How to pass data to join table on creation

问题

I have the following structure:

class User < ActiveRecord::Base
  has_many :device_ownerships
  has_many :devices, :through => :device_ownerships
end

class Device < ActiveRecord::Base
  has_one :device_ownership
  has_one :user, :through => :device_ownership
end


class DeviceOwnership < ActiveRecord::Base
  belongs_to :user  
  belongs_to :device
end

However DeviceOwnership also has serial_number row

I want to pass serial_number value to DeviceOwnership on create. I understand I can do something like

def create
  user = User.create
  device = Device.create
  device_ownership = DeviceOwnership.create(:serial_numer => params[:device_serial_number], :device_id => device.id, :user_id => user.id)
end

This does not seem too elegant, I wonder if there is a better solution.

回答1:

Use nested attributes:

class User < ActiveRecord::Base

  has_many :device_ownerships
  has_many :devices, :through => :device_ownerships
  accepts_nested_attributes_for :devices
end

class Device < ActiveRecord::Base
  has_one :device_ownership
  has_one :user, :through => :device_ownership
  accepts_nested_attributes_for :device_ownership

  def device_ownership_attributes=(attributes)
    dev = build_device_ownership(attributes)
    dev.user = self.user
  end
end


class DeviceOwnership < ActiveRecord::Base
  belongs_to :user  
  belongs_to :device
end

Now you can save all associations at once with in a transaction if your params are like this:

pramas = {"user"=>{ "email"=>"user@example.com", "devices_attributes" =>{"0"=>{"name" => "Devise 1", "device_ownership_attributes"=>{"device_serial_number"=>"xyz"}}}}
user = User.create(params['user'])
# will save User, devise, and devise ownership all at once.

来源：https://stackoverflow.com/questions/25941440/how-to-pass-data-to-join-table-on-creation