// High cardinality, even distribution, used in queries

// E-commerce: userId for user data
{ "id": "order-123", "userId": "user-456", ... }  // PK: /userId

// Multi-tenant: tenantId
{ "id": "doc-1", "tenantId": "tenant-abc", ... }  // PK: /tenantId

// IoT: deviceId for telemetry
{ "id": "reading-1", "deviceId": "device-789", ... }  // PK: /deviceId

// Logs: synthetic key (date + category)
{ "id": "log-1", "partitionKey": "2024-01-15_errors", ... }  // PK: /partitionKey

// For multi-level distribution (e.g., tenant → user)
// Container created with: /tenantId, /userId

{
  "id": "order-123",
  "tenantId": "acme-corp",
  "userId": "user-456",
  "items": [...]
}

// Query within tenant and user efficiently

// Avoid:
// - Low cardinality (status, type, boolean)
// - Monotonically increasing (timestamp, auto-increment)
// - Frequently updated fields
// - Fields not used in queries

// Bad: Only 3 values → hot partitions
{ "status": "pending" | "completed" | "cancelled" }

// Bad: All writes go to latest partition
{ "timestamp": "2024-01-15T10:30:00Z" }

npm install @azure/cosmos

// lib/cosmosdb.ts
import { CosmosClient, Database, Container } from '@azure/cosmos';

const endpoint = process.env.COSMOS_ENDPOINT!;
const key = process.env.COSMOS_KEY!;
const databaseId = process.env.COSMOS_DATABASE!;

const client = new CosmosClient({ endpoint, key });

// Or with connection string
// const client = new CosmosClient(process.env.COSMOS_CONNECTION_STRING!);

export const database: Database = client.database(databaseId);

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

// types/cosmos.ts
export interface BaseItem {
  id: string;
  _ts?: number;      // Auto-generated timestamp
  _etag?: string;    // For optimistic concurrency
}

export interface User extends BaseItem {
  userId: string;    // Partition key
  email: string;
  name: string;
  createdAt: string;
  updatedAt: string;
}

export interface Order extends BaseItem {
  userId: string;    // Partition key
  orderId: string;
  items: OrderItem[];
  total: number;
  status: 'pending' | 'paid' | 'shipped' | 'delivered';
  createdAt: string;
}

export interface OrderItem {
  productId: string;
  name: string;
  quantity: number;
  price: number;
}

import { getContainer } from './cosmosdb';
import { User } from './types';

const usersContainer = getContainer('users');

async function createUser(data: Omit<User, 'id' | 'createdAt' | 'updatedAt'>): Promise<User> {
  const now = new Date().toISOString();
  const user: User = {
    id: crypto.randomUUID(),
    ...data,
    createdAt: now,
    updatedAt: now
  };

  const { resource } = await usersContainer.items.create(user);
  return resource as User;
}

// Most efficient read - requires id AND partition key
async function getUser(userId: string, id: string): Promise<User | null> {
  try {
    const { resource } = await usersContainer.item(id, userId).read<User>();
    return resource || null;
  } catch (error: any) {
    if (error.code === 404) return null;
    throw error;
  }
}

// If id equals partition key value
async function getUserById(userId: string): Promise<User | null> {
  try {
    const { resource } = await usersContainer.item(userId, userId).read<User>();
    return resource || null;
  } catch (error: any) {
    if (error.code === 404) return null;
    throw error;
  }
}

// Query within partition (efficient)
async function getUserOrders(userId: string): Promise<Order[]> {
  const ordersContainer = getContainer('orders');

  const { resources } = await ordersContainer.items
    .query<Order>({
      query: 'SELECT * FROM c WHERE c.userId = @userId ORDER BY c.createdAt DESC',
      parameters: [{ name: '@userId', value: userId }]
    })
    .fetchAll();

  return resources;
}

// Cross-partition query (use sparingly)
async function getOrdersByStatus(status: string): Promise<Order[]> {
  const ordersContainer = getContainer('orders');

  const { resources } = await ordersContainer.items
    .query<Order>({
      query: 'SELECT * FROM c WHERE c.status = @status',
      parameters: [{ name: '@status', value: status }]
    })
    .fetchAll();

  return resources;
}

// Paginated query
async function getOrdersPaginated(
  userId: string,
  pageSize: number = 10,
  continuationToken?: string
): Promise<{ items: Order[]; continuationToken?: string }> {
  const ordersContainer = getContainer('orders');

  const queryIterator = ordersContainer.items.query<Order>(
    {
      query: 'SELECT * FROM c WHERE c.userId = @userId ORDER BY c.createdAt DESC',
      parameters: [{ name: '@userId', value: userId }]
    },
    {
      maxItemCount: pageSize,
      continuationToken
    }
  );

  const { resources, continuationToken: nextToken } = await queryIterator.fetchNext();

  return {
    items: resources,
    continuationToken: nextToken
  };
}

// Replace entire item
async function updateUser(userId: string, id: string, updates: Partial<User>): Promise<User> {
  const existing = await getUser(userId, id);
  if (!existing) throw new Error('User not found');

  const updated: User = {
    ...existing,
    ...updates,
    updatedAt: new Date().toISOString()
  };

  const { resource } = await usersContainer.item(id, userId).replace(updated);
  return resource as User;
}

// Partial update (patch operations)
async function patchUser(userId: string, id: string, operations: any[]): Promise<User> {
  const { resource } = await usersContainer.item(id, userId).patch(operations);
  return resource as User;
}

// Usage:
await patchUser('user-123', 'user-123', [
  { op: 'set', path: '/name', value: 'New Name' },
  { op: 'set', path: '/updatedAt', value: new Date().toISOString() },
  { op: 'incr', path: '/loginCount', value: 1 }
]);

async function deleteUser(userId: string, id: string): Promise<void> {
  await usersContainer.item(id, userId).delete();
}

async function updateUserWithETag(
  userId: string,
  id: string,
  updates: Partial<User>,
  etag: string
): Promise<User> {
  const existing = await getUser(userId, id);
  if (!existing) throw new Error('User not found');

  const updated: User = {
    ...existing,
    ...updates,
    updatedAt: new Date().toISOString()
  };

  try {
    const { resource } = await usersContainer.item(id, userId).replace(updated, {
      accessCondition: { type: 'IfMatch', condition: etag }
    });
    return resource as User;
  } catch (error: any) {
    if (error.code === 412) {
      throw new Error('Document was modified by another process');
    }
    throw error;
  }
}

// Override default consistency
const { resource } = await usersContainer.item(id, userId).read<User>({
  consistencyLevel: 'Strong'
});

// For queries
const { resources } = await container.items.query(
  { query: 'SELECT * FROM c' },
  { consistencyLevel: 'BoundedStaleness' }
).fetchAll();

async function createOrderWithItems(userId: string, order: Order, items: any[]): Promise<void> {
  const ordersContainer = getContainer('orders');

  const operations = [
    { operationType: 'Create' as const, resourceBody: order },
    ...items.map(item => ({
      operationType: 'Create' as const,
      resourceBody: { ...item, userId, orderId: order.orderId }
    }))
  ];

  const { result } = await ordersContainer.items.batch(operations, userId);

  // Check if any operation failed
  if (result.some(r => r.statusCode >= 400)) {
    throw new Error('Batch operation failed');
  }
}

// For large-scale imports (not transactional)
async function bulkImportUsers(users: User[]): Promise<void> {
  const operations = users.map(user => ({
    operationType: 'Create' as const,
    resourceBody: user,
    partitionKey: user.userId
  }));

  // Process in chunks
  const chunkSize = 100;
  for (let i = 0; i < operations.length; i += chunkSize) {
    const chunk = operations.slice(i, i + chunkSize);
    await usersContainer.items.bulk(chunk);
  }
}

import { ChangeFeedStartFrom } from '@azure/cosmos';

async function processChangeFeed(): Promise<void> {
  const container = getContainer('orders');

  const changeFeedIterator = container.items.changeFeed({
    changeFeedStartFrom: ChangeFeedStartFrom.Beginning()
  });

  while (changeFeedIterator.hasMoreResults) {
    const { result: items, statusCode } = await changeFeedIterator.fetchNext();

    if (statusCode === 304) {
      // No new changes
      await sleep(1000);
      continue;
    }

    for (const item of items) {
      console.log('Changed item:', item);
      // Process the change...
    }
  }
}

// For production, use Change Feed Processor with lease container

async function startChangeFeedProcessor(): Promise<void> {
  const sourceContainer = getContainer('orders');
  const leaseContainer = getContainer('leases');

  const changeFeedProcessor = sourceContainer.items.changeFeed
    .for(item => {
      // Process each change
      console.log('Processing:', item);
    })
    .withLeaseContainer(leaseContainer)
    .build();

  await changeFeedProcessor.start();
}

pip install azure-cosmos

undefined

user = {
    'id': user_id,
    'userId': user_id,  # Partition key
    'email': email,
    'name': name,
    'createdAt': now,
    'updatedAt': now
}

return users_container.create_item(user)

return list(users_container.query_items(
    query=query,
    parameters=parameters,
    enable_cross_partition_query=True
))

user.update(updates)
user['updatedAt'] = datetime.utcnow().isoformat()

return users_container.replace_item(item=user_id, body=user)

items = users_container.query_items(
    query=query,
    enable_cross_partition_query=True,
    max_item_count=page_size,
    continuation_token=continuation_token
)

page = items.by_page()
results = list(next(page))

return {
    'items': results,
    'continuation_token': page.continuation_token
}

---

{
  "indexingMode": "consistent",
  "automatic": true,
  "includedPaths": [
    { "path": "/userId/?" },
    { "path": "/status/?" },
    { "path": "/createdAt/?" }
  ],
  "excludedPaths": [
    { "path": "/content/*" },
    { "path": "/_etag/?" }
  ],
  "compositeIndexes": [
    [
      { "path": "/userId", "order": "ascending" },
      { "path": "/createdAt", "order": "descending" }
    ]
  ]
}

await database.containers.createIfNotExists({
  id: 'orders',
  partitionKey: { paths: ['/userId'] },
  indexingPolicy: {
    indexingMode: 'consistent',
    includedPaths: [
      { path: '/userId/?' },
      { path: '/status/?' },
      { path: '/createdAt/?' }
    ],
    excludedPaths: [
      { path: '/*' }  // Exclude all by default
    ]
  }
});

// Container level
await database.containers.createIfNotExists({
  id: 'orders',
  partitionKey: { paths: ['/userId'] },
  throughput: 1000  // RU/s
});

// Scale throughput
const container = database.container('orders');
await container.throughput.replace(2000);

await database.containers.createIfNotExists({
  id: 'orders',
  partitionKey: { paths: ['/userId'] },
  maxThroughput: 10000  // Auto-scales 10% to 100%
});

// No throughput configuration needed
// Pay per request (good for dev/test, intermittent workloads)
await database.containers.createIfNotExists({
  id: 'orders',
  partitionKey: { paths: ['/userId'] }
  // No throughput = serverless
});

undefined

---

// Enable TTL on container
await database.containers.createIfNotExists({
  id: 'sessions',
  partitionKey: { paths: ['/userId'] },
  defaultTtl: 3600  // 1 hour
});

// Per-item TTL
const session = {
  id: 'session-123',
  userId: 'user-456',
  ttl: 1800  // Override: 30 minutes
};