Get all keys in MongoMapper Model including its association

Suppose the following model :

class Product 
 include MongoMapper::Document

 key :name, String
 key :product_category_id, ObjectId

 belongs_to :product_category
end

class ProductCategory
 include MongoMapper::Document

 key :name, String, :required => true, :unique => true

 timestamps!
 userstamps!
end

I want to implement an advanced search that will inspect all value inside my Model including its all association like : I have :

• Product A data named "aLaptop" belongs_to:ProductCategory named "Notebook".
• Product B data named "aGreatNotebook" belongs_to:ProductCategory named "Notebook".

When I search with keyword named "Notebook", I want to search it to Product.name fields and also its associations which mean ProductCategory.name also. So it will returned both of that items, because Product A have ProductCategory.name "Notebook" & Product B have Product.name "aGreatNotebook" and ProductCategory "Notebook"..

How can I do this?? I've already searching for 2 days and not success until now:(.. When is in MySQL, I used join table.. But hows in MongoMapper??

Please help.. Thank you..

You can't do joins in MongoDB. So the basic idea is to get the ObjectId associated with the "Notebook" category and then to query the products where product_category is equal to notebook_id. This generally involves two queries. So that'd be something like this:

notebook_id = ProductCategory.first(:name => "Notebook")
if notebook_id
  Product.where({:product_category_id => notebook_id['_id']})
end