Spring Data Jpa设置联合主键

对于三种比较常见的SpringBoot持久层框架中，作者最喜欢的Spring Data Jpa,因为相比于Hibernate和MyBatis，它更符合ORM的理念，更多的使用注解来实现各种持久化操作，简单易上手，而且也不需要写很多的相关文件，有点Spring和SpringBoot之间那么点意思，当然对于一些复杂CAUD场景可能会有不太方便的地方，但是对于需要快速开发的小项目时，它显得极为合适。

言归正传，前几天在快速搭建的一个日志分析系统，最后对数据表进行重构的时候，需要设置联合主键，遇到了一些问题，最后发现并只不是在实体类的属性中添加多个@Id,所以在此记下：

两种实现方法

1.@IdClass + @Id

1.1联合主键类

首先依照以下规则写一个包含实体类所有组成联合主键的字段的联合主键类，

继承Serializable接口进行序列化
重写hashCode()和equals()方法

有一个无参构造函数

/**
* Description 联合主键类
* Author Cloudr 
* Date 2020/4/26 22:50
**/
public class PhoneMultiKeys implements Serializable {

    private String band;
    private String series;
    private int size;

    public PhoneMultiKeys() {
    }

    public PhoneMultiKeys(String band, String series, int size) {
        this.band = band;
        this.series = series;
        this.size = size;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public String getBand() {
        return band;
    }

    public void setBand(String band) {
        this.band = band;
    }

    public String getSeries() {
        return series;
    }

    public void setSeries(String series) {
        this.series = series;
    }

    @Override
    public int hashCode(){
        int code=17;
        code=code*31+(band!=null?band.hashCode():0);
        code=code*31+(series!=null?series.hashCode():0);
        code=code*31+(int)size;
        return code;
    }

    @Override
    public boolean equals(Object object){
        if(object==null)
            return false;
        if (!(object instanceof PhoneMultiKeys))
            return false;
        PhoneMultiKeys obj=(PhoneMultiKeys)object;
        if(obj.band.equals(band)&&obj.series.equals(series))
            return true;
        return false;
    }
}

1.2实体类

如常编写实体类

注意使用@IdClass,参数为对应的联合主键类
@Id注解正常使用

重写equals()和hashCode()

/**
* Description 实体类
* Author Cloudr 
* Date 2020/4/26 22:49
**/
@Entity
@Table(name = "phoneTestFroMultiKeys")
@IdClass(PhoneMultiKeys.class)
public class Phone implements Serializable {
    @Id
    private String band;
    @Id
    private String series;
    @Id
    private int size;
    private String model;

    public Phone() {
    }

    public Phone(String band, String series, String model,int size) {
        this.band = band;
        this.series = series;
        this.model = model;
        this.size=size;
    }

    public String getBand() {
        return band;
    }

    public void setBand(String band) {
        this.band = band;
    }

    public String getSeries() {
        return series;
    }

    public void setSeries(String series) {
        this.series = series;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    @Override
    public String toString() {
        return "Phone{" +
                "band='" + band + '\'' +
                ", series='" + series + '\'' +
                ", size=" + size +
                ", model='" + model + '\'' +
                '}';
    }
}

1.3测试

Dao层

JpaRepository<T,TD> //TD类型测试过String、Integer、以及无关的Date和Object都可以，所以任何类型都可以？

public interface PhoneDao extends JpaRepository<Phone, Object> { 

    public Optional<Phone> findByBandAndSeriesAndSize(String band, String series, int size);

}

Service层

@Service
public interface PhoneService {

    void saveALl(List<Phone> phoneList);

}

@Service
public class PhoneServiceImpl implements PhoneService {

    @Resource
    private PhoneDao phoneDao;

    @Override
    public void saveALl(List<Phone> phoneList) {
        phoneDao.saveAll(phoneList);
    }

    public Optional<Phone> findByBandAndSeriesAndSize(String mi, String mix, int i) {
        return phoneDao.findByBandAndSeriesAndSize(mi,mix,i);
    }
}

测试

//SUCCEED
@Test
void TestSaveList() {
    Book book1 = new Book("cc1", "aa");
    Book book2 = new Book("cc2", "aa");
    List<Book> list = new ArrayList<>();
    list.add(book1);
    list.add(book2);
    bookService.saveAll(list);
}

2.@Embeddable + @EmbedId

2.1 联合主键类

加入@Embeddable
序列化

无参构造函数

UserPK是一种命名风格并不是协议

@Embeddable
public class UserPK implements Serializable  {
    private String userId;
    private String userName;

    public UserPK() {
    }

    public UserPK(String userId, String userName) {
        this.userId = userId;
        this.userName = userName;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        UserPK userPK = (UserPK) o;
        return userId.equals(userPK.userId) &&
                userName.equals(userPK.userName);
    }

    @Override
    public int hashCode() {
        return Objects.hash(userId, userName);
    }
}

2.2 实体类

使用@EmbeddedId标注Id

Id类型为UserPK

@Entity
@Table(name = "user_test")
public class User implements Serializable {
    @EmbeddedId
    private UserPK id;
    private String nickName;

    public User() {
    }

    public User(UserPK id, String nickName) {
        this.id = id;
        this.nickName = nickName;
    }

    public UserPK getId() {
        return id;
    }

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

    public String getNickName() {
        return nickName;
    }

    public void setNickName(String nickName) {
        this.nickName = nickName;
    }
}

Dao层

JpaRepository<T, TD> //TD类型为联合主键类

1
2
3

public interface UserRepository extends JpaRepository<User, UserPK> {

}

2.3 测试

@Resource
private UserRepository userDao;
@Test
void TestUserWithMultiKeys() {
    User user = new User(new UserPK("123", "Lou"), "cc");
    userDao.save(user);
    logger.info("存储成功");
}

总结

作者猜测Jpa之所以不能只在实体类中添加多个@Id实现联合主键是因为可能只靠注释可能在一些情况下不够准确，也可能底层没有做的特别完善，期待Jpa后续的更新。而在联合主键类中必须重写equals()和hashCode()以及都必须实现序列化都已在一定程度上印证了这一点。当然这些都是猜测，期望和各位的交流。
关于以上两种方法，@Embeddable + @EmbedId更符合面向对象的设计思想，将联合主键直接封装成一个类，@IdClass + @Id更直观，目前作者还不知道其中的具体差异。