JPQL:SELECT NEW查询中的枚举文字

Question

我有几个域类的描述符类.描述符类有一个字段'type',它是一个枚举,表示域类的类型.在某些查询中,我想返回或更多描述符,并将类型作为构造函数参数传递.所以我的想法是将它作为查询参数传递:

  String jpql = "SELECT NEW model.ModelDescriptor"
    + "(t.id, t.name, t.description, :modelType) ... ";
  TypedQuery<ModelDescriptor> query = em.createQuery(jpql, ModelDescriptor.class);
  query.setParameter("modelType", ModelType.forClass(clazz));
  List<ModelDescriptor> list = query.getResultList();

这不起作用.没有抛出异常,但类型null在结果中.此外,无法将枚举文字传递给查询:

  "SELECT NEW model.ModelDescriptor (f.id, f.name, f.description,   
    model.ModelType.FLOW) ... "

编辑 我得到以下堆栈跟踪:

  java.lang.IllegalArgumentException: An exception occurred while creating a query in 
  EntityManager: 
  Exception Description: Error compiling the query [SELECT model.ModelDescriptor(f.id,
  f.name, f.description, model.ModelType.FLOW) FROM Flow f WHERE flow.id = :flowId], 
  line 1, column 78: unknown identification variable [model]. The FROM clause of the
  query does not declare an identification variable [model].
  at org.eclipse.persistence.internal.jpa.EntityManagerImpl.
         createQuery(EntityManagerImpl.java:1477)
  at org.eclipse.persistence.internal.jpa.EntityManagerImpl.
          createQuery(EntityManagerImpl.java:1497)

我使用EclipseLink作为持久性框架.

有没有办法将枚举文字传递给SELECT NEW表达式？

Answer 1

没有,通常没有办法引用任何类中的字段,也不可能将参数传递给SELECT子句.只有构造函数表达式的有效参数是(来自JPA 2.0规范,第174页)

• single_valued_pa​​th_expression
• scalar_expression
• aggregate_expression
• identification_variable