ruby-on-rails-3 - 如果关联存在，如何禁止删除

Question

我在两个模型之间有如下多对多关系:

#users.rb
has_many :users_to_roles
has_many :roles, through: :users_to_roles

#users_to_roles.rb
belongs_to :user
belongs_to :role

#roles.rb
has_many :users_to_roles
has_many :users, through: :users_to_roles

如果有“处于此角色”的用户，我想禁止删除角色。 Here我找到了两个应该做这项工作的人选:

:restrict_with_exception causes an exception to be raised if there are any associated records :restrict_with_error causes an error to be added to the owner if there are any associated objects

但没有关于此语法及其工作原理的示例。

你能帮忙让它生效吗:

#roles.rb
has_many :users_to_roles
has_many :users, through: :users_to_roles, dependent: restrict_with_exception

Answer 1

使用Callbacks 可以轻松完成此类操作.就我而言，我在我的模型中添加了以下方法:

# callbacks
before_destroy :check_for_users_in_this_role

def check_for_users_in_this_role
  status = true
  if self.security_users.count > 0
    self.errors[:deletion_status] = 'Cannot delete security role with active users in it.'
    status = false
  else
    self.errors[:deletion_status] = 'OK.'
  end
  status
end