cosmos-db-sdk

name: cosmos-db-sdk description: Azure Cosmos DB for NoSQL SDK patterns for the HackOps platform. Covers container operations, parameterized queries, bulk ops, and error handling with @azure/cosmos v4. Use when building API route handlers that read/write Cosmos DB data. Keywords: Cosmos DB, @azure/cosmos, container, query, upsert, bulk, partition key.

Cosmos DB SDK Patterns

@azure/cosmos v4 patterns for the HackOps platform's NoSQL database.

When to Use This Skill

• Writing API route handlers that query or mutate Cosmos DB documents
• Designing partition keys or modeling document schemas
• Handling transactional batch or bulk operations
• Troubleshooting 429 throttling or query performance

Client Initialization

// src/lib/cosmos.ts
import { CosmosClient, type Database, type Container } from "@azure/cosmos";

const client = new CosmosClient({
  endpoint: process.env.COSMOS_ENDPOINT!,
  key: process.env.COSMOS_KEY!,
});

const database: Database = client.database(process.env.COSMOS_DATABASE!);

export function getContainer(name: string): Container {
  return database.container(name);
}

Key Rules

• Client is a singleton — reuse across requests
• For production, prefer DefaultAzureCredential over key-based auth
• Emulator endpoint: https://localhost:8081 (dev only)

Container Layout

Query Patterns

Parameterized Query (MANDATORY)

const { resources } = await container.items
  .query<Team>({
    query: "SELECT * FROM c WHERE c.hackathonId = @hid AND c.status = @status",
    parameters: [
      { name: "@hid", value: hackathonId },
      { name: "@status", value: "active" },
    ],
  })
  .fetchAll();

Never use string interpolation in queries — always use parameters.

Point Read (Preferred for Single Documents)

const { resource } = await container.item(id, partitionKey).read<Hackathon>();
if (!resource) {
  return NextResponse.json({ error: "Not found", ok: false }, { status: 404 });
}

Point reads cost 1 RU — always prefer over queries when you have the id.

Upsert

const { resource } = await container.items.upsert<Hackathon>(document);

Replace with Optimistic Concurrency

const { resource } = await container.item(id, pk).replace<Hackathon>(updated, {
  accessCondition: { type: "IfMatch", condition: etag },
});

Bulk Operations

const operations = items.map((item) => ({
  operationType: "Create" as const,
  resourceBody: item,
}));

const response = await container.items.bulk(operations);

• Bulk operations auto-partition and retry on 429s
• Max 100 operations per batch recommended

Error Handling

import { ErrorResponse } from "@azure/cosmos";

try {
  await container.items.create(doc);
} catch (error) {
  if (error instanceof ErrorResponse) {
    if (error.code === 409) {
      // Conflict — document already exists
    }
    if (error.code === 429) {
      // Throttled — retry after error.retryAfterInMs
    }
    if (error.code === 404) {
      // Not found
    }
  }
  throw error;
}

Cross-Partition Queries

• Avoid when possible — use partition key filters
• enableCrossPartitionQuery: true is required if no partition key filter
• Cost scales linearly with partition count

Session Consistency

The emulator and production both default to Session consistency. Pass x-ms-session-token header for read-your-writes within a session.

Context7 Dynamic Verification

Agents MUST cross-check this skill's patterns against live documentation at both code generation and review time.

When to Verify

• Before generating code that uses patterns from this skill
• During code review passes (app-review-subagent, app-lint-subagent)

Verification Steps

1. Call resolve-library-id for @azure/cosmos
2. Call query-docs with topic "CosmosClient init database" (5000 tokens)
3. Call query-docs with topic "query items bulk operations" (5000 tokens)
4. Compare returned docs against skill patterns
5. If patterns changed, flag discrepancy before proceeding

What to Cross-Check

• CosmosClient constructor options
• container.items.query() method signature
• container.items.bulk() operation type shape
• ErrorResponse class and error code properties

Fallback

If Context7 is unavailable (network error, rate limit, timeout):

1. Warn the user that live verification was not possible
2. Ask for confirmation before proceeding with the skill's hardcoded patterns
3. Do NOT silently fall back — the user must acknowledge the risk

References

• apps/web/src/lib/cosmos.ts — client singleton
• packages/shared/types/api-contract.ts — document type definitions
• docs/exec-plans/active/hackops-execution.md — container layout notes