hibernate——多表关系映射之多对多第一篇（常规）

水深无声 2022-03-16 03:14 157阅读 0赞

本篇文章以Employee（员工）和Role（角色）为例讲述多对多映射关系的配置。

第一步：建表(MySQL)

#员工表
    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);
    
    #关系表
    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：编写实体类

//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：实体类与数据表映射文件

<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 ">
                
                <key column="EMPLOYEE_ID"></key>
                
                <many-to-many class="com.aha.hibernate.entity.Role" column="ROLE_ID"></many-to-many>
            </set>
                
        </class>
    </hibernate-mapping>
    
     
    <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>
            
            <set name="employees" table="employee_role_table" inverse="true">
                
                <key column="ROLE_ID"></key>
                
                <many-to-many class="com.aha.hibernate.entity.Employee" column="EMPLOYEE_ID"></many-to-many>
            </set>
        </class>
    </hibernate-mapping>