Rails：创建新记录时更新连接表自定义属性

Question

Lets say I have two models: Performance and Band , and to connect the two I have a join table called performers . My ActiveRecord models are setup as follows:

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

Now the tricky part. I have a custom attribute called permissions in the performers table that captures the permission levels (owner, editor, viewer) for a performer, which defines who can make changes to a performance. Which brings me to my question: when a band creates a new performance, how can I set a value on the join table during creation eg

    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

Is there something in Rails that can let me modify a join tables attribute during creation of an association?

EDIT

For reference, right now I do:

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

But was wondering if there was something simpler.

Answer 1

You can use either Association Callbacks on has_many or add appropriate callback to Performer model as it's still created as a model even it's joining one.

Something like:

class Performer < ApplicationRecord
  belongs_to :band
  belongs_to :performance

  before_create :set_permissions

  private

  def set_permissions
    self.permissions = 'owner'
  end
end