mybatis动态SQL

if(如果test中的条件满足，则在sql中拼装if之中的条件)

trim自定义sql拼装规则。包括

加前缀 prefix，

加后缀suffix，
去掉前缀prefixOverrides，

去掉后缀suffixOverrides

<select id="getBloggerByDynamicSQL" resultType="com.yunqing.mybatis.bean.Blogger">
SELECT * FROM t_blogger
<!--自定义sql，相当于字符串前缀(没有的话)加一个where,后缀（有的话）去掉一个and-->
<trim prefix="where" suffixOverrides="and">
<if test="id!=null">
WHERE id=#{id} AND
</if>
<if test="username!=null and username!=''">
username=#{username} AND
</if>
<if test="password!=null and password!=''">
password=#{password}
</if>
</trim>
</select>

choose相当于switch case

when满足条件，补上sql跳出

都不满足则补上otherwise中的sql

<select id="getBloggerByChoose" resultType="com.yunqing.mybatis.bean.Blogger">
SELECT * FROM t_blogger
<where>
<choose>
<when test="id!=null">
id=#{id}
</when>
<when test="username!=null and username!=''">
username=#{username}
</when>
<when test="password!=null and password!=''">
password=#{password}
</when>
<otherwise>
profile LIKE #{profile}
</otherwise>
</choose>
</where>
</select>

set相当于修改信息的set,也可以使用trim自定义

<update id="updateBlogger">
UPDATE t_blogger
<set>
<if test="username!=null and username!=''">
username=#{username},
</if>
<if test="password!=null and password!=''">
password=#{password}
</if>
</set>
<where>
id=#{id}
</where>
</update>

自定义写法：

<update id="updateBlogger">
UPDATE t_blogger
<!--相当于给sql字符串前边加上set,后边如果多出，则去掉，-->
<trim prefix="set" suffixOverrides=",">
<if test="username!=null and username!=''">
username=#{username},
</if>
<if test="password!=null and password!=''">
password=#{password}
</if>
</trim>
<where>
id=#{id}
</where>
</update>

foreach:遍历，多用于批量查询，或者批量添加等批量操作

package com.yunqing.mybatis.dao;

import com.yunqing.mybatis.bean.User;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface UserDynamicSQLMapper {

List<User> getUserByDynamicSQL(User user);

void updateUser(User user);

void addUsers(@Param("users") List<User> users);//批量添加

List<User> getAllByIds(@Param("ids") List<Integer> ids);//根据多id查询
}

<!--批量添加
collection:集合名
item:集合中子元素命名
separator:以xx分割<foreach>中的sql
open:<foreach>中的sql以open中的内容开始
close:<foreach>中的sql以open中的内容结束
-->
<insert id="addUsers">
INSERT INTO t_user(name,age,dep_id) VALUES
<foreach collection="users" item="user" separator=",">
(#{user.name},#{user.age},#{user.dep.id})
</foreach>
</insert>

<select id="getAllByIds" resultType="com.yunqing.mybatis.bean.User">
SELECT * FROM t_user WHERE id IN
<foreach collection="ids" item="items" separator="," open="(" close=")">
#{items}
</foreach>
</select>

测试

@Test
public void addUsers() throws IOException {
SqlSession sqlSession = getSqlSessionFactory().openSession(true);
UserDynamicSQLMapper mapper = sqlSession.getMapper(UserDynamicSQLMapper.class);
List<User> list = new ArrayList<>();
list.add(new User(null,"drj",20,new Department(2)));
list.add(new User(null,"LYF",2,new Department(2)));
mapper.addUsers(list);
}
@Test
public void getUserByDynamicSQL() throws IOException {
SqlSession sqlSession = getSqlSessionFactory().openSession();
UserDynamicSQLMapper mapper = sqlSession.getMapper(UserDynamicSQLMapper.class);
/*User user = new User(7,"uzi",20,null);
List<User> userByDynamicSQL = mapper.getUserByDynamicSQL(user);
for (User u : userByDynamicSQL) {
System.out.println(u);
}*/
List<User> allByIds = mapper.getAllByIds(Arrays.asList(1, 2, 3, 19));
for (User u : allByIds) {
System.out.println(u);
}
}

动态sql内置参数有两个：_parameter和_databaseId

<bind>绑定的运用：

<select id="getBloggerByParameter" resultType="com.yunqing.mybatis.bean.Blogger">
SELECT * FROM t_blogger
<!--给传入的参数绑定模糊查询的%，以便在测试的时候可以直接写要模糊查询的内容不用补%-->
<bind name="_profile" value="'%'+profile+'%'"/>
<where>
<if test="_parameter!=null"><!--传入的内置参数-->
profile LIKE #{_profile}
</if>
</where>
</select>

测试：

@Test
public void getBloggerByParam() throws IOException {
SqlSession sqlSession = getSqlSessionFactory().openSession();
BloggerDynamicSQLMapper mapper = sqlSession.getMapper(BloggerDynamicSQLMapper.class);
Blogger blogger = new Blogger();
blogger.setProfile("e");//如果不绑定%%则在此处需要写（“%e%”）
List<Blogger> bloggerByParameter = mapper.getBloggerByParameter(blogger);
for (Blogger blo :
bloggerByParameter) {
System.out.println(blo);
}
}

<sql>标签抽取可重用sql片段，在需要引用可重用片段处使用<include>标签引用。