eg:
<if test="id != null"> id=#{id} </if> <if test="id != null and username.trim() != ''"> id=#{id} </if> <if test="id == 0 or username.trim() != ''"> id=#{id} </if> trim标签prefix:前缀,给拼凑的sql语句加一个前缀 prefixOverrides:前缀覆盖,去掉前缀中多余的字符 suffix:给拼凑的sql语句加一个后缀 suffixOverrides:后缀覆盖,去掉后缀中多余的字符
<trim prefix="where" prefixOverrides="and" suffix="" suffixOverrides="and"> <if test="id != null"> id=#{id} </if> <if test="id != null and username.trim() != ''"> and id=#{id} </if> <if test="id == 0 or username.trim() != ''"> id=#{id} </if> </trim> choose标签 <choose> <when test="id != null"> id=#{id} </when> <when test="lastName != null"> lastName=#{lastName} </when> <otherwise> 1=1 </otherwise> </choose> set标签 如果结尾有一个逗号,set标签会帮你清除。 <set> <if test="id != null"> id=#{id}, </if> <if test="id != null and username.trim() != ''"> id=#{id}, </if> <if test="id == 0 or username.trim() != ''"> id=#{id}, </if> </set> where标签 如果前面有and会帮你去掉and,但不能截取sql语句后面带上的and。 <where> <if test="id != null"> id=#{id} </if> <if test="id != null and username.trim() != ''"> and id=#{id} </if> <if test="id == 0 or username.trim() != ''"> and id=#{id} </if> </where> foreach标签原生SQL：
select * from user where id in(1,2,3)改成MyBatis：
<foreach collection="ids" item="id" separator="," open="(" close=")"> #{id} </foreach>当然foreach中还有index属性
当集合为List的时候 index表示的时候集合的索引当集合为map的时候 index表示map的key 而item表示的是map的value foreach插入多个数据 格式：insert ... values <foreach collection="users" item="use" separator="," > ( #{user.name},#{user.password} ...) </foreach>oracle批量插入：
<insert id="..."> <foreach collection="users" item="user" open="begin" close="end"> insert into xxxx values(#{user.xxx},#{user.yyy}...) </foreach> </insert>