Question

Type specified for TypedQuery [com.softtrends.college.model.Student] is incompatible with query return type [class java.lang.String]; nested exception is java.lang.IllegalArgumentException: Type specified for TypedQuery [com.softtrends.college.model.Student] is incompatible with query return type [class java.lang.String]

这是控制器编码

//http://localhost:8080/college/subjectmaps/find?college=GCOEJ&subject=science&professor=R.S.Agrawal
    @RequestMapping(value="/find", method = RequestMethod.GET)
    public String findCollegeForCity(Model uiModel, @RequestParam(value = "college", required = true) String pCollege,
           @RequestParam(value = "subject", required = false) String pSubject,
           @RequestParam(value = "professor", required = false) String pProfessor,
           @RequestParam(value = "page", required = false) Integer page,
           @RequestParam(value = "size", required = false) Integer size) {
        if (page != null || size != null) {
            int sizeNo = size == null ? 10 : size.intValue();
            final int firstResult = page == null ? 0 : (page.intValue() - 1) * sizeNo;
            uiModel.addAttribute("Subjectmaps", Subjectmap.listStudents(pCollege, pSubject, pProfessor, firstResult, sizeNo));
            float nrOfPages = (float) Subjectmap.countStudents(pCollege, pSubject, pProfessor) / sizeNo;
            uiModel.addAttribute("maxPages", (int) ((nrOfPages > (int) nrOfPages || nrOfPages == 0.0) ? nrOfPages + 1 : nrOfPages));
        } else {
            uiModel.addAttribute("Subjectmaps", Subjectmap.listStudents(pCollege, pSubject, pProfessor));
        }
        return "Subjectmaps/list";
    }

the following queries i wrote in model 

//list students studying a subject in a college under a professor.(college is mandatory)
    public static List<Student> listStudents(String pCollege, String pSubject, String pProfessor) {
        return entityManager().createQuery("SELECT o.studentId.studentName from Subjectmap o WHERE o.studentId.collegeId.collegeName=?1 AND (?2 IS null or o.subjectId.subjectName=?2) AND (?3 IS null OR o.professorId.professorName=?3)", Student.class)
                .setParameter(1, pCollege)
                .setParameter(2, pSubject)
                .setParameter(3, pProfessor)
                .getResultList();
    }

    public static long countStudents(String pCollege, String pSubject, String pProfessor) {
        return entityManager().createQuery("SELECT o.studentId.studentName from Subjectmap o WHERE o.studentId.collegeId.collegeName=?1 AND (?2 IS null or o.subjectId.subjectName=?2) AND (?3 IS null OR o.professorId.professorName=?3)", Long.class)
                .setParameter(1, pCollege)
                .setParameter(2, pSubject)
                .setParameter(3, pProfessor)
                .getSingleResult();
    }

    public static List<Student> listStudents(String pCollege, String pSubject, String pProfessor, int pFirstResults, int pMaxResults) {
        return entityManager().createQuery("SELECT o.studentId.studentName from Subjectmap o WHERE o.studentId.collegeId.collegeName=?1 AND (?2 IS null or o.subjectId.subjectName=?2) AND (?3 IS null OR o.professorId.professorName=?3)", Student.class)
                .setParameter(1, pCollege)
                .setParameter(2, pSubject)
                .setParameter(3, pProfessor)
                .setFirstResult(pFirstResults)
                .setMaxResults(pMaxResults)
                .getResultList();
    }

Answer 1

listStudents()中的查询错误：您选择学生的姓名，但期望学生：SELECT o.studentId.studentName ...

也许这会奏效:(删除“.studentName”）

 return entityManager().createQuery("SELECT o.studentId from Subjectmap o WHERE o.studentId.collegeId.collegeName=?1 AND (?2 IS null or o.subjectId.subjectName=?2) AND (?3 IS null OR o.professorId.professorName=?3)", Student.class)

如果没有，你可能不得不加入学生的桌子。

如何解决我得到的以下错误？

1 个答案: