Is reading whole object from DocumentDb faster and more efficient? - azure

Question

I'm trying to understand if it would actually be more efficient to read the entire document from Azure DocumentDb than it is to read a property that may have multiple objects in it?
Let's use this basketball team object as an example:
{
id: 123,
name: "Los Angeles Lakers",
coach: "Byron Scott",
players: [
{ id: 24, name: "Kobe Bryant" },
{ id: 3, name: "Anthony Brown" },
{ id: 4, name: "Ryan Kelly" },
]
}
If I want to get only a list of players, is it more efficient/faster for me to read the entire team document from which I can extract the players OR is it better to send SQL statement and try to read only the players from the document?

Answer 1

Returning only the players will be more efficient on the network, as you're returning less data. And, you should also be able to look at the Request Units burned for your query.
For example, I put your document into one of my collections and ran two queries in the portal (and if you do the same, and look at the bottom of the portal, you'll see the resulting Request Unit cost). I slightly modified your document with unique ID and quotes around everything, so I could load it via the portal:
{
"id": "basketball123",
"name": "Los Angeles Lakers",
"coach": "Byron Scott",
"players": [
{ "id": 24, "name": "Kobe Bryant" },
{ "id": 3, "name": "Anthony Brown" },
{ "id": 4, "name": "Ryan Kelly" }
]
}
I first selected just player data:
SELECT c.players FROM c where c.id="basketball123"
with an RU cost of 2.2:
I then asked for the entire document:
SELECT * FROM c where c.id="basketball123"
with an RU cost of 2.24:
Note: Your document size is very small, so there's really not much difference here. But at least you can see that returning a subset costs less than returning the entire document.