1# Cosmos DB SDK Connection Patterns
2 
3## Node.js
4 
5```javascript
6const { CosmosClient } = require("@azure/cosmos");
7 
8const client = new CosmosClient(process.env.COSMOS_CONNECTION_STRING);
9const database = client.database("appdb");
10const container = database.container("items");
11 
12// Query example
13const { resources } = await container.items
14  .query("SELECT * FROM c WHERE c.userId = @userId", {
15    parameters: [{ name: "@userId", value: userId }]
16  })
17  .fetchAll();
18```
19 
20## Python
21 
22```python
23from azure.cosmos import CosmosClient
24import os
25 
26client = CosmosClient.from_connection_string(os.environ["COSMOS_CONNECTION_STRING"])
27database = client.get_database_client("appdb")
28container = database.get_container_client("items")
29 
30# Query example
31items = container.query_items(
32    query="SELECT * FROM c WHERE c.userId = @userId",
33    parameters=[{"name": "@userId", "value": user_id}]
34)
35```
36 
37## .NET
38 
39```csharp
40using Microsoft.Azure.Cosmos;
41 
42var client = new CosmosClient(Environment.GetEnvironmentVariable("COSMOS_CONNECTION_STRING"));
43var database = client.GetDatabase("appdb");
44var container = database.GetContainer("items");
45 
46// Query example
47var query = new QueryDefinition("SELECT * FROM c WHERE c.userId = @userId")
48    .WithParameter("@userId", userId);
49var iterator = container.GetItemQueryIterator<dynamic>(query);
50```
51 
52## Best Practices
53 
54| Practice | Reason |
55|----------|--------|
56| Reuse client instances | Connection pooling |
57| Use parameterized queries | SQL injection prevention |
58| Set appropriate timeouts | Handle transient failures |
59| Enable diagnostics in dev | Debug RU consumption |
60