原理等不在赘述，这里主要通过代码展现。
在mybatis（一）基础上，新建一个dao包，并在里面编写接口，然后再在xml文件中引入接口路径，其他不变，在运用阶段将比原始方法更节约时间，因为不用再去手动的
引用sql,我们只需调用dao层的方法，然后让dao层的方法去找配置文件，去找sql，sql查询数据并赋值给对象，或者设置对象参数值在经过sql更新到数据库，小伙伴们这就是
orm对象关系映射模型！（个人见解，不对之处请指正。）
新增后项目：
一、新建一个com.ckx.dao包，并new一个（interface）DeptDao.java。
DeptDao.java：
package com.ckx.dao;import java.util.List;import org.apache.ibatis.annotations.Param;import com.ckx.entity.Dept;public interface DeptDao {//通过ID查数据public Dept selectDeptById(int deptno);//查询一个结果集public List<Dept> selectDeptAll();//多条件动态 ，查询注意@Param的重要性，没有回报参数not find错误public List<Dept> selectDeptByMore(@Param("deptno") int deptno,@Param("dname") String dname);//根据ID动态修改public int updateDeptById(Dept d);//批量删除public int deleteDepts(List<Integer> list);//新增public int insertDept(Dept d); public int insertDept2(Dept d); //多表关联public Dept selectDeptEmps(int t);}
二、配置Dept.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"> <!--接口编程--> <mapper namespace="com.ckx.dao.DeptDao"><resultMap type="Dept" id="DeptList"><result column="deptno" property="deptno"/><result column="dname" property="dname"/><result column="loc" property="loc"/><!-- 代表集合数据 property：实体bean中的属性名称 ofType：数据类型 --><collection property="emps" ofType="Emp"><result column="EMPNO" property="empno" /><result column="ENAME" property="ename" /><result column="JOB" property="job" /><result column="MGR" property="mgr" /><result column="HIREDATE" property="hiredate" /><result column="SAL" property="sal" /><result column="COMM" property="comm" /><result column="DEPNO" property="depno" /></collection></resultMap> <!-- 通过ID查询--><select id="selectDeptById" parameterType="int" resultType="Dept">select * from dept where deptno = #{deptno}</select> <!-- 查询整张表，注意返回参数是一个DeptList集合，这个需要在上面配置--><select id="selectDeptAll" resultMap="DeptList">select * from dept </select> <!-- 多参数动态查询--><select id="selectDeptByMore" resultMap="DeptList">select * from dept <where><if test="deptno != 0">deptno = #{deptno}</if><if test="dname != null">or dname like #{dname}</if></where></select> <!-- 动态更新数据--><update id="updateDeptById" parameterType="Dept">update dept <set><if test="deptno != null">dname = #{dname},</if><if test="deptno != null">loc = #{loc}</if></set>where deptno = #{deptno}</update> <!-- 批量删除--><delete id="deleteDepts" parameterType="list">delete from dept where deptno in<foreach item="item" index="index" collection="list" open="("separator=", " close=") ">#{item}</foreach></delete> <!-- 新增数据--><insert id="insertDept" parameterType="Dept" >insert into dept (deptno,dname,loc) values (#{deptno},#{dname},#{loc})</insert> <!-- 连表查询，注意1、到层返回值为对象类本身 2、查询返回值为list集合。--><select id="selectDeptEmps" parameterType="int" resultMap="DeptList">SELECT d.DNAME,e.* FROM dept d,emp e WHERE d.DEPTNO=e.DEPNO and d.DEPTNO = #{deptno}</select><!-- 未完成--><sql id='dept'>TEST_USER</sql><!-- 注意这里需要先查询自增主键值 --><insert id="insertDept2" parameterType="Dept"><selectKey keyProperty="deptno" resultType="int" order="BEFORE">SELECT LAST_INSERT_deptno()</selectKey>insert into <include refid="dept" /> (deptno,dname,loc)values ( #{deptno},#{dname},#{loc} )</insert></mapper>
三、测试
DeptTest.java：
package com.ckx.test;import java.io.IOException; import java.io.Reader; import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; import java.util.ListIterator;import javax.mail.Session;import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.ckx.dao.DeptDao; import com.ckx.entity.Dept; import com.ckx.entity.Emp;public class DeptTest {static SqlSessionFactory sessionFactory;static Reader reader;static SqlSession sqlSession;static {try {reader = Resources.getResourceAsReader("config.xml");sessionFactory = new SqlSessionFactoryBuilder().build(reader);sqlSession = sessionFactory.openSession();} catch (IOException e) {// TODO Auto-generated catch block e.printStackTrace();}}public void select(){DeptDao dao = sqlSession.getMapper(DeptDao.class);Dept d = dao.selectDeptById(10);System.out.println(d.getDname());}public void selectDeptAll(){DeptDao dao = sqlSession.getMapper(DeptDao.class);List<Dept> list = dao.selectDeptAll();for (Dept dept : list) {String s = dept.getDname();System.out.println(s);}Iterator<Dept> ite = list.iterator();while (ite.hasNext()) {Dept d = ite.next();String ss = d.getLoc();System.out.println(ss);}for (int i = 0; i < list.size(); i++) {Dept d = list.get(i);int t = d.getDeptno();System.out.println(t);}}public void selectDeptByMore(){DeptDao dao = sqlSession.getMapper(DeptDao.class);List<Dept> list = dao.selectDeptByMore(20,"A%");Iterator<Dept> it = list.iterator();while (it.hasNext()) {Dept dept = (Dept) it.next();String s = dept.getDname();System.out.println(s);}}public void updateDeptById(){DeptDao dao = sqlSession.getMapper(DeptDao.class);Dept d = new Dept();d.setDeptno(10);d.setDname("ASC");d.setLoc("desc");dao.updateDeptById(d);System.out.println(d.getDeptno()+d.getDname()+d.getLoc());sqlSession.commit();}public void deleteDepts(){DeptDao dao = sqlSession.getMapper(DeptDao.class);List<Integer> list = new ArrayList<Integer>();list.add(0);dao.deleteDepts(list);}public void insertDept(){DeptDao dao = sqlSession.getMapper(DeptDao.class);Dept d = new Dept();d.setDeptno(10);d.setDname("assc");d.setLoc("deff");dao.insertDept(d);sqlSession.commit();}//多表联查public void selectDeptEmps(){DeptDao dao = sqlSession.getMapper(DeptDao.class);Dept d = dao.selectDeptEmps(10);List<Emp> list = d.getEmps();for (Emp emp : list) {String s = emp.getEname();System.out.println(d.getDname()+"\t"+s);}};//主键自增为完成public void insertDept2(){DeptDao dao = sqlSession.getMapper(DeptDao.class);Dept d = new Dept();d.setDname("sss");d.setLoc("ddd");dao.insertDept(d);sqlSession.commit();System.out.println(d.getDeptno());}public static void main(String[] args) {DeptTest dt = new DeptTest();dt.selectDeptEmps();} }
以上皆为测试过运行正常的方法，每一个方法的调用只需能改dt后的方法即可。
具体注意说明：
