Ecto:如何访问预加载关联的字段

Question

我试图让与friend_referral_code无关的用户，或者他们的代码状态为假，他们也没有使用任何代码。但是我无法访问预加载关联friend_referral_code的字段状态。以下是我的做法：

def get_first_free_invite_users() do
users =
list_users()
|> Repo.preload([:friend_referral_code])
|> Enum.filter(
fn u ->
u.friend_referral_code == [] or u.friend_referral_code["status"] == false and
Repo.all(from ref in FriendReferralCode,
where: ref.receiver_id == ^u.id and ref.status == true) == []
end)
users
end

它会在u.friend_referral_code.status == false上抛出错误。我不能加入的原因是，FriendReferralCode中可能没有特定用户的记录，我想捕获这些用户。以下是加载关联的方式：

friend_referral_code: [
%MyApp.Accounts.FriendReferralCode{
__meta__: #Ecto.Schema.Metadata<:loaded, "friend_referral_code">,
challenge: #Ecto.Association.NotLoaded<association :challenge is not loaded>,
challenge_id: nil,
code: "RFQTS",
expiry: 1,
id: 16021,
inserted_at: ~N[2021-02-01 11:55:00],
order: 1,
prize: #Decimal<3>,
receiver: #Ecto.Association.NotLoaded<association :receiver is not loaded>,
receiver_id: 15002,
state: "create_competition",
status: false,
updated_at: ~N[2021-02-01 11:57:20],
user: #Ecto.Association.NotLoaded<association :user is not loaded>,
user_id: 15001
}
],

Answer 1

它会在 u.friend_referral_code.status == false 上抛出错误。

这是因为u.friend_referral_code是您示例中的列表。您需要枚举u.friend_referral_code并检查每个状态。

尝试这样的事情。

def get_ref_codes_by_user(id) do
Repo.all(from ref in FriendReferralCode,
where: ref.receiver_id == ^u.id and ref.status == true)
end
def filter_referrals([], user_id, acc), do: acc
def filter_referrals([ref, rest], user_id, acc) do
is_used = 
ref == [] || ref.status == false && get_ref_codes_by_user(id) == []

new_acc = 
case is_used do
true -> acc
false -> [ref | acc]
end
filter_referrals(rest, user_id, new_acc)
end
def get_first_free_invite_users() do
list_users()
|> Repo.preload([:friend_referral_code])
|> Enum.map(
fn u ->
filter_referrals(u.friend_referral_code, u.id, [])
end)
end

这将使您更接近并为您提供FriendReferralCode列表。 仔细检查逻辑是否是您想要的。综上所述，您应该能够通过联接来执行此操作。查看此处的文档以及有关联接类型的其他 SO 答案。

尝试

Repo.all(from ref in FriendReferralCode,
right_join users u on ref.user_id =  u.id
where: ref.status == true)