[英]Mongoid - querying by referenced document
I have a model named Ad which looks like this: 我有一个名为Ad的模型,如下所示:
class Ad
include Mongoid::Document
referenced_in :category
end
and Category model: 和类别模型:
class Category
include Mongoid::Document
referenced_in :domain
references_many :ads
end
How can I select Ads by domain? 如何按域选择广告? I have tried to use
Ad.where('category.domain_id' => domain.id)
but this does not work. 我曾尝试使用
Ad.where('category.domain_id' => domain.id)
但这不起作用。
The problem is that MongoDB doesn't have any way of mapping a Category
record to an Ad
record. 问题是MongoDB没有任何方法将
Category
记录映射到Ad
记录。 All it knows is that an Ad
record has a category_id
field so 'category.domain_id'
will always return nothing. 它只知道
Ad
记录有一个category_id
字段,因此'category.domain_id'
将始终不返回任何内容。 The dot notation inside queries works only for embedded documents, not references (which are still second-class citizens in MongoDB). 查询中的点表示法仅适用于嵌入式文档,而不适用于引用(它们仍然是MongoDB中的二等公民)。
So to solve your problem, you'll need 2 queries: 因此,要解决您的问题,您需要2个查询:
category_ids = Category.where(:domain_id => domain.id).map(&:_id)
Ad.where(:category_id.in => category_ids)
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