has_one通过与条件关联 [英] has_one through association with condition

问题描述

我有3个相关的表格/模型。我想检索组织聚会的用户，给定Party记录，带有布尔值 organized 的联接表，以及一个用户

I have 3 relevant tables/models. I would like to retrieve the user which has organized a party, given a Party record, a join table with a boolean organized column, and a users table.

到目前为止，我最大的尝试（这对我来说很有意义）。我省略了不相关的列。

My best attempt so far (this one makes the most sense to me after much fiddling). I've omitted the irrelevant columns.

class Party
  # party_id

  has_many   :parties_users
  has_many   :users, through: :parties_users, source: :user
  has_one    :organizer,
             -> { where organizer: true },
             through: :parties_users,
             source: :user

---

---

class PartiesUser
  # party_id
  # user_id
  # organized:bool

  belongs_to :party
  belongs_to :user

---

---

class User
  # user_id
  has_many : parties_users

---

上述设置引发了以下错误，老实说我不完全理解：
ActiveRecord :: HasOneThroughCantAssociateThroughCollection（Cannot有一个has_one：through关联 Party＃organizer，其中：through关联 Party＃parties_users是一个集合。在：through选项中指定has_one或belongs_to关联。）

我知道我可以通过实例方法来执行此操作，但是考虑到使用的频率类型，将其作为关联可以大大受益于我的应用。

I know I can do this via an instance method, but given the frequency types of use, my app would massively benefit from having this as an association.

推荐答案

如错误消息所述，您无法通过has_many获得has_one。

As the error message says, you can't have a has_one through a has_many.

如果组织者标志在连接记录上，您可以（相反）这样做...

You could (instead) do it this way if the organizer flag is on the join record...

has_many :parties_users
has_many :users, through: :parties_users, source: :user
has_one :main_party_user, -> {where organizer: true}, class_name: 'PartiesUser'
has_one :organizer, through: :main_party_user, class_name: 'User'

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