SpringBoot集成JPA

新建项目，添加依赖

 <!-- Spring Boot 集成jap依赖坐标-->
<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-data-jpa</artifactId>
  </dependency>
  <!-- Mysql数据库连接依赖坐标-->
  <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.47</version>
  </dependency>

项目配置

在application.properties文件中做以下配置

#通用数据源配置
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/springbootjpa
spring.datasource.username=root
spring.datasource.password=root

# JPA 相关配置
    #配置是否显示出响应执行sql语句
spring.jpa.show-sql=true
  #配置指明在程序启动的时候要检查数据库没有对应表创建，有表更新
spring.jpa.hibernate.ddl-auto=update

创建实体类，映射

import javax.persistence.*;

@Entity
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "stu_id")
    private Long stuId;
    @Column(name = "stu_name")
    private String stuName;
    @Column(name = "stu_age")
    private int age;

    public Long getStuId() {
        return stuId;
    }

    public void setStuId(Long stuId) {
        this.stuId = stuId;
    }

    public String getStuName() {
        return stuName;
    }

    public void setStuName(String stuName) {
        this.stuName = stuName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "stuId=" + stuId +
                ", stuName='" + stuName + '\'' +
                ", age=" + age +
                '}';
    }
}

创建持久层接口

public interface StuRepository extends JpaRepository<Student,Long>, JpaSpecificationExecutor<Student> {
}

测试

增

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringdatajpabootApplicationTests {
    @Autowired
    private StuRepository stuRepository;
   
    /**
     * 增
     * 创建一个实体类student添加到数据库
     */
    @Test
    public void addStudent() {
        Student student = new Student();
        student.setStuName("李白");
        student.setAge(22);
        stuRepository.save(student);
    }
}

数据库执行语句

//因为第一次测试，数据库中并没有我们的表student，所以会创建一个数据表student
Hibernate: create table student (stu_id bigint not null auto_increment, stu_age integer, stu_name varchar(255), primary key (stu_id)) engine=MyISAM
Hibernate: insert into student (stu_age, stu_name) values (?, ?)

我们的数据库中就新增了一条数据

改

/**
 * 改
 */
@Test
public void updateStudent() {
    Student student = new Student();
    student.setStuId(1L);
    student.setStuName("兰陵王");
    student.setAge(23);
    stuRepository.save(student);

    Student student2 = new Student();
    student2.setStuId(5L);
    student2.setStuName("赵云");
    student2.setAge(21);
    stuRepository.save(student2);
}

我们来看一下数据库执行语句：

Hibernate: select student0_.stu_id as stu_id1_0_0_, student0_.stu_age as stu_age2_0_0_, student0_.stu_name as stu_name3_0_0_ from student student0_ where student0_.stu_id=?
Hibernate: update student set stu_age=?, stu_name=? where stu_id=?
Hibernate: select student0_.stu_id as stu_id1_0_0_, student0_.stu_age as stu_age2_0_0_, student0_.stu_name as stu_name3_0_0_ from student student0_ where student0_.stu_id=?
Hibernate: insert into student (stu_age, stu_name) values (?, ?)

我们会发现数据库竟然执行了一次两次select，一次update和一次insert，这是因为save(Object object)方法会先执行select语句检查我们的数据表中是否存在有相应id的数据，如果存在，则执行update操作，否则执行insert操作。

我们执行后的数据表为：

删

    /**
     * 删
     */
     @Test
    public void deleteStudent(){
        stuRepository.deleteById(1L);
    }

数据库执行语句：

Hibernate: select student0_.stu_id as stu_id1_0_0_, student0_.stu_age as stu_age2_0_0_, student0_.stu_name as stu_name3_0_0_ from student student0_ where student0_.stu_id=?
Hibernate: delete from student where stu_id=?

执行后数据库表：

查

在测试之前，我们先向数据库中添加几条数据：

    @Test
    public void addStudent2() {
        Student student = new Student();
        student.setStuName("孙悟空");
        student.setAge(23);
        stuRepository.save(student);

        Student student2 = new Student();
        student2.setStuName("庄周");
        student2.setAge(21);
        stuRepository.save(student2);

        Student student3 = new Student();
        student3.setStuName("夏侯惇");
        student3.setAge(21);
        stuRepository.save(student3);
    }

findById

顾名思义，根据ID进行查询

    /**
     * 查
     * findById
     */
    @Test
    public void findOne(){
        Optional<Student> student = stuRepository.findById(3L);
        System.out.println(student.toString());
    }

执行数据库语句：

Hibernate: select student0_.stu_id as stu_id1_0_0_, student0_.stu_age as stu_age2_0_0_, student0_.stu_name as stu_name3_0_0_ from student student0_ where student0_.stu_id=?

执行输出结果：

Optional[Student{stuId=3, stuName='孙悟空', age=23}]

findAll

顾名思义，查询全部

    /**
     * 查
     * findAll
     */
    @Test
    public void findAll(){
        List<Student> students = stuRepository.findAll();
        students.forEach(a->System.out.println(a.toString()));
    }

数据库执行语句：

Hibernate: select student0_.stu_id as stu_id1_0_, student0_.stu_age as stu_age2_0_, student0_.stu_name as stu_name3_0_ from student student0_

执行输出结果：

Student{stuId=3, stuName='孙悟空', age=23}
Student{stuId=2, stuName='赵云', age=21}
Student{stuId=4, stuName='庄周', age=21}
Student{stuId=5, stuName='夏侯惇', age=21}