Question

Been reading about map/reduce here and on other sites and I’m still not sure if it’s the right or wrong way to solve this problem.

I have three models:

User --  embeds many SearchRequests
SearchRequest -- references 1 Item
Item

What I need to do is get a bit of information from each model and then eliminate any results that don’t meet criteria. Is this a map/reduce?

The map I want:

user.email, user.name, item.name, item.amount, 
 item.url, searchRequest.amountCutoff

Then I think I’d reduce and elminate any records where:

item.amount > searchRequest.amountCutoff

The thing I’m having trouble with is how to get the item.name, item.amount in the map. This is what I have so far (map would be called on the Users collection):

map = "function() {  if (this.search_requests)
  for (var ar in this.search_requests) {

// this part needs help  ---vvvv
    var theItem= items.where(_id: this.search_requests[ar].item_id) 

    emit ( { },
     { this.email, 
       this.name, 
       this.search_requests[ar].item_id,
       this.search_requests[ar].amountCutoff, 
       theItem.name,
       theItem.amount
      }
    }
} "

^^ The syntax on that may be incorrect. I’m still learning. It almost looks like I need the mongo equivalent of LINQs range variable in there… not sure if that’s possible.

So my question: is it possible (or smart) to access another collection that isn’t the “mapping” collection in a map function?

Answer 1

AFAIK, unfortunately, map/reduce doesn’t support for more than one collection for the moment.

Since you know the criteria item.count > n, create a index on it and query out the documents. which should contains user’s reference, say userid.

which could be done by running a javascript in mongoshell or you can write code in your environment.