ndb 多对多，检索关系之一的列表 [英] ndb many to many, retrieve list of one of the relation

问题描述

我有这张桌子

class ClubMembership(GCModel):
    member = ndb.KeyProperty(kind='User', required=True)
    club = ndb.KeyProperty(kind='Club', required=True)
    is_active = ndb.BooleanProperty(default=True)
    membership_type = ndb.StringProperty(choices=set(["MEMBER", "TRAINER", "OWNER"]), default="MEMBER",
                                     required=True)

然后在表中 Club 我有这个

Then in the Table Club i've this

class Club(GCModel):
    @property
    def members(self):
        return ClubMembership.query(ndb.AND(ClubMembership.club == self.key,
                                            ClubMembership.membership_type == "MEMBER",
                                            ClubMembership.is_active == True))

我真正需要的是检索User 的列表.我该怎么办?

what i actually need is to retrive the list of User. how should i do?

获取此查询，而不是使用 for 循环使用其键获取每个 member ?

fetch this query, than have a for loop that fetches each member using its key?

我尝试使用 ndb.get_multi 使用 member 上的投影，但它不起作用.像这样

i tried to use ndb.get_multi using the projection on member but it does not work. something like this

members= ClubMembership.query(ndb.AND(ClubMembership.club == self.key,
                                            ClubMembership.membership_type == "MEMBER",
                                            ClubMembership.is_active == True),projection=['member']).fetch()
ndb.get_multi(members)

推荐答案

get_multi 处理键列表，您有一个 ClubMembership 实例列表.您需要为每个人获取 member 键:

get_multi works on a list of keys, you have a list of ClubMembership instances. You need to get the member key for each one:

memberships = ClubMembership.query(...)
member_keys = [m.member for m in memberships]
members = ndb.get_multi(member_keys)

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