SpringBoot 数据访问-jpa
JPA
JPA（Java Persistence API）是 Java 持久化规范，它为关系型数据库访问提供了一种对象关系映射（ORM）的解决方案。在 Spring Boot 中，结合 JPA 可以极大地简化数据库访问的开发工作。
@Entity注解：用于标记一个 Java 类为实体类，该类将与数据库中的表对应。
package com.ktjiaoyu.crm.pojo;
import javax.persistence.*;
import java.io.Serializable;
@Entity
@Table(name = "sys_user")
//@NamedQueries(@NamedQuery(name = "User.findUsersByName", query = "select u from User u where u.usrName= ?1"))
public class User implements Serializable {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)@Column(name = "usr_id")private Long usrId;@Column(name = "usr_name")private String usrName;@Column(name = "usr_password")private String usrPassword;
// @Column(name = "usr_role_id")
// private Long usrRoleId;@ManyToOne(targetEntity = Role.class)@JoinColumn(name = "usr_role_id")private Role role;@Column(name = "usr_flag")private Integer usrFlag;public User() {}public User(String usrName, String usrPassword, Role role, Integer usrFlag) {this.usrName = usrName;this.usrPassword = usrPassword;this.role = role;this.usrFlag = usrFlag;}public Long getUsrId() {return usrId;}public void setUsrId(Long usrId) {this.usrId = usrId;}public String getUsrName() {return usrName;}public void setUsrName(String usrName) {this.usrName = usrName;}public String getUsrPassword() {return usrPassword;}public void setUsrPassword(String usrPassword) {this.usrPassword = usrPassword;}public Role getRole() {return role;}public void setRole(Role role) {this.role = role;}public Integer getUsrFlag() {return usrFlag;}public void setUsrFlag(Integer usrFlag) {this.usrFlag = usrFlag;}
} @Repository注解：用于标记数据访问层的组件类，通常用于数据库操作的方法定义
package com.ktjiaoyu.crm.repository;
import com.ktjiaoyu.crm.pojo.User;
import org.springframework.data.jpa.repository.JpaRepository;
public interface UserRepository extends JpaRepository<User,Long>{// List<User> findByUsrNameLike(String usrName);
//
// @Query(value = "select u from User u where u.usrRoleId=:roleId")
// List<User> findByRoleId(@Param("roleId") Long roleId);
//
// @Transactional(timeout = 10)
// @Modifying
// @Query("update User u set u.usrName=?1 where u.usrId=?2")
// int modifyNameById(String usrName,Long roleId);
//
// List<User> findUsersByName(String usrName);
//
// @Query("select u from User u where u.usrRoleId=?1")
// Page<User> findPageByUsrRoleId(Long roleId, Pageable pageable);
}
JpaRepository接口：Spring Data JPA 提供的核心接口，继承自PagingAndSortingRepository和CrudRepository，提供了丰富的数据库操作方法，如增删改查、分页和排序等。
配置
在application.properties或application.yml文件中进行数据库连接等配置。
spring.application.name=SpringBootJPA
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/crm?useUnicode=true&characterEncoding=utf-8
spring.datasource.username=root
spring.datasource.password=123456
#??JPA????
spring.jpa.properties.hibernate.hbm2ddl.auto=update
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true测试
package com.ktjiaoyu.crm;import com.ktjiaoyu.crm.pojo.Role;
import com.ktjiaoyu.crm.pojo.User;
import com.ktjiaoyu.crm.repository.RoleRepository;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;import javax.annotation.Resource;
//@RunWith(SpringRunner.class)
@SpringBootTest
public class UserRepositoryTester {
// @Resource
// private UserRepository userRepository;@Resourceprivate RoleRepository roleRepository;@Testpublic void testAdd(){//测试级联新增Role role=new Role("测试角色","演示级联新增角色和用户",1);User user1=new User("测试用户1","123456",role,1);User user2=new User("测试用户2","123456",role,1);role.getUsers().add(user1);role.getUsers().add(user2);roleRepository.save(role);//新增角色的同时新增关联的用户}//级联删除@Testpublic void testDelete() {//测试级联删除//先使用getOne方法获取到Role的引用，然后调用delete方法删除Role role = roleRepository.getOne(9L);roleRepository.delete(role);}@Testpublic void testsGet(){//测试按主键查询角色,输出关联角色数量Role role=roleRepository.findById(2L).get();System.out.println("roleName "+role.getRoleName());System.out.println("users.size "+role.getUsers().size());}// @Test
// public void testGet(){//测试按注解查询用户,关联获得
// User user=userRepository.findById(2L).get();
// System.out.println("usrName "+user.getUsrName());
// System.out.println("roleName "+user.getRole().getRoleName());
// }// @Resource// private UserService userService;// @Test
// public void testInsert(){
// User user = new User("JPA","123456",2L,1);
// userRepository.save(user);
// }
//
// @Test
// public void testGet(){
// User user = userRepository.findById(6L).get();
// System.out.println("usrName："+user.getUsrName());
// }
//
// @Test
// public void testFindByUsrNameLike(){
// List<User> list = userRepository.findByUsrNameLike("%s%");
// if (list != null){
// for (User user : list){
// System.out.println("usrName："+user.getUsrName());
// }
// }
// }
//
//
//
// @Test
// public void testFindPageByUsrRoleId(){
// int page=0,size=4;
// Sort sort = Sort.by(Sort.Direction.DESC,"usrId");
// Pageable pageable = PageRequest.of(page,size,sort);
// Page<User> userPage = userRepository.findPageByUsrRoleId(9L,pageable);
// System.out.println("总记录数："+userPage.getTotalElements());
// System.out.println("总页数："+userPage.getTotalPages());
// System.out.println("当前页数："+userPage.getNumber()+1);
// System.out.println("每页记录数："+userPage.getSize());
// System.out.println("当前页记录数："+userPage.getNumberOfElements());
// for (User user : userPage.getContent()){
// System.out.println("usrId："+user.getUsrId());
// }
// }
//
//
//
//
// @Test
// public void testFindPageByMap(){
// int page=0,size=5;
// Sort sort = Sort.by(Sort.Direction.DESC,"usrId");
// Pageable pageable = PageRequest.of(page,size,sort);
// Map param = new HashMap();
// param.put("roleId",3L);
// Page<User> userPager = userService.findPageByMap(param,pageable);
// System.out.println("总记录数 -----> "+userPager.getTotalElements());
// System.out.println("总页数 -----> "+userPager.getTotalPages());
// System.out.println("当前页数-----> "+userPager.getNumber());
// System.out.println("当前记录数 -----> "+userPager.getSize());
// System.out.println("当前页记录 -----> ");
// for (User user : userPager.getContent()){
// System.out.println("usrId："+user.getUsrId());
// }
// }
}总结
简化开发：减少了大量的 SQL 编写工作，通过对象操作数据库。
可维护性高：代码更加清晰、易于理解和维护。
数据库无关性：可以在不同的数据库之间轻松切换，只需更改配置。
强大的查询功能：支持方法命名查询和使用 JPQL（Java Persistence Query Language）进行复杂查询。