Rails：创建新记录时更新连接表自定义属性

Question

假设我有两个模型：Performance 和 Band，为了连接这两个模型，我有一个名为 performers 的连接表。我的 ActiveRecord 模型设置如下：

class Band < ApplicationRecord
  has_many :performers
  has_many :performances, through: :performers, dependent: :destroy
end

class Performance < ApplicationRecord
  has_many :performers
  has_many :bands, through: :performers, dependent: :destroy
end

class Performer < ApplicationRecord
  belongs_to :band
  belongs_to :performance
end

现在是棘手的部分。我在performers 表中有一个名为permissions 的自定义属性，它捕获表演者的权限级别（所有者、编辑者、查看者），它定义了谁可以对表演进行更改。这让我想到了我的问题：当一个乐队创建一个新的表演时，我如何在创建过程中在连接表上设置一个值，例如

    def create
      performance = Performance.new(performance_params)
      # here I add a performance to a band's performances, which creates a new performer record
      band.performances << performance
      # what I would also like to do (at the same time if possible) is also define the permission level 
      # during creation something like but:
      performer = band.performers.last
      performer.permissions = 'owner'
      performer.save
      render json: serialize(performance), status: 200 
    end

Rails 中有什么东西可以让我在创建关联时修改连接表属性吗？

编辑

作为参考，我现在这样做：

def create
     performance = Performance.new(performance_params)
     performer = Performer.new
     performer.band = Band.find(params[:band_id])
     performer.permissions = 'owner'
     performance.performers << performer
     performance.save!
     render json: serialize(performance), status: 200
end

但想知道是否有更简单的方法。

Answer 1

您可以在has_many 上使用Association Callbacks 或将适当的callback 添加到Performer 模型，因为即使它正在加入模型，它仍然是作为模型创建的。

类似：

class Performer < ApplicationRecord
  belongs_to :band
  belongs_to :performance

  before_create :set_permissions

  private

  def set_permissions
    self.permissions = 'owner'
  end
end