Rails：ActiveRecord::HasManyThroughSourceAssociationNotFoundError：找不到源关联

Question

我有以下代码（有点简化...

create_table :signatures do |t|
  t.integer :signer_id
  t.integer :card_id

  t.timestamps
end

模型看起来像......

class Signature < ActiveRecord::Base
    belongs_to :card
    belongs_to :user
end

class Card < ActiveRecord::Base
    has_many :signatures
    has_many :signers, :through => :signatures, :foreign_key => "card_id"
end


class User < ActiveRecord::Base

    has_many :sent_cards, :class_name => "Card", :foreign_key => "sender_id"
    has_many :received_cards, :class_name => "Card", :foreign_key => "recipient_id"

    has_many :signatures
    has_many :signed_cards, :through => :signatures, :foreign_key => "signer_id"

end

我在使用 rails 控制台时看到以下错误...

ruby-1.9.2-p0 > u15.signed_cards
ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s) :signed_card or :signed_cards in model Signature. Try 'has_many :signed_cards, :through => :signatures, :source => <name>'. Is it one of :card or :user?
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/reflection.rb:517:in `check_validity!'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/associations/association.rb:27:in `initialize'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/associations/collection_association.rb:24:in `initialize'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/associations.rb:164:in `new'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/associations.rb:164:in `association'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.1.0/lib/active_record/associations/builder/association.rb:41:in `block in define_readers'
    from (irb):11
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.1.0/lib/rails/commands/console.rb:45:in `start'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.1.0/lib/rails/commands/console.rb:8:in `start'
    from /home/slabounty/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.1.0/lib/rails/commands.rb:40:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

当我添加 source => :card/:user 时，我得到了同样的结果（我相信在这种情况下应该是 :card）。

有什么想法我在这里做错了吗？

---

显示部分解决方案，因为我想清理 几样东西。迁移与以前的版本保持一致。我现在 看到在签名中找不到 user_id 的 SQL 错误（见下文）。一世 不想这么说，但大多数时候我一直在输入 :foreign_key 任何我想的地方 他们可能无济于事。

    class Signature < ActiveRecord::Base
        belongs_to :card
        belongs_to :signer, :class_name => "User"
    end


    class Card < ActiveRecord::Base
        # Correct
        has_many :signatures
        has_many :signers, :through => :signatures, :source => :user

    end

    class User < ActiveRecord::Base
        # Wrong!
        has_many :signatures, :foreign_key => "signer_id"
        has_many :signed_cards, :through => :signatures, :source => :card
    end

出现错误（减去堆栈跟踪）

ruby-1.9.2-p0 >   u15.signed_cards
  Card Load (0.5ms)  SELECT "cards".* FROM "cards" INNER JOIN "signatures" ON "cards"."id" = "signatures"."card_id" WHERE "signatures"."user_id" = 15 ORDER BY cards.created_at DESC
SQLite3::SQLException: no such column: signatures.user_id: SELECT "cards".* FROM "cards" INNER JOIN "signatures" ON "cards"."id" = "signatures"."card_id" WHERE "signatures"."user_id" = 15 ORDER BY cards.created_at DESC
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: signatures.user_id: SELECT "cards".* FROM "cards" INNER JOIN "signatures" ON "cards"."id" = "signatures"."card_id" WHERE "signatures"."user_id" = 15 ORDER BY cards.created_at DESC

Card.signers 按预期返回一个空数组。

仍在寻求这方面的帮助。在您不使用相同名称的情况下，我无法以简单、直接的解释方式找到很多内容（即您需要一个 foreign_key 和 source。

Answer 1

好的，既然我在这方面遇到了这么大的困难，我想向大家展示一下 最终版本的样子。我过得如此艰难的很大一部分原因 解决这个问题的事实是，rails 控制台似乎不是 在我进行更改时正确重新加载内容。我没有意识到这一点，直到我 放弃了一晚，第二天早上回来，那个案子 前一天晚上没有工作，而没有工作的情况是。

迁移是一样的，但为了完整起见，我会重复一遍。

def change
    create_table :signatures do |t|
        t.integer :signer_id
        t.integer :card_id
        t.boolean :signed,    :default => false
        t.text :message

        t.timestamps
    end
end

Signature 类有两个belongs_to 与card 的情况是 通常会在示例中显示，并且签名者是用户类型。

class Signature < ActiveRecord::Base
    belongs_to :card
    belongs_to :signer, :class_name => "User"
end

用户有很多签名（即使你不直接使用也是必要的） dmany signed_cards 通过带有卡源的签名（告诉 Rails signed_cards 是哪个类类型。

class User < ActiveRecord::Base
    has_many :signatures, :foreign_key => "signer_id"
    has_many :signed_cards, :through => :signatures, :source => :card 
end

最后，卡片有很多签名（再次需要）和很多签名者 通过签名和signer_id的签名者的foreign_key。

class Card < ActiveRecord::Base
    has_many :signatures
    has_many :signers, :through => :signatures, :foreign_key => 'signer_id'
end

希望这将帮助其他遇到类似问题的人。

Answer 2

用户应该这样定义：

class User < ActiveRecord::Base

  has_many :sent_cards, :class_name => "Card", :foreign_key => "sender_id"
  has_many :received_cards, :class_name => "Card", :foreign_key => "recipient_id"

  has_many :signatures
  has_many :signed_cards, :through => :signatures, :source => :card

end

当您的关联名称与 :through 中使用的名称不同时，您必须定义 source 参数。如果您查看异常消息，它明确要求您这样做。