MongoDB querying by sub-document value not working as expected - mongodb

Question

I have two schemas, a Profile and a LevelOfNeed.
Profile
{
"_id" : ObjectId("56d35960a695dfa140137fca"),
. . .
"levelOfNeedServiced" : ObjectId("56d35828a695dfa140137fc7")
}
Level of Need
{
"_id" : ObjectId("56d35828a695dfa140137fc7"),
"sortOrder" : 2,
"description" : "Moderate Needs",
"additionalCost" : 3,
"__v" : 0
}
I currently have 4 documents for LevelOfNeed. What I need to do is select all of the Profile documents where the levelOfNeedServiced.sortOrder is >= a value.
Example:
db.getCollection('profiles').find({
'levelOfNeedServiced.sortOrder': { $gte: 2 }
})
Given my data, I would expect to see the example Profile, but this returns no results. What am I doing wrong?
Update 1
Previously, I was running MongoDB 3.0.9. I've since upgraded to 3.2.3, however I'm still getting the same results. According to the docs, I should be able to query on an embedded document field value.
Update 2
The aggregate function solution works as expected, but since I already had an array of LevelOfNeed objects, I was able to use that to get to the related documents I needed using the $in operator.

Answer 1

Unfortunately mongodb does not support joins until version 3.2. In version 3.2 it provides the $lookup aggregation operator to lookup referenced documents across collections.
You could use it as below:
db.Profile.aggregate([
{
$lookup:{
"from":"LevelOfNeed",
"localField":"levelOfNeedServiced",
"foreignField":"_id",
"as":"joined"
}
},
{
$match:{
"joined.sortOrder":{$gte:2}
}
},
{
$project:{"levelOfNeedServiced":1,...} //include things you want to project.
}
])
Your code:
db.getCollection('profiles').find({
'levelOfNeedServiced.sortOrder': { $gte: 2 }
})
does not work as intended because, the field levelOfNeedServiced is identified as a field containing an ObjectId and not the resolved LevelOfNeed document.