Mybatis的动态SQL(if、where、choose、bind、set、foreach标签)
1．if
单分支判断语句
<select id="selectUserByProperty" resultType="com.zd.pojo.Users">
select * from users where 1=1
<if test="userid!=0">
and userid=#{userid}
</if>
<if test="username!=null and username!=''">
and username=#{username}
</if>
<if test="usersex!=null and usersex!=''">
and usersex=#{usersex}
</if>
</select>
@Test
public void selectUserByProperty(){
SqlSession sqlSession = MybatisUtil.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Users users=new Users(0,"张三","男");
Users users1 = userDao.selectUserByProperty(users);
System.out.println(users1);
}
2 ．choose、when、otherwise
从多个条件中选择一个
<!--动态SQL choose-->
<select id="selectUserChoose" parameterType="com.zd.pojo.Users" resultType="com.zd.pojo.Users">
select * from users where 1=1
<choose>
<when test="username!=null and username!=''">
and username=#{username}
</when>
<when test="usersex!=null and usersex!=''">
and usersex=#{usersex}
</when>
<otherwise>
and userid=1
</otherwise>
</choose>
</select>
当第一个when满足时就不再拼接后面的条件，都不满足是执行otherwise的条件
@Test
public void selectUserChoose(){
SqlSession sqlSession = MybatisUtil.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Users users=new Users(0,"张三","男");
Users users1 = userDao.selectUserChoose(users);
System.out.println(users1);
}
3．where标签
使用where标签，就不需要提供where 1=1 这样的条件了。如果判断判断条件不为空，自动添加where关键字，并且会自动去掉第一个条件前面的and和or
<!--动态SQL where-->
<select id="selectWhere" resultType="com.zd.pojo.Users">
select * from users
<where>
<choose>
<when test="username!=null and username!=''">
username=#{username}
</when>
<when test="usersex!=null and usersex!=''">
usersex=#{usersex}
</when>
<otherwise>
userid=1
</otherwise>
</choose>
</where>
</select>
4 ．bind标签
bind标签允许我们在OGNL表达式以外创建一个变量，并可以将其绑定到当前的SQL语句中。一般应用于模糊查询，通过bind绑定通配符和查询值
<!--模糊查询-->
<select id="selectUserByName" parameterType="com.zd.pojo.Users">
<bind name="likeName" value="'%'+_parameter+'%'"/>
select * from users where username like #{likeName}
</select>
参数类型为String时value必须写_parameter或者注解@Param绑定参数
5．set标签
set标签用在update语句中。借助if标签，可以只对有具体值得字段进行更新。set标签会自动添加set关键字，自动去掉最后一个if语句的多余的逗号
<!--选择更新-->
<update id="updateUser" parameterType="com.zd.pojo.Users">
update users
<set>
<if test="username!=null and username!=''">
username=#{username},
</if>
<if test="usersex!=null and usersex!=''">
usersex=#{usersex},
</if>
</set>
where userid=#{userid}
</update>
@Test
public void updateUser(){
SqlSession sqlSession = MybatisUtil.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Users user=new Users(1,"Jack","man");
userDao.updateUser(user);
System.out.println(userDao.selectUsersById(1));
}
６．foreach标签
foreach可以迭代List、Set、Map或者数组对象
迭代集合
类型： collection=“collection”
名称：List selectUserByIdCollection(@Param(“suibian”)List list);
collection=“suibian”
<!--查询用户id为1，2，3的用户-->
<!--select * from users where userid in (1,2,3)-->
<select id="selectUserByIdCollection" resultType="com.zd.pojo.Users">
select * from users where userid in
<foreach collection="collection" item="userid" open="(" separator="," close=")">
#{userid}
</foreach>
</select>
List<Users> selectUserByIdCollection(List<Integer> list);
迭代数组
类型： collection=“array”
名称 List selectUserByIdArray(@param(“suibian”)Integer[] arr);
<!--查询用户id为1，2，3的用户-->
<!--select * from users where userid in (1,2,3) 数组-->
<select id="selectUserByIdArray" resultType="com.zd.pojo.Users">
select * from users where userid in
<foreach collection="array" item="userid" open="(" separator="," close=")">
#{userid}
</foreach>
</select>
迭代map
只能通过名称的方式绑定collection
//动态SQL foreach迭代Map
int selectUserCountMap(@Param("map") Map<String,String> map);
<!--根据给定的条件做计数 select count(*) from users where username=? and usersex=?-->
<select id="selectUserCountMap" resultType="int">
select count(*) from users where
<foreach collection="map" separator="and" item="value" index="key">
${key}=#{value}
</foreach>
</select>
@Test
public void selectUserCountMap(){
SqlSession sqlSession=MybatisUtil.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Map<String,String> map=new HashMap<>();
map.put("usersex","男");
int i = userDao.selectUserCountMap(map);
System.out.println("i = " + i);
}
批量添加数据
//批量添加
int insertUserForeach(List<Users> list);
<!--动态批量添加 insert into users values (default,?,?),(default,?,?)-->
<insert id="insertUserForeach">
insert into users values
<foreach collection="collection" item="users" separator=",">
(default,#{
users.username},#{
users.usersex})
</foreach>
</insert>
@Test
public void insertUserForeach(){
SqlSession sqlSession=MybatisUtil.getSqlSession();
UserDao userDao = sqlSession.getMapper(UserDao.class);
Users users1=new Users("李白","男");
Users users2=new Users("杨玉环","女");
Users users3=new Users("武则天","女");
List<Users> list=new ArrayList<>();
list.add(users1);
list.add(users2);
list.add(users3);
int i = userDao.insertUserForeach(list);
System.out.println("共添加"+i+"条数据");
sqlSession.commit();
}
