Rails：查找关系具有指定属性的所有用户

Question

我有三个模型：

class User < ActiveRecord::Base
  has_many :rosterplayers
  has_many :rosters, -> { uniq } ,  :through => :rosterplayers
end

class Roster < ActiveRecord::Base
  has_many :rosterplayers
  has_many :users, -> { uniq }, through: :rosterplayers
end

class Rosterplayer < ActiveRecord::Base
  belongs_to :roster
  belongs_to :user
  validates :user_id, :uniqueness => { :scope => :roster_id }
end

Rosterplayer 表包含三列：user_id、roster_id, 和 pending（布尔值）

问题：给定一个名册，我将如何检索当前待处理的所有用户？

尝试：我的第一次尝试是遍历名册中的所有用户：

@team.rosters[0].users.each do |u|
  Rosterplayer.find_by(roster_id: rosters[0].id, user_id: u.id, pending: true)
end

但我觉得有更好的方法。

Answer 1

您可以通过执行以下操作来实现：

User.includes(:rosterplayers).where(rosterplayers: { pending: true })

这将返回至少有 1 个 rosterplayer 且 pending 设置为 true 的所有用户记录。

将查询限制为特定的roster 实例：

User.includes(:rosterplayers).where(rosterplayers: { pending: true, roster_id: your_roster_id })
# your_roster_id can actually be an array of IDs

---

补充说明：小心使用 .joins 和 .includes：

# consider these models
Post 
  belongs_to :user
                #^^
User
  has_many :posts
               #^

# the `includes/joins` methods use the name defined in the model :
User.includes(:posts).where(posts: { title: 'Bobby Table' })
                  #^            ^
# but the `where` uses the pluralized version (table's name) : 
Post.includes(:user).where(users: { name: 'Bobby' })
                #^^^           ^

---

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