Cosmos DB SDK Connection Patterns

Node.js

const \{ CosmosClient \} = require("@azure/cosmos");

const client = new CosmosClient(process.env.COSMOS_CONNECTION_STRING);
const database = client.database("appdb");
const container = database.container("items");

// Query example
const \{ resources \} = await container.items
  .query("SELECT * FROM c WHERE c.userId = @userId", \{
    parameters: [\{ name: "@userId", value: userId \}]
  \})
  .fetchAll();

Python

from azure.cosmos import CosmosClient
import os

client = CosmosClient.from_connection_string(os.environ["COSMOS_CONNECTION_STRING"])
database = client.get_database_client("appdb")
container = database.get_container_client("items")

# Query example
items = container.query_items(
    query="SELECT * FROM c WHERE c.userId = @userId",
    parameters=[\{"name": "@userId", "value": user_id\}]
)

.NET

using Microsoft.Azure.Cosmos;

var client = new CosmosClient(Environment.GetEnvironmentVariable("COSMOS_CONNECTION_STRING"));
var database = client.GetDatabase("appdb");
var container = database.GetContainer("items");

// Query example
var query = new QueryDefinition("SELECT * FROM c WHERE c.userId = @userId")
    .WithParameter("@userId", userId);
var iterator = container.GetItemQueryIterator<dynamic>(query);

Best Practices

Practice	Reason
Reuse client instances	Connection pooling
Use parameterized queries	SQL injection prevention
Set appropriate timeouts	Handle transient failures
Enable diagnostics in dev	Debug RU consumption