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举例讲解Java的Hibernate框架中的多对一和一对多映射

作者：Eve Cole 更新时间：2025-06-30 20:00:04

多对一（Many-to-One）映射
多对一（many-to-one）关联是最常见的关联关系，其中一个对象可以与多个对象相关联。例如，一个相同的地址对象可以与多个雇员的对象相关联。

定义RDBMS表：
考虑一个情况，我们需要员工记录存储在EMPLOYEE表，将有以下结构：

create table EMPLOYEE (  id INT NOT NULL auto_increment,  first_name VARCHAR(20) default NULL,  last_name VARCHAR(20) default NULL,  salary   INT default NULL,  address  INT NOT NULL,  PRIMARY KEY (id));

此外，许多员工都可以有相同的地址，所以这种关联可以使用许多一对一的关联呈现。我们将存储地址相关的信息在一个单独的表，该表具有以下结构：

create table ADDRESS (  id INT NOT NULL auto_increment,  street_name VARCHAR(40) default NULL,  city_name VARCHAR(40) default NULL,  state_name VARCHAR(40) default NULL,  zipcode VARCHAR(10) default NULL,  PRIMARY KEY (id));

同时创建RBDMS表，并让他们准备下一个实现。

定义POJO类：
让我们实现一个POJO类员工将被用于保存与EMPLOYEE表的对象和其地址类型的变量。

import java.util.*;public class Employee{  private int id;  private String firstName;   private String lastName;    private int salary;  private Address address;  public Employee() {}  public Employee(String fname, String lname,           int salary, Address address ) {   this.firstName = fname;   this.lastName = lname;   this.salary = salary;   this.address = address;  }  public int getId() {   return id;  }  public void setId( int id ) {   this.id = id;  }  public String getFirstName() {   return firstName;  }  public void setFirstName( String first_name ) {   this.firstName = first_name;  }  public String getLastName() {   return lastName;  }  public void setLastName( String last_name ) {   this.lastName = last_name;  }  public int getSalary() {   return salary;  }  public void setSalary( int salary ) {   this.salary = salary;  }  public Address getAddress() {   return address;  }  public void setAddress( Address address ) {   this.address = address;  }}

我们需要定义相应的地址表，这样地址对象可以存储和检索到地址表中的另一个POJO类。

import java.util.*;public class Address{  private int id;  private String street;     private String city;     private String state;    private String zipcode;   public Address() {}  public Address(String street, String city,          String state, String zipcode) {   this.street = street;    this.city = city;    this.state = state;    this.zipcode = zipcode;   }  public int getId() {   return id;  }  public void setId( int id ) {   this.id = id;  }  public String getStreet() {   return street;  }  public void setStreet( String street ) {   this.street = street;  }  public String getCity() {   return city;  }  public void setCity( String city ) {   this.city = city;  }  public String getState() {   return state;  }  public void setState( String state ) {   this.state = state;  }  public String getZipcode() {   return zipcode;  }  public void setZipcode( String zipcode ) {   this.zipcode = zipcode;  }  }

定义Hibernate映射文件：
开发我们的映射文件，可指示Hibernate如何定义的类映射到数据库表。<many-to-one>进行元素将被用来定义规则建立Employee和Address实体之间的多对一关系。

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC  "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping>  <class name="Employee" table="EMPLOYEE">   <meta attribute="class-description">     This class contains the employee detail.    </meta>   <id name="id" type="int" column="id">     <generator/>   </id>   <property name="firstName" column="first_name" type="string"/>   <property name="lastName" column="last_name" type="string"/>   <property name="salary" column="salary" type="int"/>   <many-to-one name="address" column="address"     not-null="true"/>  </class>  <class name="Address" table="ADDRESS">   <meta attribute="class-description">     This class contains the address detail.    </meta>   <id name="id" type="int" column="id">     <generator/>   </id>   <property name="street" column="street_name" type="string"/>   <property name="city" column="city_name" type="string"/>   <property name="state" column="state_name" type="string"/>   <property name="zipcode" column="zipcode" type="string"/>  </class></hibernate-mapping>

应该保存的映射文件中的格式<classname>.hbm.xml。保存映射文件中的文件Employee.hbm.xml。已经熟悉了大部分的映射细节，但让我们再次看看映射文件中的所有元素：

映射文档是具有<hibernate-mapping>为对应于每一个类包含2个<class>元素的根元素的XML文档。

<class>元素被用于定义数据库表从一个Java类特定的映射。 Java类名指定使用class元素的name属性和使用表属性数据库表名指定。

<meta>元素是可选元素，可以用来创建类的描述。

<id>元素映射在类中的唯一ID属性到数据库表的主键。 id元素的name属性是指属性的类和column属性是指在数据库表中的列。 type属性保存了Hibernate映射类型，这种类型的映射将会从Java转换为SQL数据类型。

id元素内<generator>元素被用来自动生成的主键值。将生成元素class属性设置为原生让Hibernate拾取无论是identity，sequence或者hilo的算法来创建主键根据底层数据库的支持能力。

<property>元素用于一个Java类的属性映射到数据库表中的列。元素的name属性是指属性的类和column属性是指在数据库表中的列。 type属性保存了Hibernate映射类型，这种类型的映射将会从Java转换为SQL数据类型。

<many-to-one>进行元素是用来设置EMPLOYEE和地址的实体之间的关系。name属性被设置为在父类中定义的变量，在我们的情况下，它是地址。列属性用于在父表EMPLOYEE集的列名。

最后，我们将创建应用程序类的main（）方法来运行应用程序。我们将使用这个应用程序，以节省一些employee连同的记录他们的地址，然后我们将申请CRUD操作上的记录。

import java.util.*; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee {  private static SessionFactory factory;   public static void main(String[] args) {   try{     factory = new Configuration().configure().buildSessionFactory();   }catch (Throwable ex) {      System.err.println("Failed to create sessionFactory object." + ex);     throw new ExceptionInInitializerError(ex);    }   ManageEmployee ME = new ManageEmployee();   /* Let us have one address object */   Address address = ME.addAddress("Kondapur","Hyderabad","AP","532");   /* Add employee records in the database */   Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, address);   /* Add another employee record in the database */   Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, address);   /* List down all the employees */   ME.listEmployees();   /* Update employee's salary records */   ME.updateEmployee(empID1, 5000);   /* Delete an employee from the database */   ME.deleteEmployee(empID2);   /* List down all the employees */   ME.listEmployees();  }  /* Method to add an address record in the database */  public Address addAddress(String street, String city,                String state, String zipcode) {   Session session = factory.openSession();   Transaction tx = null;   Integer addressID = null;   Address address = null;   try{     tx = session.beginTransaction();     address = new Address(street, city, state, zipcode);     addressID = (Integer) session.save(address);      tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }   return address;  }  /* Method to add an employee record in the database */  public Integer addEmployee(String fname, String lname,                int salary, Address address){   Session session = factory.openSession();   Transaction tx = null;   Integer employeeID = null;   try{     tx = session.beginTransaction();     Employee employee = new Employee(fname, lname, salary, address);     employeeID = (Integer) session.save(employee);      tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }   return employeeID;  }  /* Method to list all the employees detail */  public void listEmployees( ){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     List employees = session.createQuery("FROM Employee").list();      for (Iterator iterator =               employees.iterator(); iterator.hasNext();){      Employee employee = (Employee) iterator.next();       System.out.print("First Name: " + employee.getFirstName());       System.out.print(" Last Name: " + employee.getLastName());       System.out.println(" Salary: " + employee.getSalary());      Address add = employee.getAddress();      System.out.println("Address ");      System.out.println(" Street: " + add.getStreet());      System.out.println(" City: " + add.getCity());      System.out.println(" State: " + add.getState());      System.out.println(" Zipcode: " + add.getZipcode());     }     tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }  /* Method to update salary for an employee */  public void updateEmployee(Integer EmployeeID, int salary ){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     Employee employee =           (Employee)session.get(Employee.class, EmployeeID);      employee.setSalary( salary );     session.update(employee);     tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }  /* Method to delete an employee from the records */  public void deleteEmployee(Integer EmployeeID){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     Employee employee =           (Employee)session.get(Employee.class, EmployeeID);      session.delete(employee);      tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }}

编译和执行：
下面是步骤来编译并运行上述应用程序。请确保已在进行的编译和执行之前，适当地设置PATH和CLASSPATH。

  • 创建hibernate.cfg.xml配置文件中配置章节解释。
  • 创建Employee.hbm.xml映射文件，如上图所示。
  • 创建Employee.java源文件，如上图所示，并编译它。
  • 创建Address.java源文件，如上图所示，并编译它。
  • 创建ManageEmployee.java源文件，如上图所示，并编译它。
  • 执行ManageEmployee二进制文件来运行程序。

在屏幕上获得以下结果，并同时记录会在员工和地址表创建。

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Address    Street: Kondapur    City: Hyderabad    State: AP    Zipcode: 532First Name: Dilip Last Name: Kumar Salary: 3000Address    Street: Kondapur    City: Hyderabad    State: AP    Zipcode: 532First Name: Manoj Last Name: Kumar Salary: 5000Address    Street: Kondapur    City: Hyderabad    State: AP    Zipcode: 532

如果检查员工和地址表，就应该记录下了：

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+---------+| id | first_name | last_name | salary | address |+----+------------+-----------+--------+---------+| 1 | Manoj   | Kumar   |  5000 | 5    |+----+------------+-----------+--------+---------+1 row in set (0.00 sec)
mysql> select * from ADDRESS;
+----+-------------+-----------+------------+---------+| id | street_name | city_name | state_name | zipcode |+----+-------------+-----------+------------+---------+| 1 | Kondapur  | Hyderabad | AP     | 532   |+----+-------------+-----------+------------+---------+1 row in set (0.00 sec)


一对多（One-to-Many）映射
一对多的映射可以使用一组Java集合不包含任何重复的元素来实现。我们已经看到了如何设置映射集合在Hibernate中，所以如果你已经学会了集合（Set）映射，那么所有设置可用于一对多的映射。

集合被映射到与映射表中<set>元素，并java.util.HashSet中初始化。您可以使用Set集合在类中，有一个集合中不需要重复的元素。
RDBMS表与POJO类我们依然采用上面例子中定义好的，
定义Hibernate映射文件：
让我们指示Hibernate如何定义的类映射到数据库表的映射文件。

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC  "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping>  <class name="Employee" table="EMPLOYEE">   <meta attribute="class-description">     This class contains the employee detail.    </meta>   <id name="id" type="int" column="id">     <generator/>   </id>   <set name="certificates" cascade="all">     <key column="employee_id"/>     <one-to-many/>   </set>   <property name="firstName" column="first_name" type="string"/>   <property name="lastName" column="last_name" type="string"/>   <property name="salary" column="salary" type="int"/>  </class>  <class name="Certificate" table="CERTIFICATE">   <meta attribute="class-description">     This class contains the certificate records.    </meta>   <id name="id" type="int" column="id">     <generator/>   </id>   <property name="name" column="certificate_name" type="string"/>  </class></hibernate-mapping>

应该保存的映射文件中的格式<classname>.hbm.xml。我们保存映射文件中的文件Employee.hbm.xml。你已经熟悉了大部分的映射细节，但让我们再次看看映射文件中的所有元素：

映射文档是具有<hibernate-mapping>为对应于每一个类包含2个<class>元素的根元素的XML文档。

<class>元素被用于定义数据库表从一个Java类特定的映射。 Java类名指定使用class元素的name属性和使用表属性数据库表名指定。

<meta>元素是可选元素，可以用来创建类的描述。

<id>元素映射在类中的唯一ID属性到数据库表的主键。 id元素的name属性是指属性的类和column属性是指在数据库表中的列。 type属性保存了Hibernate映射类型，这种类型的映射将会从Java转换为SQL数据类型。

id元素内的<generator>元素被用来自动生成的主键值。将生成元素的class属性设置为原生让Hibernate拾取identity，sequence或者hilo中的算法来创建主键根据底层数据库的支持能力。

<property>元素用于一个Java类的属性映射到数据库表中的列。元素的name属性是指属性的类和column属性是指在数据库表中的列。 type属性保存了Hibernate映射类型，这种类型的映射将会从Java转换为SQL数据类型。

<set>元素设置证书和Employee类之间的关系。我们使用cascade属性中<set>元素来告诉Hibernate来保存证书的对象，同时为Employee对象。 name属性被设置为在父类中定义的变量集，在我们的例子是证书。对于每一组变量，我们需要定义在映射文件中单独的一组元素。

<key>元素是包含外键的父对象，即在证书表中的列。表EMPLOYEE。

<one-to-many>元素表示一个Employee对象涉及到很多证书的对象。

创建应用程序类：
最后，我们将创建应用程序类的main（）方法来运行应用程序。我们将使用这个应用程序，以节省一些员工连同记录证书，然后我们将应用上CRUD操作记录。

import java.util.*; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee {  private static SessionFactory factory;   public static void main(String[] args) {   try{     factory = new Configuration().configure().buildSessionFactory();   }catch (Throwable ex) {      System.err.println("Failed to create sessionFactory object." + ex);     throw new ExceptionInInitializerError(ex);    }   ManageEmployee ME = new ManageEmployee();   /* Let us have a set of certificates for the first employee */   HashSet set1 = new HashSet();   set1.add(new Certificate("MCA"));   set1.add(new Certificate("MBA"));   set1.add(new Certificate("PMP"));      /* Add employee records in the database */   Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);   /* Another set of certificates for the second employee */   HashSet set2 = new HashSet();   set2.add(new Certificate("BCA"));   set2.add(new Certificate("BA"));   /* Add another employee record in the database */   Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);   /* List down all the employees */   ME.listEmployees();   /* Update employee's salary records */   ME.updateEmployee(empID1, 5000);   /* Delete an employee from the database */   ME.deleteEmployee(empID2);   /* List down all the employees */   ME.listEmployees();  }  /* Method to add an employee record in the database */  public Integer addEmployee(String fname, String lname,                       int salary, Set cert){   Session session = factory.openSession();   Transaction tx = null;   Integer employeeID = null;   try{     tx = session.beginTransaction();     Employee employee = new Employee(fname, lname, salary);     employee.setCertificates(cert);     employeeID = (Integer) session.save(employee);      tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }   return employeeID;  }  /* Method to list all the employees detail */  public void listEmployees( ){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     List employees = session.createQuery("FROM Employee").list();      for (Iterator iterator1 =               employees.iterator(); iterator1.hasNext();){      Employee employee = (Employee) iterator1.next();       System.out.print("First Name: " + employee.getFirstName());       System.out.print(" Last Name: " + employee.getLastName());       System.out.println(" Salary: " + employee.getSalary());      Set certificates = employee.getCertificates();      for (Iterator iterator2 =              certificates.iterator(); iterator2.hasNext();){         Certificate certName = (Certificate) iterator2.next();          System.out.println("Certificate: " + certName.getName());       }     }     tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }  /* Method to update salary for an employee */  public void updateEmployee(Integer EmployeeID, int salary ){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     Employee employee =           (Employee)session.get(Employee.class, EmployeeID);      employee.setSalary( salary );     session.update(employee);     tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }  /* Method to delete an employee from the records */  public void deleteEmployee(Integer EmployeeID){   Session session = factory.openSession();   Transaction tx = null;   try{     tx = session.beginTransaction();     Employee employee =           (Employee)session.get(Employee.class, EmployeeID);      session.delete(employee);      tx.commit();   }catch (HibernateException e) {     if (tx!=null) tx.rollback();     e.printStackTrace();    }finally {     session.close();    }  }}

编译和执行：

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Certificate: MBACertificate: PMPCertificate: MCAFirst Name: Dilip Last Name: Kumar Salary: 3000Certificate: BCACertificate: BAFirst Name: Manoj Last Name: Kumar Salary: 5000Certificate: MBACertificate: PMPCertificate: MCA

如果检查员工和证书表，就应该记录下了：

mysql> select * from employee;
+----+------------+-----------+--------+| id | first_name | last_name | salary |+----+------------+-----------+--------+| 1 | Manoj   | Kumar   |  5000 |+----+------------+-----------+--------+1 row in set (0.00 sec)
mysql> select * from certificate;
+----+------------------+-------------+| id | certificate_name | employee_id |+----+------------------+-------------+| 1 | MBA       |     1 || 2 | PMP       |     1 || 3 | MCA       |     1 |+----+------------------+-------------+3 rows in set (0.00 sec)
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