限制has_many与mongoid关联中的对象数 [英] Limit number of objects in has_many association with mongoid

问题描述

我想限制帖子和图片之间has_many关联中关联对象的数量:

I want to limit the number of associated objects in a has_many association between a post and pictures :

在活动记录中，我可以做类似的事情

In active record i can do something like

class post < < ActiveRecord::Base
  has_many :pictures, :limit => 2
end

但是mongoid提出了一个带有限制的异常:

But mongoid raise an exception with limit:

为关系:picture提供的无效选项:limit.有效选项 是:as，自动保存，从属，foreign_key，order，class_name，extend， inverse_class_name，inverse_of，名称，关系，验证. (Mongoid :: Errors :: InvalidOptions)

Invalid option :limit provided to relation :pictures. Valid options are: as, autosave, dependent, foreign_key, order, class_name, extend, inverse_class_name, inverse_of, name, relation, validate. (Mongoid::Errors::InvalidOptions)

是否存在另一种实现relize:limit的实现?

Is there an alternative implementation to relize :limit?

推荐答案

实际上并没有限制关联中的对象数量，它只是限制了查询关系时返回的结果数量.您可能想要这样的答案限制has_many关联中的对象数量-将向您展示如何在验证过程中检查关联对象的数量.

using has_many :limit doesn't actually restrict the number of objects in the association -- it just limits the number of results returned when querying the relation. You probably want something like this answer Limit number of objects in has_many association -- which will show you how to check the number of assocated objects during validation.

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