Sort Embedded Documents in Array and fetch specifics - node.js

Question

I have a mongoose model like this:
var activityItem = mongoose.Schema({
timestampValue: Number,
xabc: String,
full: Boolean,
comp: Boolean
});
var ABC = mongoose.Schema({
activity: [activityItem],
user: {
type: mongoose.Schema.ObjectId,
ref: 'User'
},
username: String
});
I want to get the activityItem array elements that have a timestampValue less than a specific value. Also, I want to sort the activity array first according to the timestampValue
This is the code that I currently have. And it doesn't work.
UserActivity.findOne({
'user': current_user,
'activity' : {
$all: [
{
"$elemMatch": {
timestampValue: {
$lte: time
}
}
}
]
}
},
function(err, user){
})
Sample Document structure:
{
"_id" : ObjectId("56d5e88adfd14baf1848a7c6"),
"user" : ObjectId("56bf225342e662f4277ded73"),
"notifications" : [],
"completed" : [],
"activity" : [
{
"timestampValue": 1456902600000,
"xabc": "Some value",
"full": true,
"comp": false,
"_id" : ObjectId("56d5e88adfd14baf1848a7d2")
},
{
"timestampValue": 1456702600000,
"xabc": "Some other value",
"full": true,
"comp": false,
"_id" : ObjectId("56d5e88adfd14baf1848a7d3")
}
],
"__v" : 1
}
The POST call has the following params
hash: "2e74aaaf42aa5ea733be963cb61fc5ff"
time: 1457202600000
hash comes into the picture once i have the docs from mongo
time is a unix timestamp value.
Instead of returning only the elements that are less than the time value, it is returning all the array elements. I tried the aggregation framework to sort the array before querying, but couldn't get the hang of it.
Any help would be greatly appreciated.

Answer 1

Please try to do it through aggregation as below
ABS.aggregate([
// filter the document by current_user
{$match: {user: ObjectId(current_user)}},
// unwind the activity array
{$unwind: '$activity'},
// filter the timestampValue less than time
{$match: {'activity.timestampValue': {$lte: time}}},
// sort activity by timestampValue in ascending order
{$sort: {'activity.timestampValue': 1}},
// group by _id, and assemble the activity array.
{$group: {_id: '$_id', user: {$first: '$user'},activity: {$push: '$activity'}}}
], function(err, results){
if (err)
throw err;
// populate user to get details of user information if needed
//ABS.populate( results, { "path": "user" }, function(err, rets) {
//
//});
});

Answer 2

Well, it seems little bit tricky with MongoDb aggregation pipeline unless you have MongoDB 3.2, but you can definitely
achieve your result with help of map-reduce.
e.g.
MongoDB version < 3.2
var findActivities = function (time) {
db.col.mapReduce(function () {
var item = Object.assign({}, this);
delete item.activity;
item.activity = [];
for (var i = 0; i < this.activity.length; i++) {
if (this.activity[i].timestampValue <= time) {
item.activity.push(this.activity[i]);
}
}
emit(item._id, item);
}, function (k, v) {
return {items: v};
}, {
out: {"inline": true},
scope: {time: time}
}).results.forEach(function (o) {
printjson(o); // Or perform action as appropriate
});
};
Based your sample data when called findActivities(1456802600000), it will find and return only those documents matching criteria.
{
"_id" : ObjectId("56d5e88adfd14baf1848a7c6"),
"value" : {
"_id" : ObjectId("56d5e88adfd14baf1848a7c6"),
"user" : ObjectId("56bf225342e662f4277ded73"),
"notifications" : [
],
"completed" : [
],
"__v" : NumberInt(1),
"activity" : [
{
"timestampValue" : NumberLong(1456702600000),
"xabc" : "Some other value",
"full" : true,
"comp" : false,
"_id" : ObjectId("56d5e88adfd14baf1848a7d3")
}
]
}
}
MongoDB version 3.2+
db.col.aggregate([
{$project:{user:1, notifications:1, completed:1, activity:{
$filter:{input: "$activity", as: "activity", cond:{
$lte: ["$$activity.timestampValue", 1456802600000]}}}}}
])
Both solutions will have same output.