How can I do match after second level unwind in mongodb? - mongodb

Question

I am working on a software that uses MongoDB as a database. I have a collection like this (this is just one document)
{
"_id" : ObjectId("5aef51e0af42ea1b70d0c4dc"),
"EndpointId" : "89799bcc-e86f-4c8a-b340-8b5ed53caf83",
"DateTime" : ISODate("2018-05-06T19:05:04.574Z"),
"Url" : "test",
"Tags" : [
{
"Uid" : "E2:02:00:18:DA:40",
"Type" : 1,
"DateTime" : ISODate("2018-05-06T19:05:04.574Z"),
"Sensors" : [
{
"Type" : 1,
"Value" : NumberDecimal("-98")
},
{
"Type" : 2,
"Value" : NumberDecimal("-65")
}
]
},
{
"Uid" : "12:3B:6A:1A:B7:F9",
"Type" : 1,
"DateTime" : ISODate("2018-05-06T19:05:04.574Z"),
"Sensors" : [
{
"Type" : 1,
"Value" : NumberDecimal("-95")
},
{
"Type" : 2,
"Value" : NumberDecimal("-59")
},
{
"Type" : 3,
"Value" : NumberDecimal("12.939770381907275")
}
]
}
]
}
and I want to run this query on it.
db.myCollection.aggregate([
{ $unwind: "$Tags" },
{
$match: {
$and: [
{
"Tags.DateTime": {
$gte: ISODate("2018-05-06T19:05:02Z"),
$lte: ISODate("2018-05-06T19:05:09Z"),
},
},
{ "Tags.Uid": { $in: ["C1:3D:CA:D4:45:11"] } },
],
},
},
{ $unwind: "$Tags.Sensors" },
{ $match: { "$Tags.Sensors.Type": { $in: [1, 2] } } },
{
$project: {
_id: 0,
EndpointId: "$EndpointId",
TagId: "$Tags.Uid",
Url: "$Url",
TagType: "$Tags.Type",
Date: "$Tags.DateTime",
SensorType: "$Tags.Sensors.Type",
Value: "$Tags.Sensors.Value",
},
},
])
the problem is, the second match (that checks $Tags.Sensors.Type) doesn't work and doesn't affect the result of the query.
How can I solve that?
If this is not the right way, what is the right way to run these conditions?

Answer 1

The $match stage accepts field names without a leading $ sign. You've done that correctly in your first $match stage but in the second one you write $Tags.Sensors.Type. Simply removing the leading $ sign should make your query work.
Mind you, the whole thing can be a bit simplified (and some beautification doesn't hurt, either):
You don't need to use $and in your example since it's assumed by default if you specify more than one criterion in a filter.
The $in that you use for the Tags.Sensors.Type filter can be a simple : kind of equality operator unless you have more than one element in the list of acceptable values.
In the $project stage, instead of (kind of) duplicating identical field names you can use the <field>: 1 syntax unless the order of the fields matters.
So the final query would be something like this.
db.myCollection.aggregate([
{
"$unwind" : "$Tags"
},
{
"$match" : {
"Tags.DateTime" : { "$gte" : ISODate("2018-05-06T19:05:02Z"), "$lte" : ISODate("2018-05-06T19:05:09Z") },
"Tags.Uid" : { "$in" : ["C1:3D:CA:D4:45:11"] }
}
}, {
"$unwind" : "$Tags.Sensors"
}, {
"$match" : {
"Tags.Sensors.Type" : { "$in" : [1,2] }
}
},
{
"$project" : {
"_id" : 0,
"EndpointId" : 1,
"TagId" : "$Tags.Uid",
"Url" : 1,
"TagType" : "$Tags.Type",
"Date" : "$Tags.DateTime",
"SensorType" : "$Tags.Sensors.Type",
"Value" : "$Tags.Sensors.Value"
}
}])