Question

我试图创建一种构建＆＃34;嵌套＆＃34;的方法。路径对象。我想要的是这样的

public Path<?> getPath(Path<?>path, SingularAttribute<?, ?>attribute) {
    return path.get(attribute);
}

但是我收到以下错误：

error: no suitable method found for get(SingularAttribute<CAP#1,CAP#2>)
        return path.get(attribute);
    method Path.<Y#1>get(SingularAttribute<? super CAP#3,Y#1>) is not applicable
      (cannot infer type-variable(s) Y#1
        (argument mismatch; SingularAttribute<CAP#1,CAP#2> cannot be converted to SingularAttribute<? super CAP#3,Y#1>))
    method Path.<E,C>get(PluralAttribute<CAP#3,C,E>) is not applicable
      (cannot infer type-variable(s) E,C
        (argument mismatch; SingularAttribute<CAP#1,CAP#2> cannot be converted to PluralAttribute<CAP#3,C,E>))
    method Path.<K,V,M>get(MapAttribute<CAP#3,K,V>) is not applicable
      (cannot infer type-variable(s) K,V,M
        (argument mismatch; SingularAttribute<CAP#1,CAP#2> cannot be converted to MapAttribute<CAP#3,K,V>))
    method Path.<Y#2>get(String) is not applicable
      (cannot infer type-variable(s) Y#2
        (argument mismatch; SingularAttribute<CAP#1,CAP#2> cannot be converted to String))
  where Y#1,X,E,C,K,V,M,Y#2 are type-variables:
    Y#1 extends Object declared in method <Y#1>get(SingularAttribute<? super X,Y#1>)
    X extends Object declared in interface Path
    E extends Object declared in method <E,C>get(PluralAttribute<X,C,E>)
    C extends Collection<E> declared in method <E,C>get(PluralAttribute<X,C,E>)
    K extends Object declared in method <K,V,M>get(MapAttribute<X,K,V>)
    V extends Object declared in method <K,V,M>get(MapAttribute<X,K,V>)
    M extends Map<K,V> declared in method <K,V,M>get(MapAttribute<X,K,V>)
    Y#2 extends Object declared in method <Y#2>get(String)
  where CAP#1,CAP#2,CAP#3 are fresh type-variables:
    CAP#1 extends Object from capture of ?
    CAP#2 extends Object from capture of ?
    CAP#3 extends Object from capture of ?

有关如何解决此错误的任何建议吗？非常感谢。

更新我找到了使用辅助方法的快速解决方法：

public Path<?> getPath(Path<?> path, SingularAttribute<?, ?> attribute) {
    return getPathHelper(path, attribute);
}

@SuppressWarnings("unchecked")
private <X, Y> Path<Y> getPathHelper(Path<X>, SingularAttribute<?, ?> attribute) {
    return path.get((SingularAttribute<? super X, Y>) attribute);
}

这可以，但这段代码是正确的吗？

Answer 1

您可以使用

public <X, Y> Path<Y> getPath(Path<X> path, SingularAttribute<? super X, Y> attribute) {
    return path.get(attribute);
}

此方法签名比以前更具限制性，因此您必须检查它是否适用于您的情况。

编写它是为了匹配Path.get方法的返回类型。

希望这有帮助。

JPA Criteria路径导航

1 个答案: