springboot-5-持久层技术

整合mybatis

流程：

导入依赖：

除了mybaits还有mysql和jdbc依赖

<!--mybatis-->
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>1.3.2</version>
</dependency>
<!--mysql-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>
<!--druid-->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.21</version>
</dependency>

配置数据源信息（两个选择），前者为jdbc数据源，后者为druid数据源

spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.url=jdbc:mysql://localhost:3306/ssm_crud
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
---------------------------
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.url=jdbc:mysql://localhost:3306/ssm_crud
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource

还要配置一些mybaits的基本配置，比如：

• 别名配置
• mapper的xml文件位置
• 其他

mybatis.type-aliases-package=com.wang.pojo
# mybatis.mapper-locations=classpath:mapper/*.xml

写好pojo类，后面些数据访问层需要用

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {
    private Integer employeeId;
    private String employeeName;
    private String gender;
    private String email;
    private Department department;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Department {
    private Integer departmentId;
    private String departmentName;
}

在dao包下写好mapper接口

@Mapper		//或者在主程序下添加@MapperScan("包位置")
@Repository
public interface EmployeeMapper {

    //查询全部员工
    List<Employee> getAllEmployee();

    //通过id查找员工
    Employee getEmployeeById(Integer id);

    //添加员工
    Integer addEmployee(Employee employee);

    //更新员工
    Integer updateEmployee(Employee employee);

    //删除员工
    Integer deleteEmployee(Integer id);
}

mapper接口对应的xml配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wang.dao.DepartmentMapper">
    <resultMap id="departmentMap" type="department">
        <id column="department_id" property="departmentId"/>
        <result column="department_name" property="departmentName"/>
    </resultMap>

    <!--查询全部department-->
    <!--List<Department> getAllDepartment();-->
    <select id="getAllDepartment" resultMap="departmentMap">
        select * from tbl_department
    </select>

    <!--查询特定id的department-->
    <!--Department getDepartmentById(Integer id);-->
    <select id="getDepartmentById" resultMap="departmentMap">
        select * from tbl_department where department_id = #{id}
    </select>
</mapper>

测试使用：

@SpringBootTest
public class Test {

    @Autowired
    DepartmentMapper departmentMapper;

    @org.junit.jupiter.api.Test
    public void test(){
        System.out.println(departmentMapper.selectByPrimaryKey(1));
    }
}

多数据源开发:

怎么让springboot知道这个是一个mybatis下的mapper接口？

• 在mapper上加上@Mapper

  @Mapper
  public interface UseMapper {
  }
  

• 在主程序上加上@MapperScan("mapper接口放置的包")
  
  在这样spring就会直接去扫描这个包下的接口作为mapper

mapper接口需要放到IOC容器中去，故需要加上@Repository

测试数据库连接是否成功

@SpringBootTest
class DemoApplicationTests {

    @Autowired
    DataSource dataSource;

    @Test
    void contextLoads() throws SQLException {
        System.out.println(dataSource.getConnection());
    }

}

常见错误：

1、用#{参数}查找时#和{参数}中间不要有空格

2、Invalid bound statement (not found): com.wang.dao.EmployeeDao.queryEmployee表示找不到Mapper对应的xml文件

3、@Repository注解在mapper接口上可有可无，但在一些地方会报错