一个简单jpa例子

package com.example.demo.entity;

import javax.persistence.*;

/*使用jpa注解配置映射关系*/
/*告诉jpa这是一个实体类和（数据表映射的类）*/
@Entity
@Table(name = "tal_user")
public class User {
    @Id /*这是主键*/
    @GeneratedValue(strategy = GenerationType.IDENTITY) /*主键自增*/
    private Integer id;
    @Column(name = "lastName",length = 50)/*这是和数据表对应的一个列*/
    private String lastName;
    @Column  /*省略就代表默认属性名就是列名*/
    private String email;

    public Integer getId() {
        return id;
    }

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

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

package com.example.demo.repository;

import com.example.demo.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
/*继承jpaRepository来完成对数据库的操作 参数是实体类型和实体类中的Id类型*/
public interface UserRepository extends JpaRepository<User, Integer> {

}

package com.example.demo.Controller;

import com.example.demo.entity.User;
import com.example.demo.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;


@RestController
public class UserController {
    @Autowired
    UserRepository userRepository;
    @GetMapping("/user/{id}")
    public List<User> getUser(@PathVariable("id") Integer id){
        User user = userRepository.getOne(id);

        final List<User> users = userRepository.findAll();
        return users;
    }
    @GetMapping("/user")
    public User insertUser(User user){
        User save = userRepository.save(user);
        return save;
    }

}

spring:
  datasource:
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/jpa?serverTimezone=UTC
    driver-class-name: com.mysql.cj.jdbc.Driver
  jpa:
    hibernate:
#      更新或者创建表结构
      ddl-auto: update
#      控制台显示sql
    show-sql: true

  <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>8.0.12</scope>
        </dependency>