java - 从 boolean 函数中选择

我正在尝试使用Java EE开发应用程序。这是我要实现的类图的一部分：



这是hibernate类的实现：

@Entity
@Table(name = "t_enseignant")
public class Enseignant extends User implements Serializable {


private static final long serialVersionUID = 1L;

    private String specialite;
    private List<Module> modules;

    public Enseignant() {
    }

    public Enseignant(String nom, String prenom, String email, String login, String password, String specialite) {
        super(nom, prenom, email, login, password);
        this.setSpecialite(specialite);
    }

    public String getSpecialite() {
        return specialite;
    }

    public void setSpecialite(String specialite) {
        this.specialite = specialite;
    }

    @OneToMany(mappedBy = "enseignant")
    public List<Module> getModules() {
        return modules;
    }

    public void setModules(List<Module> modules) {
        this.modules = modules;
    }
}

@Entity
@Table(name = "t_classe")
public class Classe implements Serializable {

    private static final long serialVersionUID = 1L;

    private int id;
    private String niveau;
    private int nbreEtudiant;

    private List<Module> modules;

    public Classe() {
    }

    public Classe(String niveau, int nbreEtudiant) {
        this.niveau = niveau;
        this.nbreEtudiant = nbreEtudiant;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int getId() {
        return id;
    }

...

我还实现了Module Class和ModulePK。
我想检查一下是否应该一次指派一位老师上课。
我尝试了以下JPQL查询

boolean exists = false;
    String jpql = "select case when (count(m) > 0)  then true else false end  from Module m where m.idEnseignant=idEnseignant and m.idClasse=idClasse";
    TypedQuery<Boolean> query = entityManager.createQuery(jpql, Boolean.class);
    query.setParameter("idEnseignant", enseignant.getId());
    query.setParameter("idClasse", classeToValidate.getId());
        exists = query.getSingleResult();

但是当我执行该方法时，我有这个异常

could not resolve property: idEnseignant of: domain.Module [select case when     (count(m) > 0)  then true else false end  from domain.Module m where m.idEnseignant=idEnseignant and m.idClasse=idClasse]

最佳答案

您忘记了:来指示您的命名参数，因此您使用的是idEnseignant=idEnseignant而不是idEnseignant=:idEnseignant

这是更正的代码：

boolean exists = false;
String jpql = "select case when (count(m) > 0)  then true else false end  from Module m where m.idEnseignant=:idEnseignant and m.idClasse=:idClasse";
TypedQuery<Boolean> query = entityManager.createQuery(jpql, Boolean.class);
query.setParameter("idEnseignant", enseignant.getId());
query.setParameter("idClasse", classeToValidate.getId());
exists = query.getSingleResult();
return exists