accepts_nested_attributes_forで指定した関連先のvalidationに自身のidがpresence: trueだとnested_formが使えない件Rails class User < ActiveRecord::Base has_many :memberships has_many :groups, through: :memberships end class Membership < ActiveRecord::Base belongs_to :user belongs_to :group validates :user_id, presence: true validates :group_id, presence: true end class Group < ActiveRecord::Base has_many :memberships accep