SpringData JPA快速上手之关联查询及JPQL语句书写详解

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

@Data
public class Account {
    int id;
    String username;
    String password;
}

@Data
@Entity   //表示这个类是一个实体类
@Table(name = "account")    //对应的数据库中表名称
public class Account {
    @GeneratedValue(strategy = GenerationType.IDENTITY)   //生成策略，这里配置为自增
    @Column(name = "id")    //对应表中id这一列
    @Id     //此属性为主键
    int id;
    @Column(name = "username")   //对应表中username这一列
    String username;
    @Column(name = "password")   //对应表中password这一列
    String password;
}

spring:
  jpa:
    #开启SQL语句执行日志信息
    show-sql: true
    hibernate:
      #配置为检查数据库表结构，没有时会自动创建
      ddl-auto: update

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {
}

@Resource
AccountRepository repository;
@Test
void contextLoads() {
    Account account = new Account();
    account.setUsername("小红");
    account.setPassword("1234567");
    System.out.println(repository.save(account).getId());   //使用save来快速插入数据，并且会返回插入的对象，如果存在自增ID，对象的自增id属性会自动被赋值，这就很方便了
}

@Test
void contextLoads() {
  	//默认通过通过ID查找的方法，并且返回的结果是Optional包装的对象，非常人性化
    repository.findById(1).ifPresent(System.out::println);
}

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {
    //按照表中的规则进行名称拼接，不用刻意去记，IDEA会有提示
    List<Account> findAllByUsernameLike(String str);
}

@Test
void contextLoads() {
    repository.findAllByUsernameLike("%明%").forEach(System.out::println);
}

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {
    List<Account> findAllByUsernameLike(String str);
    Account findByIdAndUsername(int id, String username);
    //也可以使用Optional类进行包装，Optional<Account> findByIdAndUsername(int id, String username);
}

@Test
void contextLoads() {
    System.out.println(repository.findByIdAndUsername(1, "小明"));
}

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {
    List<Account> findAllByUsernameLike(String str);
    Account findByIdAndUsername(int id, String username);
    //使用exists判断是否存在
    boolean existsAccountById(int id);
}

@Data
@Entity
@Table(name = "users_detail")
public class AccountDetail {
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    int id;
    @Column(name = "address")
    String address;
    @Column(name = "email")
    String email;
    @Column(name = "phone")
    String phone;
    @Column(name = "real_name")
    String realName;
}

@Data
@Entity
@Table(name = "users")
public class Account {
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    @Id
    int id;
    @Column(name = "username")
    String username;
    @Column(name = "password")
    String password;
    @JoinColumn(name = "detail_id")   //指定存储外键的字段名称
    @OneToOne    //声明为一对一关系
    AccountDetail detail;
}

@Test
void pageAccount() {
    repository.findById(1).ifPresent(System.out::println);
}

@JoinColumn(name = "detail_id")
@OneToOne(fetch = FetchType.LAZY)    //将获取类型改为LAZY
AccountDetail detail;

@Transactional   //懒加载属性需要在事务环境下获取，因为repository方法调用完后Session会立即关闭
@Test
void pageAccount() {
    repository.findById(1).ifPresent(account -> {
        System.out.println(account.getUsername());   //获取用户名
        System.out.println(account.getDetail());  //获取详细信息（懒加载）
    });
}

@JoinColumn(name = "detail_id")
@OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL) //设置关联操作为ALL
AccountDetail detail;

@Test
void addAccount(){
    Account account = new Account();
    account.setUsername("Nike");
    account.setPassword("123456");
    AccountDetail detail = new AccountDetail();
    detail.setAddress("重庆市渝中区解放碑");
    detail.setPhone("1234567890");
    detail.setEmail("73281937@qq.com");
    detail.setRealName("张三");
  	account.setDetail(detail);
    account = repository.save(account);
    System.out.println("插入时，自动生成的主键ID为："+account.getId()+"，外键ID为："+account.getDetail().getId());
}

@JoinColumn(name = "uid")  //注意这里的name指的是Score表中的uid字段对应的就是当前的主键，会将uid外键设置为当前的主键
@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.REMOVE)   //在移除Account时，一并移除所有的成绩信息，依然使用懒加载
List<Score> scoreList;

@Data
@Entity
@Table(name = "users_score")   //成绩表，注意只存成绩，不存学科信息，学科信息id做外键
public class Score {
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    @Id
    int id;
    @OneToOne   //一对一对应到学科上
    @JoinColumn(name = "cid")
    Subject subject;
    @Column(name = "socre")
    double score;
    @Column(name = "uid")
    int uid;
}

@Data
@Entity
@Table(name = "subjects")   //学科信息表
public class Subject {
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "cid")
    @Id
    int cid;
    @Column(name = "name")
    String name;
    @Column(name = "teacher")
    String teacher;
    @Column(name = "time")
    int time;
}

@Transactional
@Test
void test() {
    repository.findById(1).ifPresent(account -> {
        account.getScoreList().forEach(System.out::println);
    });
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "tid")   //存储教师ID的字段，和一对一是一样的，也会当前表中创个外键
Teacher teacher;

@Data
@Entity
@Table(name = "teachers")
public class Teacher {
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Id
    int id;
    @Column(name = "name")
    String name;
    @Column(name = "sex")
    String sex;
}

@Transactional
@Test
void test() {
    repository.findById(3).ifPresent(account -> {
        account.getScoreList().forEach(score -> {
            System.out.println("课程名称："+score.getSubject().getName());
            System.out.println("得分："+score.getScore());
            System.out.println("任课教师："+score.getSubject().getTeacher().getName());
        });
    });
}

@ManyToMany(fetch = FetchType.LAZY)   //多对多场景
@JoinTable(name = "teach_relation",     //多对多中间关联表
        joinColumns = @JoinColumn(name = "cid"),    //当前实体主键在关联表中的字段名称
        inverseJoinColumns = @JoinColumn(name = "tid")   //教师实体主键在关联表中的字段名称
)
List<Teacher> teacher;

@Repository
public interface AccountRepository extends JpaRepository<Account, Integer> {
    @Transactional    //DML操作需要事务环境，可以不在这里声明，但是调用时一定要处于事务环境下
    @Modifying     //表示这是一个DML操作
    @Query("update Account set password = ?2 where id = ?1") //这里操作的是一个实体类对应的表，参数使用?代表，后面接第n个参数
    int updatePasswordById(int id, String newPassword);
}

@Test
void updateAccount(){
    repository.updatePasswordById(1, "654321");
}

@Transactional
@Modifying
@Query(value = "update users set password = :pwd where username = :name", nativeQuery = true) //使用原生SQL，和Mybatis一样，这里使用 :名称 表示参数，当然也可以继续用上面那种方式。
int updatePasswordByUsername(@Param("name") String username,   //我们可以使用@Param指定名称
                             @Param("pwd") String newPassword);

@Test
void updateAccount(){
    repository.updatePasswordByUsername("Admin", "654321");
}