Question

我是Rails的新手，所以我确信我犯了一个简单的错误。

我在两个模型之间建立了多对多关系：User和Group。它们通过联结模型GroupMember连接。

以下是我的模型（删除不相关的内容）：

class User < ActiveRecord::Base
  has_many :group_members
  has_many :groups, :through => :group_members
end

class GroupMember < ActiveRecord::Base
  belongs_to :group
  belongs_to :user
end

class Group < ActiveRecord::Base
  has_many :group_members
  has_many :users, :through => :group_members
end

GroupMembers的表包含有关关系的其他信息，因此我没有使用has_and_belongs_to_many（根据Rails“Active Record Associations”指南）。

我遇到的问题是我无法销毁GroupMember。

以下是rails console的输出：

irb(main):006:0> m = GroupMember.new
=> #<GroupMember group_id: nil, user_id: nil, active: nil, created_at: nil, updated_at: nil>
irb(main):007:0> m.group_id =1
=> 1
irb(main):008:0> m.user_id = 16
=> 16
irb(main):009:0> m.save
=> true
irb(main):010:0> m.destroy
NoMethodError: undefined method `eq' for nil:NilClass
    from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/whiny_nil.rb:48:in `method_missing'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/persistence.rb:79:in `destroy'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/locking/optimistic.rb:110:in `destroy'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy'
    from /usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.4/lib/active_support/callbacks.rb:413:in `_run_destroy_callbacks'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/callbacks.rb:260:in `destroy'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:292:in `with_transaction_returning_status'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:139:in `transaction'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:207:in `transaction'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:290:in `with_transaction_returning_status'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-3.0.4/lib/active_record/transactions.rb:235:in `destroy'
    from (irb):10

这让我发疯，所以任何帮助都会非常感激。

Answer 1

当您从HABTM关系切换到has_many：through关系时，您可能忘记添加回id列。活动记录需要GroupMember具有.destroy的id才能像这样工作。

在迁移中查找:id => false并删除它。然后重做迁移。

希望有所帮助。

Answer 2

您是否尝试过m.reload.destroy代替m.destroy，看看会发生什么？

Answer 3

我认为数据库中的group_members表没有主键。也许你没有设置它。因此，当您创建一个新的GroupMember对象并保存它时，它将没有id。您无法销毁没有id（主键）的对象。

Answer 4

我遇到了你所描述的同样的问题，你的帖子让我进一步寻找解决方案。这是我发现的：

1-从http://compositekeys.rubyforge.org/获取此复合主键库 2-将其添加到您的gem文件中 3-将以下内容添加到GroupMember set_primary_keys [：user_id，：group_id]

注意set_primary_keys而不是set_primary_key

当您调用GroupMember.primary_key时，这将返回正确的主要内容当destroy查找.primary_key时，它现在会找到它。

在您的控制台中尝试： gm = GroupMember.first gm.destroy

我希望这有助于=）

Answer 5

如果您使用关联并且出于任何原因选择不使用Active Records默认ID，则可以使用“set_primary_key”设置默认ID，以便查找和销毁等方法正常工作。

class User < ActiveRecord::Base
  set_primary_key :user_primary
  has_many :group_members, :dependent => :destroy
  has_many :groups, :through => :group_members
end

class GroupMember < ActiveRecord::Base
  set_primary_key :group_member_primary
  belongs_to :group
  belongs_to :user
end

class Group < ActiveRecord::Base
  set_primary_key :group_primary
  has_many :group_members, :dependent => :destroy
  has_many :users, :through => :group_members
end

无法在多对多关系中销毁记录

5 个答案: