在rails3中创建新记录之前如何检查记录是否存在? [英] How to check if a record exists before creating a new one in rails3?

问题描述

这是我想要完成的:

• 我有一个标记系统.
• 创建帖子时创建标签(帖子 has_many :tags, :through => :tag_joins.
• 当使用标签创建帖子时，会自动创建标签连接).

我想检查标签是否已经存在.如果确实如此，我想将现有标签用于 tag_join 记录，而不是创建新的标签记录.

I want to check if the tag already exists. If it does I want to use the existing tag for the tag_join record, rather than creating a new tag record.

这是我当前的代码，它不起作用.

Here is my current code, which isn't working.

class Tag < ActiveRecord :: Base
  belongs_to :user
  belongs_to :tag_join
  belongs_to :post

  before_create :check_exists

  def check_exists
    tag = Tag.where(:name => self.name, :user_id => current_user.id)
    if tag.nil?
      tag = Tag.create(:name => self.name, :user_id => current_user.id)
    end
  end

end

但这不起作用，我在创建任务时遇到错误...(服务器实际上只是超时 - 我没有收到特定错误).

This doesn't work though, I'm getting an error upon task creation...(the server is actually just timing out - I don't receive a specific error).

有什么想法吗?

Tokland 说我通过告诉它再次创建标签来创建一个无限循环 - 所以我尝试了这个:

Tokland said I was creating an infinite loop by telling it to create tag again - so I tried this:

 def check_exists
      tag = Tag.find_by_name_and_user_id(:name => self.name, :user_id => current_user.id)
      if tag != nil
        self.id = tag.id
      end
  end

仍然得到服务器超时

我不确定这是否重要，但添加标签的方式类似于http://railscasts.com/episodes/73-complex-forms-part-1

I'm not sure if this matters, but the way the tags are being added is similar to "http://railscasts.com/episodes/73-complex-forms-part-1

它们嵌套在帖子表单中，并使用如下内容:

they're nested in the post form, and use something like this:

def tag_attributes=(tag_attributes)
  tag_attributes.each do |attributes|
    tags.build(attributes)
  end
end

我想知道这是否会阻止整个工作?此外，在模型中使用 current_user.id 似乎肯定是一个问题...

I'm wondering if this is stopping this whole thing from working? Also, using current_user.id in the model definitely seems to be an issue...

我发现了一些东西:这必须改变，我们之前使用的格式是不正确的语法 - 通常用于 .where 方法.

Something I have figured out: this had to change, the format we were using before was incorrect syntax - generally used for a .where method.

  def check_exists
     @tag = Tag.find_by_name_and_user_id(self.name, self.user_id) 
     if @tag != nil
       #return false
       #self=@tag
     end
  end

现在的问题是，我可以知道标签是否已经存在.但是然后呢?如果我使用 return false 选项，则创建帖子时会出现错误，并且不会创建连接记录...另一个选项self=@tag"显然不起作用.

The problem now is this, I can learn if it the tag already exists. But then what? If I go with the return false option, there is an error upon post creation, and the join record isn't created... The other option "self=@tag" obviously just doesn't work.

推荐答案

您会发现很难从 Tag 模型中做到这一点.似乎您想要的是使用嵌套属性更新 Post，如下所示:

You're going to find it hard to to this from within the Tag model. It seems like what you want is to update the Post using nested attributes, like so:

post = Post.create
post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})

通过使用虚拟属性设置器方法，这实际上非常简单:

This is actually pretty simple to do by using a virtual attribute setter method:

class Post < AR::Base
  has_many :tags

  def tags_attributes=(hash)
    hash.each do |sequence,tag_values|
      tags <<  Tag.find_or_create_by_name_and_user_id(tag_values[:name],\
        tag_values[:user_id])
    end
  end

> post = Post.create
> post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})
> Tag.count # => 1
# updating again does not add dups
> post.update_attributes(:tags_attributes=>{"0"=>{:name=>"fish",:user_id=>"37"}})
> Tag.count # => 1

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