帮我使用mybatis写一个分步查询查询员工表和部门表

1. 创建 Employee 实体类和 Department 实体类，分别对应员工表和部门表的结构。

Employee.java

public class Employee {
    private int id;
    private String name;
    private int age;
    private int departmentId;
    // getter/setter 省略
}

Department.java

public class Department {
    private int id;
    private String name;
    // getter/setter 省略
}

2. 创建 EmployeeMapper 接口和 DepartmentMapper 接口，用于定义查询方法。

EmployeeMapper.java

public interface EmployeeMapper {
    // 根据员工 id 查询员工信息
    Employee selectEmployeeById(int id);
    // 根据部门 id 查询部门信息
    Department selectDepartmentById(int id);
}

DepartmentMapper.java

public interface DepartmentMapper {
    // 根据部门 id 查询部门信息
    Department selectDepartmentById(int id);
}

3. 创建 EmployeeMapper.xml 和 DepartmentMapper.xml 文件，用于实现查询方法。

EmployeeMapper.xml

<?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.example.mapper.EmployeeMapper">
    <select id="selectEmployeeById" parameterType="int" resultType="com.example.entity.Employee">
        SELECT * FROM employee WHERE id = #{id}
    </select>
    <select id="selectDepartmentById" parameterType="int" resultType="com.example.entity.Department">
        SELECT * FROM department WHERE id = #{id}
    </select>
</mapper>

DepartmentMapper.xml

<?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.example.mapper.DepartmentMapper">
    <select id="selectDepartmentById" parameterType="int" resultType="com.example.entity.Department">
        SELECT * FROM department WHERE id = #{id}
    </select>
</mapper>

4. 在配置文件中配置 mapper。

<configuration>
    <mappers>
        <mapper resource="com/example/mapper/EmployeeMapper.xml"/>
        <mapper resource="com/example/mapper/DepartmentMapper.xml"/>
    </mappers>
</configuration>

5. 在业务代码中使用分步查询。

@Autowired
private EmployeeMapper employeeMapper;

@Autowired
private DepartmentMapper departmentMapper;

public Employee getEmployeeById(int id) {
    Employee employee = employeeMapper.selectEmployeeById(id);
    Department department = departmentMapper.selectDepartmentById(employee.getDepartmentId());
    employee.setDepartment(department);
    return employee;
}

以上是使用 MyBatis 实现分步查询的步骤和代码示例，希望能对你有所帮助。