<!-- spring jpa -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.20</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

package com.demo.springboot.entity;
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import lombok.Data;
import javax.persistence.*;
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@Data
@Entity                     //告诉JPA这是一个实体类（和数据表映射的类）
@Table(name = "t_user")     //@Table来指定和哪个数据表对应;如果省略默认表名就是user；
public class User {
    @Id                                                 //这是一个主键
    @GeneratedValue(strategy = GenerationType.IDENTITY) //自增主键
    private Integer id;
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    @Column(name = "last_name", length = 50)            //这是和数据表对应的一个列
    private String lastName;
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    @Column                                             //省略默认列名就是属性名
    private String email;
}

package com.demo.springboot.repository;
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import com.demo.springboot.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
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/**
 * 继承JpaRepository来完成对数据库的操作
 * JpaRepository 继承了CrudRepository、PagingAndSortingRepository、QueryByExampleExecutor
 * 实现了常用的增删改查、分页、排序等功能
 */
public interface UserRepository extends JpaRepository<User, Integer> {
    User findByLastName(String lastName);  // 根据JPA命名规则，不需要实现即可使用
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    User findByEmail(String email);
}

package com.demo.springboot.controller;
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import com.demo.springboot.entity.User;
import com.demo.springboot.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.PostMapping;
import org.springframework.web.bind.annotation.RestController;
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@RestController
public class UserController {
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    @Autowired
    UserRepository userRepository;
    
    @PostMapping("/user")
    public User insertUser(User user) {
        // 使用save方法进行新增
        User save = userRepository.save(user);
        return save;
    }
    
    @GetMapping("/user/id/{id}")
    public User getUser(@PathVariable("id") Integer id) {
        User user = userRepository.findOne(id);
        return user;
    }
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    @GetMapping("/user/name/{lastName}")
    public User getUserByLastName(@PathVariable("lastName") String lastName) {
        // 调用自定义的findByLastName接口，不需要自己实现
        User user = userRepository.findByLastName(lastName);
        return user;
    }
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    @GetMapping("/user/email/{email}")
    public User getUserByEmail(@PathVariable("email") String email) {
        User user = userRepository.findByEmail(email);
        return user;
    }
}