CosmosDB, help flatten and filter by nested array - azure-cosmosdb

Question

I'm trying to flatten and filter my json data that is in a CosmosDB.
The data looks like below and I would like to flatten everything in the array Variables and then filter by specific _id and Timestamp inside of the array:
{
"_id": 21032,
"FirstConnected": {
"$date": 1522835868346
},
"LastUpdated": {
"$date": 1523360279908
},
"Variables": [
{
"_id": 99999,
"Values": [
{
"Timestamp": {
"$date": 1522835868347
},
"Value": 1
}
]
},
{
"_id": 99998,
"Values": [
{
"Timestamp": {
"$date": 1523270312001
},
"Value": 8888
}
]
}
]
}

Answer 1

If you want to flatten data from the Variables array with properties from the root object you can query your collection like this:
SELECT root._id, root.FirstConnected, root.LastUpdated, var.Values
FROM root
JOIN var IN root.Variables
WHERE var._id = 99998
This will result into:
[
{
"_id": 21032,
"FirstConnected": {
"$date": 1522835868346
},
"LastUpdated": {
"$date": 1523360279908
},
"Values": [
{
"Timestamp": {
"$date": 1523270312001
},
"Value": 8888
}
]
}
]
If you want to even flatten the Values array you will need to write something like this:
SELECT root._id, root.FirstConnected, root.LastUpdated,
var.Values[0].Timestamp, var.Values[0]["Value"]
FROM root
JOIN var IN root.Variables
WHERE var._id = 99998
Note that CosmosDB considers "Value" as a reserved keyword and you need to use an escpape syntax. The result for this query is:
[
{
"_id": 21032,
"FirstConnected": {
"$date": 1522835868346
},
"LastUpdated": {
"$date": 1523360279908
},
"Timestamp": "1970-01-01T00:00:00Z",
"Value": 8888
}
]
Check for more details https://learn.microsoft.com/en-us/azure/cosmos-db/sql-api-sql-query#Advanced

Answer 2

If you're only looking for filtering by the nested '_id' property then you could use ARRAY_CONTAINS w/ the partial_match argument set to true. The query would look something like this:
SELECT VALUE c
FROM c
WHERE ARRAY_CONTAINS(c.Variables, {_id: 99998}, true)
If you also want to flatten the array, then you could use JOIN
SELECT VALUE v
FROM v IN c.Variables
WHERE v._id = 99998