne.setFirstName("demo");
readerOne.setLastName("user");
ReaderEntity readerTwo = new ReaderEntity();
readerTwo.setEmail("demo-user2@mail.com");
readerTwo.setFirstName("demo");
readerTwo.setLastName("user");
Set<ReaderEntity> readers = new HashSet<ReaderEntity>();
readers.add(readerOne);
readers.add(readerTwo);
readerOne.setSubscriptions(subs);
readerTwo.setSubscriptions(subs);
session.save(readerOne);
session.save(readerTwo);
session.getTransaction().commit();
HibernateUtil.shutdown();
}
}
程序输出：
Hibernate: insert into READER (EMAIL, FIRST_NAME, LAST_NAME) values (?, ?, ?)
Hibernate: insert into SUBSCRIPTION (SUBS_NAME) values (?)
Hibernate: insert into SUBSCRIPTION (SUBS_NAME) values (?)
Hibernate: insert into READER (EMAIL, FIRST_NAME, LAST_NAME) values (?, ?, ?)
Hibernate: insert into READER_SUBSCRIPTIONS (readers_ID, subscriptions_ID) values (?, ?)
Hibernate: insert into READER_SUBSCRIPTIONS (readers_ID, subscriptions_ID) values (?, ?)
Hibernate: insert into READER_SUBSCRIPTIONS (readers_ID, subscriptions_ID) values (?, ?)
Hibernate: insert into READER_SUBSCRIPTIONS (readers_ID, subscriptions_ID) values (?, ?)
在此示例中，我们了解了在 Hiberate 中使用多对多注解来连接表。
学习愉快！