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Mybatis的resultType与resultMap
resultType
指定一个JavaBean的全类名，mybatis会把查询到的结果自动封装为指定的JavaBean
<!-- Employee getEmpById(Integer id); -->
<select id="getEmpById" resultType="com.mxc.entity.Employee">
select id, last_name, gender, email from emp where id = #{id}
</select>
resultMap
resultMap用于自定义JavaBean的封装规则
<!--
type：指定自定义规则最终封装的目标Java类型
id:指定id，便于被其他select中的resultMap使用
-->
<resultMap type="com.mxc.bean.Employee" id="rmDemo">
<!-- 指定主键列的封装规则
id：定义主键，底层会有优化；
column：指定表的哪一列
property：指定对应的JavaBean的属性
-->
<id column="id" property="id"/>
<!-- 定义普通列封装规则 -->
<result column="last_name" property="lastName"/>
<result column="email" property="email"/>
<result column="gender" property="gender"/>
</resultMap>
<!-- resultMap:自定义结果集映射规则； -->
<!-- public Employee getEmpById(Integer id); -->
<select id="getEmpById" resultMap="rmDemo">
select * from employee where id=#{id}
</select>
两个典型的resultMap使用场景
JavaBean
-
Employee.javapackage com.mxc.entity; public class Employee { private Integer id; private String lastName; private String gender; private String email; private Department dept; public Employee() { } public Employee(Integer id, String lastName, String gender, String email) { this.id = id; this.lastName = lastName; this.gender = gender; this.email = email; } // 省略getter和setter... @Override public String toString() { return "Employee{" + "id=" + id + ", lastName='" + lastName + '\'' + ", gender='" + gender + '\'' + ", email='" + email + '\'' + '}'; } } -
Department.javapackage com.mxc.entity; import java.util.List; public class Department { private Integer id; private String deptName; private List<Employee> emps; public Department() { } public Department(Integer id, String deptName) { this.id = id; this.deptName = deptName; } // 省略getter和setter... @Override public String toString() { return "Department{" + "id=" + id + ", deptName='" + deptName + '\'' + '}'; } }
查询员工同时查询员工对应的部门
代码
-
EmployeeMapper.javaEmployee getEmpByIdAssociate(Integer id); -
EmployeeMapper.xml<resultMap id="empMap" type="com.mxc.entity.Employee"> <id column="id" property="id"></id> <result column="last_name" property="lastName"></result> <result column="gender" property="gender"></result> <result column="email" property="email"></result> <association property="dept" column="d_id" select="com.mxc.dao.DeptMapper.getDeptById"></association> </resultMap> <select id="getEmpByIdAssociate" resultMap="empMap"> select * from emp where id = #{id} </select> -
DeptMapper.javaDepartment getDeptById(Integer id); -
DeptMapper.xml<select id="getDeptById" resultType="com.mxc.entity.Department"> select id, dept_name from dept where id = #{id} </select>
执行及结果
/**
* 获取SqlSessionFactory对象
* @return
* @throws IOException
*/
private SqlSessionFactory getSqlSessionFactory() throws IOException {
return new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
}
@Test
public void testAssociate() throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
Employee empByIdAssociate = employeeMapper.getEmpByIdAssociate(3);
System.out.println(empByIdAssociate.getLastName());
System.out.println(empByIdAssociate.getDept().getDeptName());
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
} finally {
sqlSession.close();
}
}
控制台打印：
13:47:57.277 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - ==> Preparing: select * from emp where id = ?
13:47:57.406 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - ==> Parameters: 3(Integer)
13:47:57.458 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - ====> Preparing: select id, dept_name from dept where id = ?
13:47:57.459 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - ====> Parameters: 1(Integer)
13:47:57.463 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - <==== Total: 1
13:47:57.467 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - <== Total: 1
夏侯瑾轩
研发部
开启延迟加载
-
延迟加载：在需要使用部门属性的时候才发SQL去数据库查询对应的信息
-
开启延迟加载：mybatis配置文件中加入如下配置
<settings> <!-- 其他配置... --> <!-- lazyLoadingEnabled：延迟加载的全局开关。当开启时，所有关联对象都会延迟加载。特定关联关系中可通过设置fetchType属性来覆盖该项的开关状态。默认为false --> <setting name="lazyLoadingEnabled" value="true"/> <!-- aggressiveLazyLoading：当开启时，任何方法的调用都会加载该对象的所有属性。否则，每个属性会按需加载。大于3.4.1版本以后的mybatis默认为false，之前默认为true --> <setting name="aggressiveLazyLoading" value="false"/> </settings> -
执行结果：
13:58:25.545 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - ==> Preparing: select * from emp where id = ? 13:58:25.636 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - ==> Parameters: 3(Integer) 13:58:25.745 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpByIdAssociate - <== Total: 1 夏侯瑾轩 13:58:25.750 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - ==> Preparing: select id, dept_name from dept where id = ? 13:58:25.750 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - ==> Parameters: 1(Integer) 13:58:25.754 [main] DEBUG com.mxc.dao.DeptMapper.getDeptById - <== Total: 1 研发部
查部门的同时查该部门下所有的员工
代码
-
DeptMapper.javaDepartment getDeptByIdCollection(Integer id); -
DeptMapper.xml<resultMap id="deptMap" type="com.mxc.entity.Department"> <id column="id" property="id"></id> <result column="dept_name" property="deptName"></result> <collection property="emps" ofType="com.mxc.entity.Employee" column="id" select="com.mxc.dao.EmployeeMapper.getEmpByDeptId"> </collection> </resultMap> <select id="getDeptByIdCollection" resultMap="deptMap"> select id, dept_name from dept where id = #{id} </select> -
EmployeeMapper.javaList<Employee> getEmpsByDeptId(Integer deptId); -
EmployeeMapper.xml<select id="getEmpsByDeptId" resultType="com.mxc.entity.Employee"> select * from emp where d_id = #{deptId} </select>
执行及结果（延迟加载）
/**
* 获取SqlSessionFactory对象
* @return
* @throws IOException
*/
private SqlSessionFactory getSqlSessionFactory() throws IOException {
return new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));
}
@Test
public void testCollection() throws IOException {
SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
DeptMapper deptMapper = sqlSession.getMapper(DeptMapper.class);
Department deptByIdCollection = deptMapper.getDeptByIdCollection(1);
System.out.println(deptByIdCollection.getDeptName());
List<Employee> emps = deptByIdCollection.getEmps();
for (Employee emp : emps) {
System.out.println("emp = " + emp);
}
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
} finally {
sqlSession.close();
}
}
控制台输出：
15:17:59.458 [main] DEBUG com.mxc.dao.DeptMapper.getDeptByIdCollection - ==> Preparing: select id, dept_name from dept where id = ?
15:17:59.564 [main] DEBUG com.mxc.dao.DeptMapper.getDeptByIdCollection - ==> Parameters: 1(Integer)
15:17:59.698 [main] DEBUG com.mxc.dao.DeptMapper.getDeptByIdCollection - <== Total: 1
研发部
15:17:59.703 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpsByDeptId - ==> Preparing: select * from emp where d_id = ?
15:17:59.704 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpsByDeptId - ==> Parameters: 1(Integer)
15:17:59.709 [main] DEBUG com.mxc.dao.EmployeeMapper.getEmpsByDeptId - <== Total: 2
emp = Employee{id=3, lastName='夏侯瑾轩', gender='1', email='[email protected]'}
emp = Employee{id=4, lastName='瑕', gender='0', email='[email protected]'}