Get single array from mongoDB collection where the status is current - mongodb

Question

i want to find accepted bodypart which have status active
i tried this
db.patients.find({
"injury.injurydata.injuryinformation.dateofinjury": {
"$gte": ISODate("2014-05-21T08:00:00Z") ,
"$lt": ISODate("2014-06-03T08:00:00Z")
},
{
"injury.injurydata.acceptedbodyparts":1,
"injury.injurydata.injuryinformation.dateofinjury":1
"injury":{
$elemMatch: {
"injury.injurydata.acceptedbodyparts.status": "current"
}
}
})
but still get both array

Answer 1

If acceptedbodyparts is an array, you can't query acceptedbodyparts.status. If status is a field on the documents contained in the array, you would need to use another $elemMatch clause in your query. So the last part would look something like this:
{"injury":{ "$elemMatch": { "injurydata.acceptedbodyparts": {"$elemMatch": {"status":"current"} }} }}
I also removed the injury. prefix in the first $elemMatch because you're querying data within the injury array.
Note that this will return the entire document with the full array, as long as it contains the document you're searching for. If your intention is to retrieve a particular element in an array, $elemMatch is the wrong approach.

Answer 2

Standard projection will not work with nested arrays or limiting any fields inside arrays. For that you need the aggregation framework:
db.patients.aggregate([
// First match, Matches documents
{ "$match": {
"injury.injurydata.injuryinformation.dateofinjury": {
"$gte": ISODate("2014-05-21T08:00:00Z"),
"$lt": ISODate("2014-06-03T08:00:00Z")
}
}},
// Un-wind the arrays
{ "$unwind": "$injury" },
{ "$unwind": "$injury.injurydata" },
{ "$unwind": "$injury.injurydata.acceptedbodyparts" },
// Now match the required data in the array
{ "$match": {
"injury.injurydata.acceptedbodyparts.status": "current"
}},
// Group only wanted fields
{ "$group": {
"_id": "$_id",
"acceptedbodyparts": {
"$push": "injury.injurydata.acceptedbodyparts"
}
}}
])
You can add in other fields outside of the array either using $first or by akin g them part of the _id in the grouping.
This is just something that is outside of the scope of the standard projection available and the aggregation framework with the extended manipulation capabilities solves this.