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整合JPA

HeJin大约 2 分钟Spring全家桶SpringBoot精讲细讲

JPA顾名思义就是Java Persistence API的意思，是JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。

JPA是一种规范。Spring Data JPA规范了怎么操作持久层。Hibernate框架遵循了这个规范。

添加依赖

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

配置文件

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/test?useSSL=true&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
    username: root
    password: 123456
  jpa:
    database-platform: org.hibernate.dialect.MySQL8Dialect
    show-sql: true
    hibernate:
      # 程序启动时删除并且创建实体类对应的表
      ddl-auto: create

编写接口继承JpaRepository或者CrudRepository

JpaRepository接口

public interface PersonRepository extends JpaRepository<Person,Long> {
}

CrudRepository接口

public interface PersonRepository2 extends CrudRepository<Person,Long> {
}

简单增删改查

@SpringBootTest
class Springboot01ApplicationTests {
    @Autowired
    private PersonRepository personRepository;

    @Test
    void contextLoads() {
        Person person = new Person(1L, "张三", "123456", "2d2e25", new Date(), new Date(), new Date());
        personRepository.save(person);
        personRepository.findAll().forEach(System.out::println);
    }

}
image-20210511200943075
image-20210511200943075

数据库中也有了一张表。

image-20210511201139764
image-20210511201139764

自定义方法

public interface PersonRepository extends JpaRepository<Person,Long> {
    /**
     * 通过username查询Person
     * @param username 用户名
     * @return
     */
    List<Person> findByUsername(String username);
}

测试

@SpringBootTest
class Springboot01ApplicationTests {
    @Autowired
    private PersonRepository personRepository;

    @Test
    void contextLoads() {
        Person person = new Person(1L, "张三", "123456", "2d2e25", new Date(), new Date(), new Date());
        personRepository.save(person);
        personRepository.findAll().forEach(System.out::println);


        List<Person> personList = personRepository.findByUsername("张三");
        personList.forEach(System.out::println);
    }

}
image-20210511204109242
image-20210511204109242

分页

@SpringBootTest
class Springboot01ApplicationTests {
    @Autowired
    private PersonRepository personRepository;

    @Test
    void contextLoads() {
        Person person1 = new Person(1L, "张三", "123456", "2d2e25", new Date(), new Date(), new Date());
        Person person2 = new Person(2L, "张三风", "123456", "2d2e25", new Date(), new Date(), new Date());
        Person person3 = new Person(3L, "lisi", "123456", "2d2e25", new Date(), new Date(), new Date());
        personRepository.saveAll(Arrays.asList(person1, person2, person3));

        List<Person> personList = personRepository.findAll(PageRequest.of(0, 2)).getContent();
        personList.forEach(System.out::println);

    }
image-20210511211125119
image-20210511211125119
image-20210511205155076
image-20210511205155076

hql

单对象查询

public interface PersonRepository extends JpaRepository<Person,Long> {
    /**
     * hql
     * @param num1
     * @param num2
     * @return
     */
    @Query(value = "from Person where id > :num1 and id < :num2")
    List<Person> find(@Param("num1") Long num1, @Param("num2") Long num2);

}

测试

@SpringBootTest
class Springboot01ApplicationTests {

    @Autowired
    private User user;

    @Autowired
    private PersonRepository personRepository;

    @Test
    void contextLoads() {
        Person person1 = new Person(1L, "张三", "123456", "2d2e25", new Date(), new Date(), new Date());
        Person person2 = new Person(2L, "张三风", "123456", "2d2e25", new Date(), new Date(), new Date());
        Person person3 = new Person(3L, "lisi", "123456", "2d2e25", new Date(), new Date(), new Date());
        personRepository.saveAll(Arrays.asList(person1, person2, person3));

        List<Person> people = personRepository.find(1L,3L);
        people.forEach(System.out::println);

    }

}
image-20210512092846240
image-20210512092846240

多对象查询

public interface PersonRepository extends JpaRepository<Person,Long> {   
	/**
     * hql
     * @param did
     * @return
     */
    @Query(value = "from Person p left join Dept d on d.id = p.deptId where d.id = :did")
    List<Person> find(@Param("did") Long did);
}

普通SQL查询

public interface PersonRepository extends JpaRepository<Person,Long> {
    /**
     * 普通SQL
     * @param did
     * @return
     */
    @Query(value = "select * from t_user p left join t_dept d on d.id = p.dept_id where d.id = ?1", nativeQuery = true)
    List<Person> find( Long did);

}
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