Question

我有三个表：

class Keeper
  has_many :assignments
end

class Assignment
  belongs_to :keeper
  belongs_to :assignment_group
end

class AssignmentsGroup
  has_many :assignments
  validate :uniqueness_of_keeper
end

与一个assignment_group相关联的分配必须具有一个守护者。我的问题是：鉴于所有关联的工作分配都具有相同的管理者，我如何向has_one: keeper添加AssignmentsGroup关联？

Answer 1

很抱歉，如果我误解了您的问题，因为目前尚不清楚AssignmentGroup和Assignment之间应该建立什么关联，请尝试以下方法：

class Keeper
  has_many :assignments
end

class Assignment
  belongs_to :keeper
  belongs_to :assignment_group # will need to add a reference to the assignments table
end

class AssignmentsGroup
  has_many :assignments
  has_many :keepers, through: assignments
  validate :single_keeper

  private     

  def single_keeper
    errors.add(:base, "can only have one keeper") unless keepers.uniq.length == 1
  end
end

请参见https://guides.rubyonrails.org/active_record_validations.html#custom-methods

具有动态条件的has_one关联的has_one关联-Rails

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