mybatis

Employemapper.xml文件中，注意的是返回的类型resultType也是实体类对象的

<!-- public List<Employe> getEmpsByLastNameLike(String lastName); --> <select id="getEmpsByLastNameLike" resultType="com.atguigu.mybatis.hello.Employe"> select * from tbl_employe where last_name like #{lastName} </select>

接口EmployeMapper

package com.atguigu.mybatis.dao; import java.util.LinkedList; import java.util.List; import java.util.Map; import org.apache.ibatis.annotations.Param; import com.atguigu.mybatis.hello.Employe; public interface EmployeMapper { public List<Employe> getEmpsByLastNameLike(String lastName); }

测试文件

@Test public void test3() throws Exception{ SqlSession opSession=SqlSessionFactoryji(); try { EmployeMapper employeMapper=opSession.getMapper(EmployeMapper.class); List<Employe> likEmployes=employeMapper.getEmpsByLastNameLike("%t%"); for (Employe employe : likEmployes) { System.out.println(employe); } } finally { opSession.close(); } }

实现效果，

select记录封装map

EmployMapper.java

package com.atguigu.mybatis.dao; import java.util.LinkedList; import java.util.List; import java.util.Map; import org.apache.ibatis.annotations.MapKey; import org.apache.ibatis.annotations.Param; import com.atguigu.mybatis.hello.Employe; public interface EmployeMapper { //多条记录封装一个Map<Integer,Employe>:键是这条记录的主键，指是记录封装后的javaBean //告诉mybatis封装这个map的时候用哪个属性作为map的key @MapKey("id") public Map<Integer, Employe> getEmpByLastNameLikeReturnMap(String lastName); }

EmployeMapper.xml配置文件

<!-- public Map<Integer, Employe> getEmpByLastNameLikeReturnMap(String lastName); --> <select id="getEmpByLastNameLikeReturnMap" resultType="com.atguigu.mybatis.hello.Employe"> select * from tbl_employe where last_name like #{lastName} </select>

`测试类：

@Test public void test3() throws Exception{ SqlSession opSession=SqlSessionFactoryji(); try { EmployeMapper employeMapper=opSession.getMapper(EmployeMapper.class); // Map<String, Object> eMaPMap=employeMapper.getEmpByIdReturnMap(1); // System.out.println(eMaPMap); Map<Integer, Employe> empMap= employeMapper.getEmpByLastNameLikeReturnMap("%t%"); System.out.println(empMap); } finally { opSession.close(); } }

运行效果，多个记录封装在map中

resultMap自定义结果映射规则，不需要驼峰的设置

EmployeMapper.java

package com.atguigu.mybatis.dao; import com.atguigu.mybatis.hello.Employe; public interface EmployeMapperPlus { public Employe getEmployebyid(Integer id); }

EmployeMapperPlus.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.atguigu.mybatis.dao.EmployeMapperPlus"> <!--自定义某个javaBean的封装规则 type:自定义规则的Java类型 id:唯一id方便引用 --> <resultMap type="com.atguigu.mybatis.hello.Employe" id="myEmp"> <!--指定主键列的封装规则 id定义主键底层有优化 column：指定哪一列 property:指定对应的javaBean属性 --> <id column="id" property="id"></id> <!--定义普通封装规则 --> <result column="last_name" property="lastName"/> <!--其他不指定的列会自动封装，但是我们写resultMap就最好把全部的映射规则都写上 --> <result column="gender" property="gender"/> <result column="email" property="email"></result> </resultMap> <select id="getEmployebyid" resultMap="myEmp"> select * from tbl_employe where id=#{id} </select> </mapper>

测试类

@Test public void test5() throws Exception{ SqlSession opSession=SqlSessionFactoryji(); try { EmployeMapperPlus employMapperPlus=opSession.getMapper(EmployeMapperPlus.class); Employe employe = employMapperPlus.getEmployebyid(1); System.out.println(employe); } finally { opSession.close(); } }

##########注意将配置文件EmployMapperPlus.xml 记得引入中mybatis-config.xml

级联dept表，按需查询

<?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.atguigu.mybatis.dao.EmployeMapperPlus"> <!--自定义某个javaBean的封装规则 type:自定义规则的Java类型 id:唯一id方便引用 --> <resultMap type="com.atguigu.mybatis.hello.Employe" id="myEmp"> <!--指定主键列的封装规则 id定义主键底层有优化 column：指定哪一列 property:指定对应的javaBean属性 --> <id column="id" property="id"></id> <!--定义普通封装规则 --> <result column="last_name" property="lastName"/> <!--其他不指定的列会自动封装，但是我们写resultMap就最好把全部的映射规则都写上 --> <result column="gender" property="gender"/> <result column="email" property="email"></result> </resultMap> <!-- <select id="getEmployebyid" resultMap="myEmp"> select * from tbl_employe where id=#{id} </select> --> <!-- 联合查询，级联属性封装结果集 --> <resultMap type="com.atguigu.mybatis.hello.Employe" id="MyDifEmp"> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <result column="gender" property="gender"/> <result column="email" property="email"/> <result column="id" property="dept.id"></result> <result column="dept_name" property="dept.deptName"></result> </resultMap> <!--使用association定义关联的单个对象的封装规则 --> <resultMap type="com.atguigu.mybatis.hello.Employe" id="MyDifEmp2"> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <result column="gender" property="gender"/> <result column="email" property="email"/> <!--association可以指定联合的javaBean对象 property="dept":指定哪个属性是联合的对象 javaType：指定这个属性对象的类型[不能省略] --> <association property="dept" javaType="com.atguigu.mybatis.hello.Dept"> <id column="id" property="id"/> <result column="dept_name" property="deptName"/> </association> </resultMap> <!-- 场景一： 查询Employe的同时查询员工对应的部门 Employe==Department 一个员工有与之对应的部门 id last_name gender d_id did dept_name --> <select id="getEmpandDept" resultMap="MyDifEmp2"> SELECT e.id, e.gender, e.last_name, e.email, d.id, d.dept_name FROM tbl_employe e, tbl_dept d WHERE e.dept_id=d.id and e.id=#{id} </select> <!--使用association进行分布查询： 1.先按照员工id查询员工信息 2.根据查询员工信息中的d_id去部门表查出部门信息 3.部门设置到员工中； --> <resultMap type="com.atguigu.mybatis.hello.Employe" id="myEmpBystep"> <id column="id" property="id"></id> <result column="last_name" property="lastName"/> <result column="gender" property="gender"/> <result column="email" property="email"/> <!-- association定义关联对象的封装规则 select:表明当前属性是调用select指定的方法查出结果 流程：使用select指定的方法（传入column指定的这列参数的值）查出对象，并封装给property--> <association property="dept" select="com.atguigu.mybatis.dao.DeptMapper.getDeptbyId" column="dept_id"> </association> </resultMap> <select id="getEmployebyid" resultMap="myEmpBystep"> select * from tbl_employe where id=#{id} </select> <!--可以使用延迟加载（懒加载）；（按需加载） Employ===dept, 我们每次查询Employe对象的时候，都将一起查询出来。 部门信息在我们使用的时候再去查询； 实现的方法是：分段查询的基础上加上两个配置 <setting name="lazyLoadingEnabled" value="true"/> 关联的这个值使用的时候延迟加载，默认为false <setting name="aggressiveLazyLoading" value="false" /> 开启每一个属性全部加载出来，禁用的话可以按需加载 --> </mapper>

测试类

@Test public void test6() throws Exception{ SqlSession opSession=SqlSessionFactoryji(); try { EmployeMapperPlus employeMapperPlus=opSession.getMapper(EmployeMapperPlus.class); Employe employe=employeMapperPlus.getEmployebyid(1); System.out.println(employe); System.out.println(employe.getDept()); } finally { opSession.close(); } }