How to use mongodb aggregate with the following data - node.js

Question

I have a database with collection name "sensors" and it looks like this:
{ "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe3"), "type" : "thermometer", "value" : 23, "createdAt" : ISODate("2019-08-09T07:58:31.698Z"), "updatedAt" : ISODate("2019-08-09T07:58:31.698Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe4"), "type" : "hygrometer", "value" : 74, "createdAt" : ISODate("2019-08-09T07:58:31.739Z"), "updatedAt" : ISODate("2019-08-09T07:58:31.739Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"), "type" : "thermometer", "value" : 25, "createdAt" : ISODate("2019-08-09T07:58:32.551Z"), "updatedAt" : ISODate("2019-08-09T07:58:32.551Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"), "type" : "hygrometer", "value" : 86, "createdAt" : ISODate("2019-08-09T07:58:32.584Z"), "updatedAt" : ISODate("2019-08-09T07:58:32.584Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe7"), "type" : "thermometer", "value" : 20, "createdAt" : ISODate("2019-08-09T07:58:33.554Z"), "updatedAt" : ISODate("2019-08-09T07:58:33.554Z"), "__v" : 0 }
{ "_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"), "type" : "hygrometer", "value" : 84, "createdAt" : ISODate("2019-08-09T07:58:33.587Z"), "updatedAt" : ISODate("2019-08-09T07:58:33.587Z"), "__v" : 0 }
What I want to do is to query on the very last two documents, thermometer and hygrometer then check the value for each of the documents. Then based on the conditions I set using $match tag, I perform any operations I want.
MongoClient.connect('mongodb://localhost', { useNewUrlParser: true }, function (err, client) {
if (err) throw err;
var db = client.db('mongodb');
db.collection('sensors').aggregate(
[
{ $sort: { _id: -1 } },
{ $limit: 1 },
{
$match: {"type": "hygrometer", "value": { "$gt": 60 } }
}
]
).toArray(function(err, item) {
if(err) console.log('error');
if(item.length > 0) console.log('Dehumidifier ON');
else console.log('Dehumidifier OFF');
});
This is the implementation for the very last data only (hygrometer) but how should I make it to check the last two documents then perform a separate operation for thermometer for example "AC ON/OFF"? I was thinking somehow make it check when item.type == "thermometer" perform something but that item.type syntax seems to not work.

Answer 1

Please try this :
Query 1:
db.getCollection('sensors').aggregate(
[
{ $sort: { _id: -1 } }, { $group: { _id: '$type', data: { $push: '$$ROOT' } } },
{ $project: { type: '$_id', _id: 0, lastTwo: { $slice: ["$data", 2] } } },
{ $unwind: '$lastTwo' },
{
$match: { $or: [{ 'type': 'hygrometer' }, { "type": "thermometer", "lastTwo.value": { "$gt": 60 } }] }
}
])
Query 2:
//Check the response below & If you want to group again on type, adding `$group` stage to the above query.
db.getCollection('sensors').aggregate(
[
{ $sort: { _id: -1 } }, { $group: { _id: '$type', data: { $push: '$$ROOT' } } },
{ $project: { type: '$_id', _id: 0, lastTwo: { $slice: ["$data", 2] } } },
{ $unwind: '$lastTwo' },
{
$match: { $or: [{ 'type': 'hygrometer' }, { "type": "thermometer", "lastTwo.value": { "$gt": 60 } }] }
}, { $group: { _id: '$type', data: { $push: '$$ROOT' } } }, { $project: { type: '$_id', _id: 0, data: 1 } }
])
In Output 1 you can simply check whether an object with specific type exists or not and do something in code (Vs) in Output 2 you've to check for type and data array is not empty.
Sample Data :
/* 1 */
{
"_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe3"),
"type" : "thermometer",
"value" : 23,
"createdAt" : ISODate("2019-08-09T07:58:31.698Z"),
"updatedAt" : ISODate("2019-08-09T07:58:31.698Z"),
"__v" : 0
}
/* 2 */
{
"_id" : ObjectId("5d4d27a7e1f2cf1d7cba1fe4"),
"type" : "hygrometer",
"value" : 74,
"createdAt" : ISODate("2019-08-09T07:58:31.739Z"),
"updatedAt" : ISODate("2019-08-09T07:58:31.739Z"),
"__v" : 0
}
/* 3 */
{
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
"type" : "thermometer",
"value" : 251,
"createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
"__v" : 0
}
/* 4 */
{
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
"type" : "hygrometer",
"value" : 86,
"createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
"__v" : 0
}
/* 5 */
{
"_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe7"),
"type" : "thermometer",
"value" : 20,
"createdAt" : ISODate("2019-08-09T07:58:33.554Z"),
"updatedAt" : ISODate("2019-08-09T07:58:33.554Z"),
"__v" : 0
}
/* 6 */
{
"_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
"type" : "hygrometer",
"value" : 84,
"createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
"updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
"__v" : 0
}
Output 1:
/* 1 */
{
"type" : "thermometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
"type" : "thermometer",
"value" : 251,
"createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
"__v" : 0
}
}
/* 2 */
{
"type" : "hygrometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
"type" : "hygrometer",
"value" : 84,
"createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
"updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
"__v" : 0
}
}
/* 3 */
{
"type" : "hygrometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
"type" : "hygrometer",
"value" : 86,
"createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
"__v" : 0
}
}
Output 2:
/* 1 */
{
"type" : "hygrometer",
"data" : [
{
"type" : "hygrometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a9e1f2cf1d7cba1fe8"),
"type" : "hygrometer",
"value" : 84,
"createdAt" : ISODate("2019-08-09T07:58:33.587Z"),
"updatedAt" : ISODate("2019-08-09T07:58:33.587Z"),
"__v" : 0
}
},
{
"type" : "hygrometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe6"),
"type" : "hygrometer",
"value" : 86,
"createdAt" : ISODate("2019-08-09T07:58:32.584Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.584Z"),
"__v" : 0
}
}
]
}
/* 2 */
{
"type" : "thermometer",
"data" : [
{
"type" : "thermometer",
"lastTwo" : {
"_id" : ObjectId("5d4d27a8e1f2cf1d7cba1fe5"),
"type" : "thermometer",
"value" : 251,
"createdAt" : ISODate("2019-08-09T07:58:32.551Z"),
"updatedAt" : ISODate("2019-08-09T07:58:32.551Z"),
"__v" : 0
}
}
]
}
Updates as per comments (In case if you need documents irrespective of type, as documents is always ordered), Please try this:
db.sensors.aggregate( [ { $sort: { _id: -1 } }, { $limit: 2 }, { $match: { $or: [{ 'type': 'hygrometer' , "value": { "$gt": 60 }}, { "type": "thermometer", "value": { "$gt": 20 } }] } } ] )
or make $slice: ["$data", 2] to $slice: ["$data", 1] from above query.

Answer 2

After the sort, limit it to 2 and then use $or:
db.aggtest.aggregate([
{ $sort: { _id: -1 } },
{ $limit: 2 },
{$match: { $or: [ {"type": "hygrometer", "value": { "$gt": 60 }}, {"type": "thermometer"} ]}}
])