获取“上一个”带有 mongoId 的文档

发布于 2024-10-26 04:42:00 字数 742 浏览 1 评论 0原文

我将 Images 存储在 mongoDB 中。它们按“created_at”排序。

现在，当我使用 Image.find("documentID") 加载单个项目时，我想根据 created_at 访问该文档之前的文档和之后的文档> 订单。

为此，我在 image.rb 中有两种方法和一个 default_scope：

default_scope asc(:created_at)     

def previous_image
  self.class.last(:conditions => {:created_at.lt => created_at})
end

def next_image
  self.class.first(:conditions => {:created_at.gt => created_at})
end

mongoDB 中是否有本地方法来访问当前文档之前和之后的文档？

是否有更好的方法在 Rails 中使用 mongoID 创建此类命名范围来访问上一个和下一个项目，同时考虑性能（不要对一张图像查询三次）？

编辑：“previous_image”应该使用最后一个，而不是第一个。这解决了“跳过”项目的错误。不过，关于实现这一目标的正确方法的问题仍然存在。

原文

I have Images stored in mongoDB. They are sorted by "created_at".

Now, when I load a single item with Image.find("documentID") I want to access the document just before and the one just after this one, based on the created_at order.

For that, I have two methods and a default_scope in image.rb:

default_scope asc(:created_at)     

def previous_image
  self.class.last(:conditions => {:created_at.lt => created_at})
end

def next_image
  self.class.first(:conditions => {:created_at.gt => created_at})
end

Is there a native way in mongoDB to access the document before and after the current document?

Is there a better way to create such named scopes with mongoID in rails to access previous and next items, also considering performance (not querying three times for one image)?

Edit: The "previous_image" should use last, not first. That solves the bug of "skipping" items. The questions about the proper way to achive this remain, though.

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埖埖迣鎅 2024-11-02 04:42:00

您可以尝试这样的方法：

def previous_image mongoid
  self.class.find(:conditions => {:_id => {$lt: mongoid}}).sort({:_id=>-1}).limit(1)
end

def next_image mongoid
  self.class.find(:conditions => {:_id => {$gt: mongoid}}).sort({:_id=>1}).limit(1)
end

这种方法利用 Mongo id 的顺序。

You may try something like this:

def previous_image mongoid
  self.class.find(:conditions => {:_id => {$lt: mongoid}}).sort({:_id=>-1}).limit(1)
end

def next_image mongoid
  self.class.find(:conditions => {:_id => {$gt: mongoid}}).sort({:_id=>1}).limit(1)
end

This approach utilizes sequentiality of Mongo ids.

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五里雾 2024-11-02 04:42:00

您可以根据 jhavdra 的响应尝试类似以下内容，但针对 Mongoid 语法进行了重写。

def previous_image
  self.class.where(:_id.lt => self._id).order_by([[:_id, :desc]]).limit(1).first
end

def next_image
  self.class.where(:_id.gt => self._id).order_by([[:_id, :asc]]).limit(1).first
end

You could try something like the following, based on jhavdra's response, but rewritten for Mongoid syntax.

def previous_image
  self.class.where(:_id.lt => self._id).order_by([[:_id, :desc]]).limit(1).first
end

def next_image
  self.class.where(:_id.gt => self._id).order_by([[:_id, :asc]]).limit(1).first
end

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