Rails 2.3.3及以下版本

摘自ActiveRecord CHANGELOG(v1.12.0, 2005年10月16日):

引入只读记录。如果你调用object.readonly!那么它就会 将对象标记为只读并引发 ReadOnlyRecord如果你呼叫 object.save。object.readonly吗?报告 对象是否只读。 传递:readonly => true to any 查找器方法将标记返回 记录为只读。:加入 选项现在暗示:readonly，所以如果 您使用此选项，保存相同的内容 记录现在将失败。使用find_by_sql 四处工作。

使用find_by_sql并不是一个真正的替代方案，因为它返回原始的行/列数据，而不是ActiveRecords。你有两个选择:

在记录中强制实例变量@readonly为false (hack) 使用:include =>:card代替:join =>:card

Rails 2.3.4及以上版本

在2012年9月10日之后，上述大部分都不再成立:

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.)

要解除它…

module DeactivateImplicitReadonly
  def custom_join_sql(*args)
    result = super
    @implicit_readonly = false
    result
  end
end
ActiveRecord::Relation.send :include, DeactivateImplicitReadonly

Rails 2.3.3及以下版本

摘自ActiveRecord CHANGELOG(v1.12.0, 2005年10月16日):

引入只读记录。如果你调用object.readonly!那么它就会 将对象标记为只读并引发 ReadOnlyRecord如果你呼叫 object.save。object.readonly吗?报告 对象是否只读。 传递:readonly => true to any 查找器方法将标记返回 记录为只读。:加入 选项现在暗示:readonly，所以如果 您使用此选项，保存相同的内容 记录现在将失败。使用find_by_sql 四处工作。

使用find_by_sql并不是一个真正的替代方案，因为它返回原始的行/列数据，而不是ActiveRecords。你有两个选择:

在记录中强制实例变量@readonly为false (hack) 使用:include =>:card代替:join =>:card

Rails 2.3.4及以上版本

在2012年9月10日之后，上述大部分都不再成立:

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.)

select('*')似乎在Rails 3.2中解决了这个问题:

> Contact.select('*').joins(:slugs).where('slugs.slug' => 'the-slug').first.readonly?
=> false

为了验证，省略select('*')确实会产生只读记录:

> Contact.joins(:slugs).where('slugs.slug' => 'the-slug').first.readonly?
=> true

我不能说我理解其中的原理，但至少这是一个快速而干净的解决方法。

这可能在最近的Rails版本中有所改变，但解决这个问题的适当方法是在find选项中添加:readonly => false。

而不是find_by_sql，你可以在查找器上指定一个:select，一切都很愉快…

start_cards = DeckCard。发现:, :select => 'deck_cards.*'， :joins => [:card]， :conditions => ["deck_cards.deck_id = ? "和卡片。Start_card = ?"， @game.deck.id, true]