Question

在HQL方面，我相当缺乏经验，所以我想知道是否有人可以帮助我解决这个问题。我有一个关系，学生与StudentCollege有一个OneToMany关系。我试图编写一个查询，查找已经创建了应用程序的每个学生，以及他们提交了多少个应用程序。我写了下面的查询，但我不确定它是否接近我应该做的事情。

select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) " +
                    "from StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 order by stu.last_name

当它运行时，抛出以下异常：

org.hibernate.hql.ast.QuerySyntaxException: Unable to locate appropriate constructor on class [package.location.ReportVO] [select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) from package.location.StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 order by stu.last_name]

但是我有一个VO对象的构造函数，它接受相同数量的参数，所以我认为从 sum 返回的类型是不正确的。我还尝试将 numApplications 替换为整数和计数，但会抛出相同的异常。

public ReportVO(int id, String firstName, String lastName, int year, String school, Integer numApplications)

感谢任何帮助！

Answer 1

我相信你在where子句之后缺少一个“group by”子句。

select distinct new ReportVO (stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name, sum(case when si.applied = 1 then 1 else 0 end) as numApplications) " +
                    "from StudentCollege as si join si.student as stu where stu.year <= 12 and stu.user.id = :userId and si.applied = 1 group by stu.id, stu.first_name, stu.last_name, stu.year, stu.school.school_name order by stu.last_name

HQL：在查询中有条件地计算子集合

1 个答案: