9.annotation配置联合主键

3种联合主键方法：

Annotation

i. @Embeddble @Id

ii. @EmbeddedID（*）

iii. @ Id @IdClass（*）

 

第一种@Embeddble @Id

主键类：TeacherPk类中包含联合主键id,name.这个类必须实行implements Serializable。

import javax.persistence.Embeddable;

@Embeddable 
public class TeacherPk implements Serializable{
    private String name;
    private int id;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    
}

实体bean:Teacher.包含TeacherPk属性，并将get方法设置为@Id

@Entity
public class Teacher {
    private TeacherPk tpk;
    private String title;
    private Date birthDate;
    @Id
    public TeacherPk getTpk() {
        return tpk;
    }
    public void setTpk(TeacherPk tpk) {
        this.tpk = tpk;
    }
    @Temporal(value = TemporalType.DATE)
    public Date getBirthDate() {
        return birthDate;
    }
    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }
    /*
     * public String getName() { return name; }
     */

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

    /*
     * @Id public int getId() { return id; }
     * 
     * public void setId(int id) { this.id = id; }
     */
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}

第二种@EmbeddedId直接放在组件上。去掉TeacherPk的注解

public class Teacher {
    private TeacherPk tpk;
    private String title;
    private Date birthDate;
    @EmbeddedId
    public TeacherPk getTpk() {
        return tpk;
    }
    public void setTpk(TeacherPk tpk) {
        this.tpk = tpk;
    }
    @Temporal(value = TemporalType.DATE)
    public Date getBirthDate() {
        return birthDate;
    }
    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }
    /*
     * public String getName() { return name; }
     */

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

    /*
     * @Id public int getId() { return id; }
     * 
     * public void setId(int id) { this.id = id; }
     */
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}

 

但是，在实际的项目中，表中应该有id,name.所有Teacher中应该用getter和setter方法才对。所以，第三种方法，将保留id,name去掉TeacherPk这个组件。

第三种@ Id @IdClass（*）

@Entity
@IdClass(value=TeacherPk.class)
public class Teacher {
    private String name;
    private int id;
    private String title;
    private Date birthDate;

    @Temporal(value = TemporalType.DATE)
    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }
    @Id
    public String getName() {
        return name;
    }

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

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

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

TeacherPk是需要的，在以后查询的时候，需要“主键对象”。