HQL：在查询中有条件地计数子集合

Question

I'm fairly inexperienced when it comes to HQL, so I was wondering if anyone can help me out on this. I have a relationship where Student has a OneToMany relationship with StudentCollege. I'm trying to write a query that finds each student who has made an application, and how many applications they've submitted. I have the following query written, but I am unsure if it's even close to what I should be doing.

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

When it runs the following exception is thrown:

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]

However I have a constructor for the VO object that takes in that same number of arguments, so I'm thinking the type returned from the sum is incorrect. I've also tried replacing numApplications with Integer and Count , but the same exception is thrown.

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

Any help is appreciated!

Answer 1

I believe you are a missing a "group by" clause after the where clause.

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