ndb 多对多，检索关系之一的列表

Question

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 Table Club 我有这个

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？

获取此查询，然后使用 for 循环获取每个 member 使用其键？

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

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

Answer 1

get_multi 适用于键列表，您有一个 ClubMembership 实例列表。您需要为每个人获取 member 密钥：

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

Answer 2

您还应考虑将会员信息存储在用户实体内。这样你就可以在一个查询中获取所有用户，速度要快得多。

class Membership(ndb.Model):
  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)

class User(ndb.Model):
  memberships = ndb.StructuredProperty(Membership, repeated=True)

class Club(ndb.Model):
  @property
  def members(self):
    membership = Membership(
      User.memberships.club == self.key,
      User.memberships.membership_type == 'MEMBER',
      User.memberships.is_active == True)
    return User.query(User.memberships == membership)

ndb 多对多，检索关系之一的列表

ndb many to many, retrieve list of one of the relation

python

google-app-engine

google-cloud-datastore

data-modeling

app-engine-ndb