1// Azure Cosmos DB — @azure/cosmos SDK v4
2// Partition key design: high-cardinality /userId
3
4import { CosmosClient, PartitionKeyKind } from "@azure/cosmos";
5
6const client = new CosmosClient({
7  endpoint: process.env.COSMOS_ENDPOINT!,
8  key: process.env.COSMOS_KEY!,
9});
10
11const { database } = await client.databases.createIfNotExists({ id: "myapp" });
12const { container } = await database.containers.createIfNotExists({
13  id: "orders",
14  partitionKey: {
15    paths: ["/userId"],                    // HIGH cardinality — millions of distinct values
16    kind: PartitionKeyKind.Hash,
17  },
18  defaultTtl: 7776000,                    // 90-day TTL in seconds — prevents unbounded storage growth
19  indexingPolicy: {
20    automatic: true,
21    indexingMode: "consistent",
22    excludedPaths: [{ path: "/rawPayload/*" }],  // exclude large blobs from index — saves RUs
23  },
24});
25
26// Point read — 1 RU. Fastest possible operation.
27// Requires BOTH the item id AND the partition key value.
28const { resource: order } = await container
29  .item("ord-1234", "user-42")            // (id, partitionKeyValue)
30  .read<Order>();
31
32// Cross-partition query — expensive! Use sparingly.
33// EnableScanInQuery lets it run; cost scales with partition count.
34const { resources: recentOrders } = await container.items
35  .query({
36    query: "SELECT * FROM c WHERE c.status = @status AND c._ts > @cutoff",
37    parameters: [
38      { name: "@status", value: "pending" },
39      { name: "@cutoff", value: Math.floor(Date.now() / 1000) - 3600 },
40    ],
41  })
42  .fetchAll();
43
44// Change Feed — react to inserts/updates in real-time
45const changeFeedIterator = container.items.getChangeFeedIterator({
46  changeFeedStartFrom: "Beginning",
47});
48for await (const { result } of changeFeedIterator) {
49  await processChanges(result);            // drives downstream projections, cache invalidation
50}