jpa入门demo

表结构：

SQL脚本如下：

/*
 Navicat Premium Data Transfer

 Source Server         : li
 Source Server Type    : MySQL
 Source Server Version : 50037
 Source Host           : localhost:3306
 Source Schema         : test

 Target Server Type    : MySQL
 Target Server Version : 50037
 File Encoding         : 65001

 Date: 30/07/2019 09:35:17
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for sys_user
-- ----------------------------
DROP TABLE IF EXISTS `sys_user`;
CREATE TABLE `sys_user`  (
  `id` bigint(20) NOT NULL DEFAULT '',
  `password` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `username` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  PRIMARY KEY USING BTREE (`id`)
) ENGINE = MyISAM CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of sys_user
-- ----------------------------
INSERT INTO `sys_user` VALUES (1, 'root', 'root');
INSERT INTO `sys_user` VALUES (2, 'sang', 'sang');

SET FOREIGN_KEY_CHECKS = 1;

开始创建项目：
添加如下依赖：

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
            <version>5.1.14</version>
        </dependency>

application.yml配置文件如下：

datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/test?characterEncoding=utf-8
    username: root
    password: admin

项目目录结构：

创建User实体类：
@Table注解中的表明要和数据库中的表明一样。

@Entity
@Table(name = "sys_user")
public class User{
    @Id
    @GeneratedValue
    private long id;
    @Column(length = 25)
    private String username;
    @Column(length = 15)
    private String password;

    public long getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

自定义Repository类：

public interface UserResposity  extends JpaRepository<User,Integer> {
    User findAllByUsername(String username);

    User findById(Long id);

}

创建一个controller：

@RestController
public class UserController {
    @Autowired
    UserResposity userResposity;
    @GetMapping("/ss")
    public User ss(String username){
        return  userResposity.findAllByUsername(username);
    }

    @GetMapping("/findById")
    public User findById(Long id){
        return userResposity.findById(id);
    }
}