# Hiberate 多对多映射注解示例 > 原文： [https://howtodoinjava.com/hibernate/hibernate-many-to-many-mapping-using-annotations/](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。 ```java 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。 ```java 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`。 ```java 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。 ```java <?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。 ```java 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： ```java 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 (?, ?) ``` [下载源码](https://drive.google.com/file/d/0B7yo2HclmjI4ZHdoLVF2Zk1Xc1E/view?usp=drive_web "download example of many to many mapping") 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！