springBoot学习（二）：初学JPA

　　依旧跟着大佬学习JPA，在这里记下过程。

　　JPA主要做的事情是简化数据库操作，至少现在为止，我觉得还是挺方便简单明了的。在原本代码中，更改UserController、User、UserRepository，删除UserRepositoryImpl

如何使用JPA

1、创建实体类

　　将User改成实体类，每一个User实例相当于数据库表格的一行。这个User类是最简单的那种，只包含了几个属性以及各个属性必须的getter和setter方法，其中id是自增的主键，不包含各种映射关系。

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity //实体
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)//自增长策略
    private Long id;//唯一标识
    private  String name;
    private  Integer age;

    protected User() {//无参默认构造器
    }

    public User(Long id, String name, Integer age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

User

2、修改资源库

import com.example.demo.domain.User;
import org.springframework.data.repository.CrudRepository;

import java.util.List;

public interface UserRepository extends CrudRepository<User , Long> {

}

UserRepository

同时删除原本的UserRepositoryImpl 类

在不考虑复杂的数据处理的情况下，从CrudRepository继承的方法已经足够使用

3、修改controller

import com.example.demo.domain.User;
import com.example.demo.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.ModelAndView;

import java.util.Optional;

@RestController
@RequestMapping("/user")
public class UserController {

    @Autowired
    private UserRepository userRepository;

    //查词所有用户
    @GetMapping("/userlist")
    public ModelAndView userList(Model model){
        model.addAttribute("userList",userRepository.findAll());
        model.addAttribute("title","用户管理");
        return  new ModelAndView("user/list","userModel",model);
    }
    //根据id 查询用户
    @GetMapping("{id}")
    public ModelAndView view(@PathVariable("id") Long id, Model model){
        Optional<User> user= userRepository.findById(id);
        model.addAttribute("user",user.get());
        model.addAttribute("title","查看用户");
        return new ModelAndView("user/view" ,"userModel",model);
    }

    //获取创建表单页面
    @GetMapping("/form")
    public ModelAndView createForm(Model model){
        model.addAttribute("user",new User(null,null,null));
        model.addAttribute("title","创建用户");
        return new ModelAndView("user/form","userModel",model);
    }

    //保存用户
    @PostMapping
    public ModelAndView saveOrUpdateUser(User user){
        user =userRepository.save(user);
        return new ModelAndView("redirect:/user/userlist");
    }

    //根据id删除用户
    @GetMapping(value = "delete/{id}")
    public ModelAndView delete(@PathVariable("id") Long id){
        userRepository.deleteById(id);
        return new ModelAndView("redirect:/user/userlist");
    }

    //修改用户界面
    @GetMapping(value = "edit/{id}")
    public ModelAndView editForm(@PathVariable("id") Long id,Model model){
        Optional<User> user =userRepository.findById(id);
        model.addAttribute("user",user);
        model.addAttribute("title","编辑用户");
        return new ModelAndView("user/form" ,"userModel",model);
    }
}

UserController