has_many autosave_associated_records_for_*

Question

我正在尝试关联现有记录，同时仍然可以添加新记录。以下代码不起作用，但非常接近我需要的内容。如何完成关联已有记录和创建新记录？

has_many :comments, :through => :commentings, :source => :commentable, :source_type => "Comment"
accepts_nested_attributes_for :comments, :allow_destroy => true

def autosave_associated_records_for_comments
  comments.each do |comment|
    if existing_comment = Comment.find_by_fax_and_name(comment.fax, comment.name)
      self.comments.reject! { |hl| hl.fax == existing_comment.fax && hl.name == existing_comment.name }
      self.comments << existing_comment
    else
      self.comments << comment
    end
  end
end

这里有一行相关的源代码：https://github.com/rails/rails/blob/v3.0.11/activerecord/lib/active_record/autosave_association.rb#L155

Answer 1

我已经做了一个解决方案，但是如果你知道更好的方法，请让我知道！

def autosave_associated_records_for_comments
  existing_comments = []
  new_comments = []

  comments.each do |comment|
    if existing_comment = Comment.find_by_fax_and_name(comment.fax, comment.name)
      existing_comments << existing_comment
    else
      new_comments << comment
    end
  end

  self.comments << new_comments + existing_comments
end

Answer 2

我有一个标签系统，它利用了has_many :through关系。这里的两个解决方案都没有让我达到我需要的程度，所以我想出了一个可能对其他人有帮助的解决方案。这已经在Rails 3.2上进行了测试。

设置

以下是我的模型的基本版本：

Location对象：

class Location < ActiveRecord::Base
    has_many :city_taggables, :as => :city_taggable, :dependent => :destroy
    has_many :city_tags, :through => :city_taggables

    accepts_nested_attributes_for :city_tags, :reject_if => :all_blank, allow_destroy: true
end

标记对象

class CityTaggable < ActiveRecord::Base
   belongs_to :city_tag
   belongs_to :city_taggable, :polymorphic => true
end

class CityTag < ActiveRecord::Base
   has_many :city_taggables, :dependent => :destroy
   has_many :ads, :through => :city_taggables
end

解决方案

我确实覆盖了autosave_associated_record_for方法，如下所示：

class Location < ActiveRecord::Base
   private

   def autosave_associated_records_for_city_tags
     tags =[]
     #For Each Tag
     city_tags.each do |tag|
       #Destroy Tag if set to _destroy
       if tag._destroy
         #remove tag from object don't destroy the tag
         self.city_tags.delete(tag)
         next
       end

       #Check if the tag we are saving is new (no ID passed)
       if tag.new_record?
         #Find existing tag or use new tag if not found
         tag = CityTag.find_by_label(tag.label) || StateTag.create(label: tag.label)
       else
         #If tag being saved has an ID then it exists we want to see if the label has changed
         #We find the record and compare explicitly, this saves us when we are removing tags.
         existing = CityTag.find_by_id(tag.id)
         if existing    
           #Tag labels are different so we want to find or create a new tag (rather than updating the exiting tag label)
           if tag.label != existing.label
             self.city_tags.delete(tag)
             tag = CityTag.find_by_label(tag.label) || CityTag.create(label: tag.label)
           end
         else
           #Looks like we are removing the tag and need to delete it from this object
           self.city_tags.delete(tag)
           next
         end
       end
       tags << tag
     end
     #Iterate through tags and add to my Location unless they are already associated.
     tags.each do |tag|
       unless tag.in? self.city_tags
         self.city_tags << tag
       end
     end
   end

上面的实现按照我在嵌套表单中使用fields_for时所需的方式保存、删除和更改标签。如果有简化的方法，我愿意接受反馈。需要指出的是，我是在标签更改时显式地更改标签，而不是更新标签。

Answer 3

在Rails6(可能还有更早的版本)中，很容易覆盖由accepts_nested_attributes_for生成的属性编写器并使用find_or_initialize_by。

在这种情况下，您可以简单地编写：

has_many :comments, :through => :commentings, :source => :commentable, :source_type => "Comment"
accepts_nested_attributes_for :comments, :allow_destroy => true

def comments_attributes=(hashes)
  hashes.each { |attributes| comments << Comment.find_or_initialize_by(attributes)
end

我还没有在传递:id或:_destroy密钥时测试过这一点，因为它不适用于我的情况，但是如果你这样做了，请随时分享你的想法或代码。

我希望看到Rails原生地实现这一点，也许是通过向accepts_nested_attributes_for传递一个upsert: true选项。