Hibernate中使用Annotation设置联合主键

在Hibernate中，有3中方法可以设置联合主键
1：使用Embeddable
此方法是在主键类前加入@Embeddable
然后在主键类对象的get方法上加入@Id即可

示例：

//此类为Teacher的主键类
package com.freedom.pk;

import java.io.Serializable;

import javax.persistence.Embeddable;

@Embeddable
public class Teacher_PK implements Serializable {
	private int id;
	private String name;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

package com.freedom.model;

import javax.persistence.Entity;
import javax.persistence.Id;

import com.freedom.pk.Teacher_PK;

@Entity
public class Teacher {

	private Teacher_PK teacher_PK;

	@Id
	public Teacher_PK getTeacher_PK() {
		return teacher_PK;
	}

	public void setTeacher_PK(Teacher_PK teacher_PK) {
		this.teacher_PK = teacher_PK;
	}

	private int age;

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
}

2：使用EmbeddedId
此方法比较简单，只需在主键类对象的get方法上加入@EmbeddedId即可

示例：

package com.freedom.pk;

import java.io.Serializable;

public class Teacher_PK implements Serializable {
	private int id;
	private String name;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

package com.freedom.model;

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;

import com.freedom.pk.Teacher_PK;

@Entity
public class Teacher {

	private Teacher_PK teacher_PK;
	private int age;

	@EmbeddedId
	public Teacher_PK getTeacher_PK() {
		return teacher_PK;
	}

	public void setTeacher_PK(Teacher_PK teacher_PK) {
		this.teacher_PK = teacher_PK;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
}

3：使用IdClass
在类前面加入@IdClass(value=xxxxx.class)   xxxxx为主键类的类名，当只有一个参数时，我们可以直接省略写为@IdClass(xxxxx.class)
并且在主键元素的每个对象前加入@Id
示例：

package com.freedom.pk;

import java.io.Serializable;

public class Teacher_PK implements Serializable {
	private int id;
	private String name;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

package com.freedom.model;

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;

import com.freedom.pk.Teacher_PK;

@Entity
@IdClass(Teacher_PK.class)
public class Teacher {

	private int id;
	private String name;
	private int age;

	@Id
	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	@Id
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
}

我们比较常用的是第二种和第三中方法，第一种一般不用。