是什么原因造成这个的ActiveRecord :: ReadOnlyRecord错误？ [英] What is causing this ActiveRecord::ReadOnlyRecord error?

问题描述

这是继<一href="http://stackoverflow.com/questions/628000/rails-whats-wrong-with-this-multiple-join-with-conditions-on-the-associations"相对=nofollow称号=此>这个的问题之前，这是回答。其实我发现我可以删除该查询联接，所以现在的工作查询

This follows this prior question, which was answered. I actually discovered I could remove a join from that query, so now the working query is

start_cards = DeckCard.find :all, :joins => [:card], :conditions => ["deck_cards.deck_id = ? and cards.start_card = ?", @game.deck.id, true]

这似乎工作。但是，当我尝试将这些DeckCards到另一个关联，我得到的ActiveRecord :: ReadOnlyRecord错误。

This appears to work. However, when I try to move these DeckCards into another association, I get the ActiveRecord::ReadOnlyRecord error.

这里的code

for player in @game.players 
  player.tableau = Tableau.new
  start_card = start_cards.pop 
  start_card.draw_pile = false
  player.tableau.deck_cards << start_card  # the error occurs on this line
end

和相关模型（画面是餐桌上的球员卡）

and the relevant Models (tableau are the players cards on the table)

class Player < ActiveRecord::Base
  belongs_to :game
  belongs_to :user
  has_one :hand
  has_one :tableau
end

class Tableau < ActiveRecord::Base
  belongs_to :player
  has_many :deck_cards
end  

class DeckCard < ActiveRecord::Base
  belongs_to :card
  belongs_to :deck  
end

我做了类似的行动只是在此之后code，加入 DeckCards 的球员手中，而code是工作的罚款。我想，如果我需要 belongs_to的：在De​​ckCard模式画面，但它工作正常的增加了玩家的手中。我有一个 tableau_id 和 hand_id 列在DeckCard表。

I am doing a similar action just after this code, adding DeckCards to the players hand, and that code is working fine. I wondered if I needed belongs_to :tableau in the DeckCard Model, but it works fine for the adding to player's hand. I do have a tableau_id and hand_id columns in the DeckCard table.

我抬头ReadOnlyRecord在轨API，它不说远远超出了说明。

I looked up ReadOnlyRecord in the rails api, and it doesn't say much beyond the description.

推荐答案

从的ActiveRecord 更新日志 ^{（v1.12.0，2005年10月16号）}：

介绍只读记录。如果调用object.readonly！然后它会   将对象标记为只读和提高   如果调用ReadOnlyRecord   object.save。 object.readonly？报告   对象是否是只读的。   传：只读=> true以任何   finder方法将标志着返回   记录为只读。 的：加入   选项​​现在意味着：只读，因此，如果   使用此选项，保存同一个   现在的记录将失效。使用的find_by_sql   要解决。

Introduce read-only records. If you call object.readonly! then it will mark the object as read-only and raise ReadOnlyRecord if you call object.save. object.readonly? reports whether the object is read-only. Passing :readonly => true to any finder method will mark returned records as read-only. The :joins option now implies :readonly, so if you use this option, saving the same record will now fail. Use find_by_sql to work around.

使用的find_by_sql 是不是一个真正的选择，因为它返回原行/列数据，而不是 ActiveRecords 。你有两个选择：

Using find_by_sql is not really an alternative as it returns raw row/column data, not ActiveRecords. You have two options:

1. 在记录（黑客）强制实例变量 @ReadOnly 为false
2. 使用：包括=＆GT; ：卡而不是：加入=＆GT; ：卡

1. Force the instance variable @readonly to false in the record (hack)
2. Use :include => :card instead of :join => :card

2010年9月更新

上述大部分不再成立。因此，在Rails的2.3.4的和的3.0.0：

Most of the above no longer holds true. Thus, in Rails 2.3.4 and 3.0.0:

• 使用 Record.find_by_sql 是一个可行的选择
• ：只读=＆GT;真正的自动推断的仅如果：加入指定的不明确：选择 和明确（或取景范围的继承）：只读选项（参见实施在 active_record / base.rb Rails的2.3.4，或 set_readonly_option！ >在 active_record / relation.rb 和 custom_join_sql 在 > active_record /关系/ query_methods.rb Rails的3.0.0）
• 然而，：只读=＆GT;真正的总是在 has_​​and_belongs_to_many 自动推断，如果连接表已经超过了两个外键列和：加入指定不明确的：选择（即用户提供的：只读值被忽略 - 看到 finding_with_ambiguous_select？在 active_record /协会/ has_​​and_belongs_to_many_association.rb ）
• 在最后，除非处理的是一个特殊的连接表和 has_​​and_belongs_to_many ，然后 @aaronrustad 的回答只是适用罚款的Rails 2.3.4和3.0.0。
• 请的没有的使用：包括如果你想实现一个 INNER JOIN （ ：包括意味着 LEFT OUTER JOIN ，这是选择性较差，比低效率的INNER JOIN ）

• using Record.find_by_sql is a viable option
• :readonly => true is automatically inferred only if :joins was specified without an explicit :select nor an explicit (or finder-scope-inherited) :readonly option (see the implementation of set_readonly_option! in active_record/base.rb for Rails 2.3.4, or the implementation of to_a in active_record/relation.rb and of custom_join_sql in active_record/relation/query_methods.rb for Rails 3.0.0)
• however, :readonly => true is always automatically inferred in has_and_belongs_to_many if the join table has more than the two foreign keys columns and :joins was specified without an explicit :select (i.e. user-supplied :readonly values are ignored -- see finding_with_ambiguous_select? in active_record/associations/has_and_belongs_to_many_association.rb.)
• in conclusion, unless dealing with a special join table and has_and_belongs_to_many, then @aaronrustad's answer applies just fine in Rails 2.3.4 and 3.0.0.
• do not use :includes if you want to achieve an INNER JOIN (:includes implies a LEFT OUTER JOIN, which is less selective and less efficient than INNER JOIN.)

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