hibernate——多表关系映射之多对多第二篇（主键外的其它字段映射）

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

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 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 getEmployeeAndRoles() {
		return employeeAndRoles;
	}
	public void setEmployeeAndRoles(Set 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 employeeAndRoles = new HashSet<>();
	
	public Role(Integer id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	public Role() {
		super();
	}
	public Set getEmployeeAndRoles() {
		return employeeAndRoles;
	}
	public void setEmployeeAndRoles(Set 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，这里会用到等标签，拭目以待。

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。