Hibernate中运用Annotation设置联合主键

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;@Embeddablepublic 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;@Entitypublic class Teacher {private Teacher_PK teacher_PK;@Idpublic 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;@Entitypublic class Teacher {private Teacher_PK teacher_PK;private int age;@EmbeddedIdpublic 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;@Idpublic int getId() {return id;}public void setId(int id) {this.id = id;}@Idpublic 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。

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