hibernate——多表关系映射之多对多第二篇（主键外的其它字段映射）

向右看齐 2022-03-16 04:54 187阅读 0赞

在第一篇中写了多表映射之多对多的常规配置，即关联表中只有以其它表主键做外键的字段。[第一篇链接][Link 1]

这一篇是讲述多对多映射时，关联表如何配置非主键字段。依然以Employee与Role为例

与常规配置相比需要多编写一个实体类，例EmployeeAndRole.java，该实体类应包含Employee类和Role类对象，并提供getter、setter方法。如下：

public class EmployeeAndRole implements Serializable {
    
    	private static final long serialVersionUID = 1L;
    	private Employee employee;
    	private Role role;
    	
    	public Employee getEmployee() {
    		return employee;
    	}
    	public void setEmployee(Employee employee) {
    		this.employee = employee;
    	}
    	public Role getRole() {
    		return role;
    	}
    	public void setRole(Role role) {
    		this.role = role;
    	}
    }

编写此实体类之后，原来的Employee.java、Role.java也需要做相应修改，如下：

//Employee.java
    public class Employee implements Serializable {
    
    	private static final long serialVersionUID = 1L;
    	private Integer id;
    	private String name;
    	private Integer age;
            // 注意！！！
            // 集合应该为EmployeeAndRole实体类的集合
    	private Set<EmployeeAndRole> employeeAndRoles = new HashSet<>();
    	
    	public Employee(Integer id, String name, Integer age) {
    		super();
    		this.id = id;
    		this.name = name;
    		this.age= age;
    	}
    	public Employee() {
    		super();
    	}
    	
    	public Set<EmployeeAndRole> getEmployeeAndRoles() {
    		return employeeAndRoles;
    	}
    	public void setEmployeeAndRoles(Set<EmployeeAndRole> employeeAndRoles) {
    		this.employeeAndRoles = employeeAndRoles;
    	}
    	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;
            // 注意！！！
            // 集合应该为EmployeeAndRole实体类的集合
    	private Set<EmployeeAndRole> employeeAndRoles = new HashSet<>();
    	
    	public Role(Integer id, String name) {
    		super();
    		this.id = id;
    		this.name = name;
    	}
    	public Role() {
    		super();
    	}
    	public Set<EmployeeAndRole> getEmployeeAndRoles() {
    		return employeeAndRoles;
    	}
    	public void setEmployeeAndRoles(Set<EmployeeAndRole> employeeAndRoles) {
    		this.employeeAndRoles = employeeAndRoles;
    	}
    	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;
    	}
    }

映射配置文件同时也需要进行修改，这里会用到<composite-element>等标签，拭目以待。

<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="employeeAndRoles" table="role_user_table">
                
                <key column="employee_id"></key>
                
                <composite-element class="EmployeeAndRole">
                    
                    <parent name="employee"/>
                    
                    <many-to-one name="role" class="Role" column="role_id"></many-to-one>
                                             
                    <nested-composite-element name="employee" class="Employee">
                        
                        <property name="name" column="NAME"></property>
                    </nested-composite-element>
                    
                </composite-element>
            </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="employeeAndRoles" table="role_user_table" inverse="true">
                <key column="role_id"></key>
                <composite-element class="EmployeeAndRole">
                    <parent name="role"/>
                    <many-to-one name="employee" class="Employee" column="user_id"></many-to-one>
                </composite-element>
            </set>
        </class>
    </hibernate-mapping>

解释已在代码注释中标注，另外补充：添加字段时只在维护映射关系的一端添加配置即可，放弃维护的一端不需要配置。

[Link 1]: https://blog.csdn.net/qbs1192517180/article/details/87931092