How can I select a filtered child document collection when querying a top level document in cosmos db - azure-cosmosdb

Question

I'm trying to filter the child documents returned when querying a parent document using the sql api in cosmos db.
For example given this document:
{
"customerName": "Wallace",
"customerReference": 666777,
"orders": [
{
"date": "20181105T00:00:00",
"amount": 118.84,
"description": "Laptop Battery"
},
{
"date": "20181105T00:00:00",
"amount": 81.27,
"description": "Toner"
},
{
"date": "20181105T00:00:00",
"amount": 55.12,
"description": "Business Cards"
},
{
"date": "20181105T00:00:00",
"amount": 281.00,
"description": "Espresso Machine"
}]
}
I would like to query the customer to retrieve the name, reference and orders over 100.00 to produce a results like this
[{
"customerName": "Wallace",
"customerReference": 666777,
"orders": [
{
"date": "20181105T00:00:00",
"amount": 118.84,
"description": "Laptop Battery"
},
{
"date": "20181105T00:00:00",
"amount": 281.00,
"description": "Espresso Machine"
}]
}]
the query I have so far is as follows
SELECT c.customerName, c.customerReference, c.orders
from c
where c.customerReference = 666777
and c.orders.amount > 100
this returns an empty set
[]
and if you remove "and c.orders.amount > 100" it matches the document and returns all orders.
To reproduce this issue I simply set up a new database, added a new collection and copied the json example in as the only document. The index policy is left as the default which I've copied below.
{
"indexingMode": "consistent",
"automatic": true,
"includedPaths": [
{
"path": "/*",
"indexes": [
{
"kind": "Range",
"dataType": "Number",
"precision": -1
},
{
"kind": "Range",
"dataType": "String",
"precision": -1
},
{
"kind": "Spatial",
"dataType": "Point"
}
]
}
],
"excludedPaths": []
}

Answer 1

Cosmos DB doesn't support the deep filtering in the way I attempted in my original query.
To achieve the results described you need to use a subquery using a combination of ARRAY and VALUE as follows:
SELECT
c.customerName,
c.customerReference,
ARRAY(SELECT Value ord from ord in c.orders WHERE ord.amount > 100) orders
from c
where c.customerReference = 666777
note the use of 'ord' - 'order' is a reserved word.
The query then produces the correct result - eg
[{
"customerName": "Wallace",
"customerReference": 666777,
"orders": [
{
"date": "20181105T00:00:00",
"amount": 118.84,
"description": "Laptop Battery"
},
{
"date": "20181105T00:00:00",
"amount": 281.00,
"description": "Espresso Machine"
}
]
}]