Spring Boot整合Mybatis Plus

本文将以最简单的方式带你学会Spring Boot整合Mybatis Plus实现基本的CRUD，冲冲冲！

一、简单介绍

Mybatis Plus，简称MP，官网https://mp.baomidou.com/

​​在MyBatis 的基础上只做增强不做改变，为简化开发、提高效率而生。​​

​​意愿​​​：成为 MyBatis 最好的搭档，就像 ​​魂斗罗​​ 中的 1P、2P，基友搭配，效率翻倍。

二、环境准备和基本配置

1.创建Spring Boot项目，引入依赖

<!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!-- 整合mybatis plus-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.2.0</version>
        </dependency>
        <!-- 数据库连接池-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.9</version>
        </dependency>
        <!--  test依赖-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

2.修改配置文件

server:
  port: 8099
spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    username: root
    password: 12345
    url: jdbc:mysql://127.0.0.1:3306/test
    type: com.alibaba.druid.pool.DruidDataSource

3.数据库准备

CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

4.项目结构和实体类准备

实体类：

public class Student {

    private Integer id;

    private String name;

    private Integer age;
    
    //构造方法......
    //Getter、Setter......
}

三、CRUD操作

1.继承BaseMapper

首先将Mapper层的接口集成BaseMapper,其中​​T就是需要操作的实体类泛型​​。

@Mapper
@Repository
public interface StudentMapper extends BaseMapper<Student> {
}

2.创建Service层接口和实现类

接口

public interface StudentService {

    /**
     * 保存Student
     *
     * @param student
     * @return
     */
    int saveStudent(Student student);

    /**
     * 根据id查找
     *
     * @param id
     * @return
     */
    Student findStudentById(int id);

    /**
     * 查找全部
     *
     * @return
     */
    List<Student> fingAllStudnet();

    /**
     * 删除一个
     *
     * @param id
     * @return
     */
    int deleteStudentById(int id);

    /**
     * 修改一个
     *
     * @param student
     * @return
     */
    int updateStudentById(Student student);

    /**
     * 根据姓模糊查询
     *
     * @param firstName
     * @return
     */
    List<Student> findStudentByFirstName(Student firstName);

}

实现类

@Service
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Override
    public int saveStudent(Student student) {
        return 0;
    }

    @Override
    public Student findStudentById(int id) {
        return null;
    }

    @Override
    public List<Student> findAllStudent() {
        return null;
    }

    @Override
    public int deleteStudentById(int id) {
        return 0;
    }

    @Override
    public int updateStudentById(Student student) {
        return 0;
    }

    @Override
    public List<Student> findStudentByFirstName(String firstName) {
        return null;
    }
}

3.方法的实现

下面我们来一一的实现这些方法

（1）保存一个

@Override
public int saveStudent(Student student) {
    return studentMapper.insert(student);
}

测试：

@Autowired
private StudentService studentService;

@Test
void testSaveStudent() {
    Student student = new Student(1,"张三", 23);
    System.out.println(studentService.saveStudent(student));
}

结果：

（2）根据id查找

@Override
public Student findStudentById(int id) {
    QueryWrapper<Student> wrapper = new QueryWrapper<>();
    wrapper.eq("id", id);
    return studentMapper.selectOne(wrapper);
}

测试

@Test
void testFindStuById() {
    System.out.println(studentService.findStudentById(1));
}

结果：

（3）查找全部

在查找全部之前我们先多插入一点

@Override
public List<Student> findAllStudent() {
    return studentMapper.selectList(new QueryWrapper<>());
}

测试

@Test
void testFindAllStu(){
    System.out.println(studentService.findAllStudent());
}

结果：

（4）删除一个

@Override
public int deleteStudentById(int id) {
    return studentMapper.deleteById(id);
}

测试

@Test
void testRemoveStudent(){
    System.out.println(studentService.deleteStudentById(1));
}

结果

（5）修改一个

@Override
public int updateStudentById(Student student) {
    return studentMapper.updateById(student);
}

测试

@Test
void testUpdateStu(){
    System.out.println(studentService.updateStudentById(new Student(2,"张小四",200)));
}

结果

（6）根据姓模糊查询

找出全部姓张的人

@Override
public List<Student> findStudentByFirstName(String firstName) {
    QueryWrapper<Student> wrapper = new QueryWrapper<>();
    wrapper.likeRight("name", firstName);
    return studentMapper.selectList(wrapper);
}

测试

@Test
void testLikeFind(){
    System.out.println(studentService.findStudentByFirstName("张"));
}

结果

四、可能遇到的问题

1.让主键自增

@TableId(type = IdType.AUTO)
private Integer id;

2.实体类和表名不一致

//@TableName("数据库表名")
@TableName("student")

3.实体类属性和表的字段名不一致

@TableId(value = "id", type = IdType.AUTO)
private Integer id;

@TableField("name")
private String name;

@TableField("age")
private Integer age;

4.插入数据后让自增id回写(很实用)

@TableId(value = "id", type = IdType.AUTO)  //只能有一个@TableId
private Integer id;

@TableField("name")
private String name;

@TableField("age")
private Integer age;

测试下：

// Service
@Override
public int saveStudent(Student student) {
    int result = studentMapper.insert(student);
    System.out.println(student);
    return result;
}
//  Test  //
@Test
void testSaveStudent() {
    Student student = new Student( "张四", 23);
    System.out.println(studentService.saveStudent(student));
}