以参照物为标准的蒙古范围 [英] mongoid scope with referenced object as criteria

问题描述

在Rails 3中，我对Mongoid模型有以下范围:

I have following scope for Mongoid model in Rails 3:

class Expert
  include Mongoid::Document
  referenced_in :category

   scope :currently_available, lambda { |category, limit|
    limit ||= 5
    {
      :where => {:category => category, :state => 'available'}, 
      :limit => limit
    }
  }

category这是引用模型的一个实例:

category here is an instance of referenced model:

class Category
  include Mongoid::Document
  references_many :experts, :inverse_of => :category

当我将范围称为Expert.currently_available(Category.first, 5)时，我得到了一个Criteria对象:

When I call the scope as Expert.currently_available(Category.first, 5), I got a Criteria object:

ruby-1.9.2-p136 :110 > Expert.currently_available(Category.first, 5)
 => #<Mongoid::Criteria
  selector: {:category=>#<Category _id: 4d95ea8773fdea4c47000003, _type: nil, _id: BSON::ObjectId('4d95ea8773fdea4c47000003'), title: "Tax Advisors", price: 5.5>, :state=>"available"},
  options:  {:limit=>5},
  class:    Expert,
  embedded: false>

问题是:如何在此条件下加载收藏集?当我做.to_a时，它说:
Cannot serialize an object of class Category into BSON

Question is: How can I load a collection within this criteria? When I do .to_a, it says:
Cannot serialize an object of class Category into BSON

直接拾取类别时，类别本身是有效的BSON obj，但在范围上无法呈现引用的obj.

Category itself is valid BSON obj when picked up directly, but in scope it fails to render referencing obj.

提前谢谢！

推荐答案

这对我有用(Mongoid 2.0):

This works for me(Mongoid 2.0):

:where => {:category_id => category.id, :state => 'available'}

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