一、字段名与属性名（数据库的名字）不一样怎么办？
方案一：在小配置中配置一个resultMapper
<!--方案一：resultMapper 字段名与属性名不一致 -->
<resultMap type="Student" id="StudentMapper">
<result column="stuname2" property="stuname"/>
</resultMap> <!-- 查询所有 -->
<select id="findAll" resultMap="StudentMapper">
select * from student
</select>
方案二：在小配置中的查询语句用as
<!-- 方案二：as别名的方式 -->
<select id="findAll" resultType="Student">
select stuname2 as stuname from student
</select>
二、Mapper动态代理剔除实现类
第一步改动的地方是小配置的<mapper namespace="cn.happy.dao.IStudentDAO">写到接口
<?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="cn.happy.dao.IStudentDAO"> <!-- 方案二：as别名的方式 -->
<select id="findAll" resultType="Student">
select stuname2 as stuname from student
</select> </mapper>
第二步是在测试类调用接口的时候用getMapper获取一个接口实现类
public class MyTest {
IStudentDAO dao;
@Before
public void initData() throws IOException{
SqlSession session = MybatisUtil.getSession();
//动态踢出实现类
//首先要改StudentDAO.xml改成<mapper namespace="cn.happy.dao.IStudentDAO">
dao=session.getMapper(IStudentDAO.class);
}
/**
* selectALl学生
* @throws IOException
*/
@Test
public void findAll() throws IOException{
List<Student> list = dao.findAll();
for (Student student : list) {
System.out.println(student.getStuname());
/*System.out.println(student.getStuage());*/
}
}
}
三、用Map集合取值和使用索引号
（一）用map集合获取值
1在接口IStudentDAO定制一个方法
//多条件查询封装成map
public List<Student> findStudentMore(Map<String, Object> map);
2在小配置中id=“findStudentMore”要和接口的方法法名要一样
<!-- 多条件查询-->
<select id="findStudentMore" resultType="Student">
<!-- mysql数据库 -->
<!-- select * from student where stuname like '%' #{stuname} '%' and stuage>#{stuage} -->
<!-- orcl数据库 -->
select * from student where stuname like '%'||#{stuname}||'%' and stuage>#{stuage}
</select>
3在测试类中
/**
* 多条件查询
* @throws IOException
*/ @Test
public void findStudentMore(){ Map<String, Object> maplist=new HashMap<String, Object>();
maplist.put("stuname", "123");
maplist.put("stuage", 11);
List<Student> list = dao.findStudentMore(maplist);
for (Student student : list) {
System.out.println(student.getStuname());
} }
（二）使用索引
1在接口IStudentDAO定制一个方法
//多条件查询引号
public List<Student> findStudentByCondition(String name,int age);
2在小配置中id=“findStudentMore”要和接口的方法法名要一样
<select id="findStudentByCondition" resultType="Student">
<!-- mysql数据库
select * from student where stuname like '%' #{} '%' and stuage>#{}
orcl数据库 -->
select * from student where stuname like '%'||#{}||'%' and stuage>#{} </select>
3在测试类中
@Test
public void findStudentByCondition() throws IOException{
String name="人";
int age=12;
List<Student> list = dao.findStudentByCondition(name,age);
for (Student student : list) {
System.out.println(student.getStuname());
} }
小总结：
四、智能标签
他们共同用到的是如下
1定义一个方法在接口中
public List<Student> findStudentByif(Student stu);
2测试类
public class MyTest {
IStudentDAO dao;
@Before
public void initData() throws IOException{
SqlSession session = MybatisUtil.getSession();
//动态踢出实现类
//首先要改StudentDAO.xml改成<mapper namespace="cn.happy.dao.IStudentDAO">
dao=session.getMapper(IStudentDAO.class);
}
/**
* 多条件查询
* @throws IOException
*/
@Test
public void findStudentByCondition() throws IOException{
String name="人";
int age=12;
Student stu=new Student();
stu.setStuage(age);
stu.setStuname(name);
List<Student> list = dao.findStudentByif(stu);
for (Student student : list) {
System.out.println(student.getStuname());
}
}
3在小配置中的配置
if标签
<!-- 多条件查询 -->
<select id="findStudentif" resultType="Student">
select * from student where = <if test="stuname!=null">
and stuname like '%'||#{stuname}||'%'
</if>
<if test="stuage!=null">
and stuage>#{stuage}
</if> </select>
where标签 注意如果有<where>标签就不需要where 1=1
<!-- 多条件查询 -->
<select id="findStudentBychoose" resultType="Student">
select * from student <!-- where =1如果有where标签就不需要 -->
<where>
<if test="stuname!=null">
and stuname like '%'||#{stuname}||'%'
</if>
<if test="stuage!=null">
and stuage>#{stuage}
</if>
</where>
</select>
choose标签
<!--多条件查询where = 如果有where标签就不需要-->
<select id="findStudentByif" resultType="Student">
select * from student
<where>
<choose>
<when test="stuname!=null">
and stuname like '%'||#{stuname}||'%' </when>
<otherwise>
</otherwise>
</choose> </where>
</select>
foreach标签
（一）数组
1在接口中
//查询是一个3,11的stuno标号 ids Araay数组
public List<Student> findByArray(int[] ids);
2在小配置中配置
<!-- array数组 -->
<select id="findByArray" resultType="Student">
select * from student <!-- where =1如果有where标签就不需要 -->
<if test="array.length>0">
where stuno in <!-- item是自定义的 -->
<foreach collection="array" open="(" close=")" separator="," item="myid">
#{myid}
</foreach>
</if> </select>
3在测试类
//数组
@Test
public void findStudentBychoose() throws IOException{
int[] ids={3,11};//自定义数组
List<Student> findByArray = dao.findByArray(ids);
for (Student student : findByArray) {
System.out.println(student.getStuname());
} }
（二）自定义泛型
1在接口中
//查询3,11 ids List自定义泛型
public List<Student> findByListGeneric(List<Student> list);
2在小配置中配置
<!-- list集合 -->
<select id="findByListGeneric" resultType="Student">
select * from student <!-- where =1如果有where标签就不需要 -->
<if test="list.size>0">
where stuno in
<foreach collection="list" open="(" close=")" separator="," item="stu">
#{stu.stuno}
</foreach>
</if> </select>
3在测试类中
//自定义泛型
@Test
public void findByListGeneric() throws IOException{
List<Student> rlist=new ArrayList<Student>();
Student stu1=new Student();
stu1.setStuno(3); Student stu2=new Student();
stu2.setStuno(11); rlist.add(stu2);
rlist.add(stu1);
List<Student> findByListGeneric = dao.findByListGeneric(rlist);
for (Student student : findByListGeneric) {
System.out.println(student.getStuname());
}
（三）List集合
1在接口
//查询3,11 ids List
public List<Student> findByList(List<Integer> list);
2在小配置中配置
<select id="findByList" resultType="Student">
select * from student <!-- where =1如果有where标签就不需要 -->
<if test="list.size>0">
where stuno in
<foreach collection="list" open="(" close=")" separator="," item="stulist">
#{stulist}
</foreach>
</if> </select>
3在测试类
//list集合
@Test
public void findByList() throws IOException{
List<Integer> rlist=new ArrayList<Integer>();
rlist.add(3);
rlist.add(11);
List<Student> findByList = dao.findByList(rlist);
for (Student student : findByList) {
System.out.println(student.getStuname());
} }
五、sql片段
1连接上一个foreach智能标签在小配置中（用include标签）
<!-- sql片段 -->
<sql id="sqlclum" >
select stuno,stuname,stuage,studate
</sql>
<!-- list集合 -->
<select id="findByList" resultType="Student">
<!-- select * from student --><!-- where =1如果有where标签就不需要 -->
<include refid="sqlclum"/> from student
<if test="list.size>0">
where stuno in
<foreach collection="list" open="(" close=")" separator=","
item="stulist">
#{stulist}
</foreach>
</if> </select>