google-app-engine - 谷歌应用引擎 : reference property that references to 4 models or more

Question

你好我需要向可以引用 4 个不同模型的模型添加一个属性:

class WorldObject(db.Model):
    # type can only accept: text, image, profile, position
    # this should be like a set property in relational database and not a string
    type = db.StringProperty(required = True)

    # ???: this can be a reference to Profile, Image, Position or Text model
    # how to do it?
    reference = db.ReferenceProperty(reference_class = ???, required = True)

谢谢

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@尼克约翰逊:

以下是我在您的帮助下完成的工作:

class WorldObject(db.Model):
# x, y: position in the world
x = db.IntegerProperty(required = True)
y = db.IntegerProperty(required = True)

# world: reference to the world containing it
world = db.ReferenceProperty(reference_class = World)

# profile: is the owner of the object and is the only one who can make changes to it's world object property
owner = db.ReferenceProperty(reference_class = Profile, required = False)

# history
updated = db.DateTimeProperty(auto_now_add = True)
created = db.DateTimeProperty(required = True)

然后:

class ImageWO(WorldObject):
image = db.ReferenceProperty(reference_class = Image, required = False)

然后:

class PositionWO(WorldObject):
position = db.ReferenceProperty(reference_class = Position, required = False)

和其他类是一样的..现在，如果我想获得一个区域中的所有世界对象，我该怎么做？我必须为扩展 world_object 的每个类执行 1 个请求？

Answer 1

Make Profile、Image、Position 和 Text 都扩展了同一个基类，它本身扩展了 Model .然后，将该基类指定为 ReferenceProperty 的目标。无需在 StringProperty 中存储单独的“类型”——这将反射(reflect)在为引用属性存储的键中。