不能破坏多对多关系中的记录 [英] Can't destroy record in many-to-many relationship

问题描述

我是Rails的新手，所以我确定我犯了一个简单的错误.

I'm new to Rails, so I'm sure I've made a simple mistake.

我已经在两个模型之间建立了多对多关系:User和Group.它们通过结点模型GroupMember连接起来.

I've set up a many-to-many relationship between two models: User and Group. They're connected through the junction model GroupMember.

这是我的模型(删除了无关的内容):

Here are my models (removed irrelevant stuff):

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的"Active Record Associations"指南).

The table for GroupMembers contains additional information about the relationship, so I didn't use has_and_belongs_to_many (as per the Rails "Active Record Associations" guide).

我遇到的问题是我无法销毁GroupMember.

The problem I'm having is that I can't destroy a GroupMember.

这是Rails控制台的输出:

Here's the output from rails console:

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，所以任何帮助将不胜感激.

This is driving me crazy, so any help would be greatly appreciated.

推荐答案

当您从HABTM关系切换为has_many:through关系时，您似乎忘记了添加id列.活动记录需要GroupMember具有.destroy的ID才能正常工作.

When you switched from the HABTM relationship to a has_many :through relationship it looks like you may have forgotten to add back the id column. Active record needs GroupMember to have an id for .destroy to work like that.

在迁移中查找:id => false并摆脱它.然后重做迁移.

Look for the :id => false in your migration and get rid of it. then redo the migration.

希望有帮助.

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