Ya投影就像过滤和选择用户名你应该改变它为

Ya projection is like filtering and selecting by username you should change it to

def criteria = User.createCriteria()
def users = criteria.listDistinct() {
    projections {
        groupbyproperty("username")
    }
   // setResultTransformer(CriteriaSpecification.ROOT_ENTITY)
}
return users

工作完成！