Mongodb aggregation in mongo command prompt - mongodb

Question

I have the following code based upon this question
How to efficiently perform "distinct" with multiple keys?:
collection = db.products;
result = collection.aggregate(
[
{"$group": { "_id": { "P1 Connection": "$p1c", "P1 Size": "$p1s" } } },
{"$match" : {"parentGUID":ObjectId("5509b246c519ce4b900138a3")}}
]
)
printjson(result);
The printjson statement only prints a bunch of code, and not an object. I also tried result() but that got the following error:
> result()
2015-10-29T10:31:14.892-0400 TypeError: Property 'result' of object #<Object> is not a function
How do I get the results of this aggregation? It looks like it may be possible to do this if I put my code in a file and run that, but I am having a hard time believing that there is no quick and dirty way to run this query in the mongodb command prompt.

Answer 1

Move the $match pipeline step to the very beginning, this will filter the documents that get into the pipeline and the $group pipeline stage will then run the pipeline with the correct documents. Since MongoDB 2.6 adds support for returning a cursor for the aggregate() method, you would need to iterate over the cursor using the forEach() method and access the documents, as in the following example:
var pipeline = [
{"$match" : {"parentGUID":ObjectId("5509b246c519ce4b900138a3")}},
{"$group": { "_id": { "P1 Connection": "$p1c", "P1 Size": "$p1s" } } }
];
var results = db.products.aggregate( pipeline );
results.forEach(printjson);