MyBatis进阶（＜if＞＜trim＞＜where＞＜set＞＜foreach＞＜include＞标签的使用）

本文主要是介绍MyBatis进阶（＜if＞＜trim＞＜where＞＜set＞＜foreach＞＜include＞标签的使用），希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

目录

< if >标签

< trim >标签

< where >标签

< set >标签

< foreach >标签

< include >标签

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< if >标签

非必填字段

xml实现

<insert id="insertUserByCondition">INSERT INTO userinfo (username,`password`,age,<if test="gender != null">gender,</if>phone)VALUES (#{username},#{age},<if test="gender != null">#{gender},</if>#{phone})
</insert>

注解实现（不推荐）

@Insert("<script>" +"INSERT INTO userinfo (username,`password`,age," +"<if test='gender!=null'>gender,</if>" +"phone)" +"VALUES(#{username},#{age}," +"<if test='gender!=null'>#{gender},</if>" +"#{phone})"+"</script>")
Integer insertUserByCondition(UserInfo userInfo);

< trim >标签

• prefix：表⽰整个语句块，以prefix的值作为前缀

• suffix：表⽰整个语句块，以suffix的值作为后缀

• prefixOverrides：表⽰整个语句块要去除掉的前缀

• suffixOverrides：表⽰整个语句块要去除掉的后缀

有多个字段是选填项时，考虑采用此方式

xml方式

<insert id="insertUserByCondition">INSERT INTO userinfo<trim prefix="(" suffix=")" suffixOverrides=","><if test="username !=null">username,</if><if test="password !=null">`password`,</if><if test="age != null">age,</if><if test="gender != null">gender,</if><if test="phone != null">phone,</if></trim>VALUES<trim prefix="(" suffix=")" suffixOverrides=","><if test="username !=null">#{username},</if><if test="password !=null">#{password},</if><if test="age != null">#{age},</if><if test="gender != null">#{gender},</if><if test="phone != null">#{phone}</if></trim>
</insert>

注解方式（不推荐）

@Insert("<script>" +"INSERT INTO userinfo " +"<trim prefix='(' suffix=')' suffixOverrides=','>" +"<if test='username!=null'>username,</if>" +"<if test='password!=null'>password,</if>" +"<if test='age!=null'>age,</if>" +"<if test='gender!=null'>gender,</if>" +"<if test='phone!=null'>phone,</if>" +"</trim>" +"VALUES " +"<trim prefix='(' suffix=')' suffixOverrides=','>" +"<if test='username!=null'>#{username},</if>" +"<if test='password!=null'>#{password},</if>" +"<if test='age!=null'>#{age},</if>" +"<if test='gender!=null'>#{gender},</if>" +"<if test='phone!=null'>#{phone}</if>" +"</trim>"+"</script>")
Integer insertUserByCondition(UserInfo userInfo);

< where >标签

xml实现

<select id="queryByCondition" resultType="com.example.demo.model.UserInfo">select id, username, age, gender, phone, delete_flag, create_time, 
update_timefrom userinfo<where><if test="age != null">and age = #{age}</if><if test="gender != null">and gender = #{gender}</if>
<if test="deleteFlag != null">and delete_flag = #{deleteFlag}</if></where>
</select>

注解方式

@Select("<script>select id, username, age, gender, phone, delete_flag, 
create_time, update_time" +" from userinfo" +" <where>" +" <if test='age != null'> and age = #{age} </if>" +" <if test='gender != null'> and gender = #{gender} </if>" +" <if test='deleteFlag != null'> and delete_flag = #
{deleteFlag} </if>" +" </where>" +"</script>")
List<UserInfo> queryByCondition(UserInfo userInfo);

<where>只会在⼦元素有内容的情况下才插⼊where⼦句，⽽且会⾃动去除⼦句的开头的AND或 OR

以上标签也可以使⽤<trim prefix="where" prefixOverrides="and">替换,但是此种情况下,当⼦元素都没有内容时,where关键字也会保留

< set >标签

动态的在SQL语句中插⼊set关键字，并会删掉额外的逗号.(⽤于update语句中)

也可以使⽤<trim prefix="set" suffixOverrides=",">替换

xml方式

<update id="updateUserByCondition">update userinfo<set><if test="username != null">username = #{username},</if><if test="age != null">age = #{age},</if><if test="deleteFlag != null">delete_flag = #{deleteFlag},</if></set>where id = #{id}
</update>

注解方式

@Update("<script>" +"update userinfo " +"<set>" +"<if test='username!=null'>username=#{username},</if>" +"<if test='age!=null'>age=#{age},</if>" +"<if test='deleteFlag!=null'>delete_flag=#{deleteFlag},</if>" +"</set>" +"where id=#{id}" +"</script>")
Integer updateUserByCondition(UserInfo userInfo);

< foreach >标签

对集合进行遍历

• collection：绑定⽅法参数中的集合，如List，Set，Map或数组对象

• item：遍历时的每⼀个对象

• open：语句块开头的字符串

• close：语句块结束的字符串

• separator：每次遍历之间间隔的字符串

void deleteByIds(List<Integer> ids);

xml方式 

<delete id="deleteByIds">delete from userinfowhere id in<foreach collection="ids" item="id" separator="," open="(" close=")">#{id}</foreach>
</delete>

注解方式 

@Delete("<script>" +"delete from userinfo where id in" +"<foreach collection='ids' item='id' separator=',' open='(' 
close=')'>" +"#{id}" +"</foreach>" +"</script>")
Integer deleteUser(Integer id);

< include >标签

对重复代码片段使用<sql>封装，再通过<include>标签进行引用

<sql id="allColumn">id, username, age, gender, phone, delete_flag, create_time, update_time
</sql>

<select id="queryAllUser" resultMap="BaseMap">select<include refid="allColumn"></include>from userinfo
</select>
<select id="queryById" resultType="com.example.demo.model.UserInfo">select<include refid="allColumn"></include>from userinfo where id= #{id}
</select>

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