我正在使用带有Objectify 4.0b3的Google App Engine(Java),并希望在子类SportFacility和UserDefinedFacility中拥有一个超类设施。我希望能够按 id 查询设施,从而从所有子类中获取设施,我还希望能够对每个子类执行相同的操作。
@Entity
public class Facility {
@Id
protected Long id;
@Index
protected String name;
@Index
protected double x_coordinate;
@Index
protected double y_coordinate;
@Index
protected String address;
protected Facility(){}
public Facility(String name, double x_coordinate, double y_coordinate, String address) {
this.name = name;
this.x_coordinate = x_coordinate;
this.y_coordinate = y_coordinate;
this.address = address;
}
@EntitySubclass(index=true)
public class SportFacility extends Facility{
@Index
private String url;
private void SportFacility(){}
public SportFacility(String name, double x_coordinate, double y_coordinate, String address, String url) {
super(name, x_coordinate, y_coordinate, address);
this.url = url;
}
}
@EntitySubclass(index=true)
public class UserDefinedFacility extends Facility{
@Index
private String url;
private void UserDefinedFacility(){}
public UserDefinedFacility(String name, double x_coordinate, double y_coordinate, String address) {
super(name, x_coordinate, y_coordinate, address);
}
}
基本上我的问题与 Objectify 4.0 中的实体层次结构中所述相同,但就我而言,查询
Facility facility = ofy().load().type(Facility.class).id(id);
不起作用,因为AndroidStudio抱怨类型应该是
LoadResult<Facility>
而不是设施。
由于继承概念的语法似乎在 Objectify 版本之间经常更改,因此我找不到有效的解决方案,因此我非常感谢任何帮助!
提前致谢
塞缪尔
Android Studio 是正确的;要获取实体本身,您需要:
Facility facility = ofy().load().type(Facility.class).id(id).now();
或
Facility facility = ofy().load().type(Facility.class).id(id).safe();
如果实体不存在,后者将抛出NotFoundException
(现在将返回null
我记得)。