hibernate——多表關係映射之多對多第一篇（常規）

本篇文章以Employee（員工）和Role（角色）爲例講述多對多映射關係的配置。

第一步：建表(MySQL)

#員工表
CREATE TABLE employee (
ID INT(2) PRIMARY KEY AUTO_INCREMENT,
NAME CHAR(10) NOT NULL,
AGE INT(2) NOT NULL);

#角色表
CREATE TABLE role (
ID INT(2) PRIMARY KEY AUTO_INCREMENT,
NAME CHAR(10) NOT NULL);

#關係表
CREATE TABLE employee_role_table (
EMPLOYEE_ID INT(2),
ROLE_ID INT(2),
FOREIGN KEY(EMPLOYEE_ID) REFERENCES employee(ID),
FOREIGN KEY(ROLE_ID) REFERENCES role(ID));

第二步：編寫實體類

//Employee.java
public class Employee implements Serializable {

	private static final long serialVersionUID = 1L;
	private Integer id;
	private String name;
	private Integer age;
	private Set<Role> roles = new HashSet<Role>();
	
	public Employee(Integer id, String name, Integer age) {
		super();
		this.id = id;
		this.name = name;
		this.age= age;
	}
	public Employee() {
		super();
	}
	
	public Set<Role> getRoles() {
		return roles;
	}
	public void setRoles(Set<Role> roles) {
		this.roles = roles;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
}

//Role.java
public class Role implements Serializable {

	private static final long serialVersionUID = 1L;
	private Integer id;
	private String name;
	private Set<Employee> employees = new HashSet<>();
	
	public Role(Integer id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	public Role() {
		super();
	}
	public Set<Employee> getEmployees() {
		return employees;
	}
	public void setEmployees(Set<Employee> employees) {
		this.employees = employees;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

第三步：實體類與數據表映射文件

<!-- Employee.hbm.xml --> 
<hibernate-mapping package="com.aha.hibernate.entity">
    <class name="Employee" table="employee">
        <id name="id" column="ID">
            <generator class="native"></generator>
        </id>
        <property name="name" column="NAME"></property>
        <property name="age" column="AGE"></property>
            
        <set name="roles" table="employee_role_table ">
            <!-- 此處應填寫關係表中的字段名 -->
            <key column="EMPLOYEE_ID"></key>
            <!-- 此處應填寫關係表中的字段名 -->
            <many-to-many class="com.aha.hibernate.entity.Role" column="ROLE_ID"></many-to-many>
        </set>
            
    </class>
</hibernate-mapping>

<!-- Role.hbm.xml --> 
<hibernate-mapping package="com.aha.hibernate.entity">
    <class name="Role" table="role">
        <id name="id" column="ID">
            <generator class="native"></generator>
        </id>
        <property name="name" column="NAME"></property>
        <!--
            多對多映射不允許雙方都對其進行維護，必須一方放棄維護，即inverse="true"
            根據實際業務選擇哪一方放棄維護，員工-角色應選擇角色放棄維護。   
        -->
        <set name="employees" table="employee_role_table" inverse="true">
            <!-- 此處應填寫關係表中的字段名 -->
            <key column="ROLE_ID"></key>
            <!-- 此處應填寫關係表中的字段名 -->
            <many-to-many class="com.aha.hibernate.entity.Employee" column="EMPLOYEE_ID"></many-to-many>
        </set>
    </class>
</hibernate-mapping>