Using find in a array of objects Schema using Mongoose [duplicate] - node.js

Question

This question already has answers here:
Retrieve only the queried element in an object array in MongoDB collection
(18 answers)
Closed 5 years ago.
Am having the following Mongoose Schema in my Node Application
var expenseSchema = new Schema({
particular : String,
date : {type : Date, default: Date.now},
paid_by : String,
amount : Number,
month : String
});
var roomSchema = new Schema({
name: String,
admin: String,
roomies : [String],
expenses : [expenseSchema]
},{
collection : 'rooms'
});
I need to get expenses for a room for a particular month using find().
Here is what I was trying, however it returns me the whole room object
Room.findOne({_id : req.params._id, 'expenses.month' : 'oct'}).exec(function(err, result){
if(result == null) {
res.json({result : 'Oops! We couldn\'t find any rooms...'});
} else if(err) {
res.json({result : 'Error in getting Rooms'});
} else {
res.json({result : result});
}
});
Can someone help me with this?

Answer 1

You can use the positional $ operator in your projection to return the matching expenses array element in your result:
Room.findOne(
{ "_id": req.params._id, "expenses.month": "oct" },
{ "expenses.$": 1 }
).exec(callback);
or for multiple matches you could use the aggregation framework's $filter operator in the $project pipeline as:
var ObjectId = mongoose.Types.ObjectId;
Room.aggregate()
.match({ "_id": new ObjectId(req.params._id), "expenses.month": "oct" })
.project({
"expenses": {
"$filter": {
"input": "$expenses",
"as": "item",
"cond": { "$eq": [ "$$item.month", "oct" ] }
}
}
})
.exec(callback);
or if you are using an older version of Mongoose driver that does not have support for the MongoDB 3.2 $filter, you could use $map alongside $setDifference, where you can "filter" array contents without using $unwind:
var ObjectId = mongoose.Types.ObjectId;
Room.aggregate([
{ "$match": { "_id": new ObjectId(req.params._id), "expenses.month": "oct" } },
{ "$project": {
"expenses": {
"$setDifference": [
{
"$map": {
"input": "$expenses",
"as": "items",
"in": {
"$cond": [
{ "$eq": [ "$$items.month", "oct" ] },
"$$items",
false
]
}
}
},
[false]
]
}
} }
], function(err, results){
console.log(JSON.stringify(results[0], null, 4));
});

Answer 2

Assuming this can work
var expenseSchema = new Schema({
particular : String,
date : {type : Date, default: Date.now},
paid_by : String,
amount : Number,
month : String
});
var roomSchema = new Schema({
name: String,
admin: String,
roomies : [String],
expense_id : type: Schema.Types.ObjectId, ref: 'expenseSchema'
},{
collection : 'rooms'
});
Room.findOne({expense_id: req.params._id , "expenses.month": "oct" })
.populate('expense_id')
.exec(function (err, doc) {
if (err) {
throw err
}
console.log(doc)
})

Answer 3

Room.findOne({
_id : req.params._id,
'expenses.month':'oct'
},{
'expenses': {
$elemMatch:{
'month':'oct'
}
}
).exec(
function(err, result){
if(result == null) {
res.json({result : 'Oops! We couldn\'t find any rooms...'});
} else if(err) {
res.json({result : 'Error in getting Rooms'});
} else {
res.json({result : result});
}
});