I guess for most java developer has been used framework [Mybatis] , today's topic is about how we check collection List in our code, there different way we can use, the first one is annotation @Select or xml file to write in our project . Sometimes will have some strange situation which is we use @Select annotation to query data we can't get data if we use [if test='postIdList!=null and postIdList.size()>0'] then if we use [if test='postIdList!=null and postIdList.size>0'] can get data from database query. so please remember once we use @Select annotation to query data we should use way of test='postIdList!=null and postIdList.size>0 .