Day24——MyBatis自定义映射 collection 分步查询使用延迟加载

悠悠 2023-07-04 14:11 32阅读 0赞

# 一. 例子 #

DepartmentMapperResultMap.java

package com.atguigu.mybatis.dao;
    
    import com.atguigu.mybatis.beans.Department;
    
    public interface DepartmentMapperResultMap { 
    	
    	public Department selectDepartmentAndEmployeesStep(Integer id);
    }

EmployeeMapperResultMap.java

package com.atguigu.mybatis.dao;
    
    import java.util.List;
    
    import com.atguigu.mybatis.beans.Employee;
    
    public interface EmployeeMapperResultMap { 
    
    	public List<Employee> selectEmployeesByDid(Integer did);
    }

EmployeeMapperResultMap.xml

<select id="selectEmployeesByDid" resultType="com.atguigu.mybatis.beans.Employee">
             select id, last_name, email, gender from tbl_employee where d_id = #{did}	
    	</select>

DepartmentMapperResultMap.xml

<select id="selectDepartmentAndEmployeesStep" resultMap="myDeptAndEmpsStep">
    	     select id, dept_name from tbl_dept where id = #{id}
    	</select>
    	<resultMap type="com.atguigu.mybatis.beans.Department" id="myDeptAndEmpsStep">
    	     <id column="id" property="id"/>
    	     <result column="dept_name" property="departmentName"/>
    	     
    	     <collection property="emps" select="com.atguigu.mybatis.dao.EmployeeMapperResultMap.selectEmployeesByDid" column="id">
    	     </collection>
    	</resultMap>

TestMyBatisResultMap.java

@Test
    	public void testResultMapCollectionStep() throws Exception { 
    		SqlSessionFactory ssf = getSqlSessionFactory();
    		SqlSession session = ssf.openSession();
    		
    		try { 
                  DepartmentMapperResultMap mapper = 
                		  session.getMapper(DepartmentMapperResultMap.class);			
                  Department dept = mapper.selectDepartmentAndEmployeesStep(1);
                  System.out.println(dept.getDepartmentName());
                  System.out.println("------------------------------------");
                  
                  System.out.println(dept.getEmps());
    			
    			session.commit();
    		} finally { 
    			// TODO: handle finally clause
    			session.close();
    		}
    	}
    
    public SqlSessionFactory getSqlSessionFactory() throws Exception { 
    		String resource = "mybatis-config.xml"; 
    		InputStream inputStream = 
    				Resources.getResourceAsStream(resource); 
    		SqlSessionFactory sqlSessionFactory = 
    				new SqlSessionFactoryBuilder().build(inputStream);
    		return sqlSessionFactory;
    	}