我正在将Google App Engine(Java)与Objectify 4.0b3配合使用,并希望拥有带有子类SportFacility和UserDefinedFacility的超类设施。我希望能够通过id查询设施,从而从所有子类中获取设施,并且我也希望能够对每个子类都做同样的事情。
@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Entity hierarchies in Objectify 4.0中描述的相同,但在我的情况下,查询
Facility facility = ofy().load().type(Facility.class).id(id);
无法工作,因为AndroidStudio抱怨该类型应为
LoadResult<Facility>
而不是设施。
由于继承概念的语法似乎在Objectify版本之间经常变化,因此我找不到有效的解决方案,因此,我非常感谢您的帮助!
提前致谢
塞缪尔
最佳答案
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();
要么Facility facility = ofy().load().type(Facility.class).id(id).safe();
如果该实体不存在,则后者将抛出一个NotFoundException
(我记得现在将返回null
)。
关于java - EntitySubclass对象化查询,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/26899472/