5.16.0

changelog.md

@@ -1,5 +1,35 @@
 # Changelog
 
+## 2025-04-25 - 5.16.0 - feat(watcher)
+Enhance change stream watchers with buffering and EventEmitter support; update dependency versions
+
+- Bumped smartmongo from ^2.0.11 to ^2.0.12 and smartrx from ^3.0.7 to ^3.0.10
+- Upgraded @tsclass/tsclass to ^9.0.0 and mongodb to ^6.16.0
+- Refactored the watch API to accept additional options (bufferTimeMs, fullDocument) for improved change stream handling
+- Modified SmartdataDbWatcher to extend EventEmitter and support event notifications
+
+## 2025-04-24 - 5.15.1 - fix(cursor)
+Improve cursor usage documentation and refactor getCursor API to support native cursor modifiers
+
+- Updated examples in readme.md to demonstrate manual iteration using cursor.next() and proper cursor closing.
+- Refactored the getCursor method in classes.doc.ts to accept session and modifier options, consolidating cursor handling.
+- Added new tests in test/test.cursor.ts to verify cursor operations, including limits, sorting, and skipping.
+
+## 2025-04-24 - 5.15.0 - feat(svDb)
+Enhance svDb decorator to support custom serialization and deserialization options
+
+- Added an optional options parameter to the svDb decorator to accept serialize/deserialize functions
+- Updated instance creation logic (updateFromDb) to apply custom deserialization if provided
+- Updated createSavableObject to use custom serialization when available
+
+## 2025-04-23 - 5.14.1 - fix(db operations)
+Update transaction API to consistently pass optional session parameters across database operations
+
+- Revised transaction support in readme to use startSession without await and showcased session usage in getInstance and save calls
+- Updated methods in classes.collection.ts to accept an optional session parameter for findOne, getCursor, findAll, insert, update, delete, and getCount
+- Enhanced SmartDataDbDoc save and delete methods to propagate session parameters
+- Improved overall consistency of transactional APIs across the library
+
 ## 2025-04-23 - 5.14.0 - feat(doc)
 Implement support for beforeSave, afterSave, beforeDelete, and afterDelete lifecycle hooks in document save and delete operations to allow custom logic execution during these critical moments.
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@push.rocks/smartdata",
-  "version": "5.14.0",
+  "version": "5.16.0",
   "private": false,
   "description": "An advanced library for NoSQL data organization and manipulation using TypeScript with support for MongoDB, data validation, collections, and custom data types.",
   "main": "dist_ts/index.js",
@@ -26,23 +26,23 @@
     "@push.rocks/lik": "^6.0.14",
     "@push.rocks/smartdelay": "^3.0.1",
     "@push.rocks/smartlog": "^3.0.2",
-    "@push.rocks/smartmongo": "^2.0.11",
+    "@push.rocks/smartmongo": "^2.0.12",
     "@push.rocks/smartpromise": "^4.0.2",
-    "@push.rocks/smartrx": "^3.0.7",
+    "@push.rocks/smartrx": "^3.0.10",
     "@push.rocks/smartstring": "^4.0.15",
     "@push.rocks/smarttime": "^4.0.6",
     "@push.rocks/smartunique": "^3.0.8",
     "@push.rocks/taskbuffer": "^3.1.7",
-    "@tsclass/tsclass": "^8.2.0",
-    "mongodb": "^6.15.0"
+    "@tsclass/tsclass": "^9.0.0",
+    "mongodb": "^6.16.0"
   },
   "devDependencies": {
     "@git.zone/tsbuild": "^2.3.2",
     "@git.zone/tsrun": "^1.2.44",
     "@git.zone/tstest": "^1.0.77",
     "@push.rocks/qenv": "^6.0.5",
-    "@push.rocks/tapbundle": "^5.6.2",
-    "@types/node": "^22.14.0"
+    "@push.rocks/tapbundle": "^5.6.3",
+    "@types/node": "^22.15.2"
   },
   "files": [
     "ts/**/*",

readme.md

@@ -133,31 +133,34 @@ const user = await User.getInstance({ username: 'myUsername' });
 // Fetch multiple users that match criteria
 const users = await User.getInstances({ email: 'myEmail@example.com' });
 
-// Using a cursor for large collections
+// Obtain a cursor for large result sets
 const cursor = await User.getCursor({ active: true });
 
-// Process documents one at a time (memory efficient)
-await cursor.forEach(async (user, index) => {
-  // Process each user with its position
-  console.log(`Processing user ${index}: ${user.username}`);
+// Stream each document efficiently
+await cursor.forEach(async (user) => {
+  console.log(`Processing user: ${user.username}`);
 });
 
-// Chain cursor methods like in the MongoDB native driver
-const paginatedCursor = await User.getCursor({ active: true })
-  .limit(10) // Limit results
-  .skip(20) // Skip first 20 results
-  .sort({ createdAt: -1 }); // Sort by creation date descending
+// Manually iterate using next()
+let nextUser;
+while ((nextUser = await cursor.next())) {
+  console.log(`Next user: ${nextUser.username}`);
+}
 
-// Convert cursor to array (when you know the result set is small)
-const userArray = await paginatedCursor.toArray();
+// Convert to array when the result set is small
+const userArray = await cursor.toArray();
 
-// Other cursor operations
-const nextUser = await cursor.next(); // Get the next document
-const hasMoreUsers = await cursor.hasNext(); // Check if more documents exist
-const count = await cursor.count(); // Get the count of documents in the cursor
-
-// Always close cursors when done with them
+// Close the cursor to free resources
 await cursor.close();
+
+// For native cursor modifiers (sort, skip, limit), use getCursor with modifier option:
+const paginatedCursor = await User.getCursor(
+  { active: true },
+  { modifier: (c) => c.sort({ createdAt: -1 }).skip(20).limit(10) }
+);
+await paginatedCursor.forEach((user) => {
+  console.log(`Paginated user: ${user.username}`);
+});
 ```
 
 #### Update
@@ -409,19 +412,23 @@ class Product extends SmartDataDbDoc<Product, Product> {
 
 ### Transaction Support
 
-Use MongoDB transactions for atomic operations:
+Use MongoDB transactions for atomic operations. SmartData now exposes `startSession()` and accepts an optional session in all fetch and write APIs:
 
 ```typescript
-const session = await db.startSession();
+// start a client session (no await)
+const session = db.startSession();
 try {
+  // wrap operations in a transaction
   await session.withTransaction(async () => {
-    const user = await User.getInstance({ id: 'user-id' }, { session });
+    // pass session as second arg to getInstance
+    const user = await User.getInstance({ id: 'user-id' }, session);
     user.balance -= 100;
+    // pass session in save opts
     await user.save({ session });
 
-    const recipient = await User.getInstance({ id: 'recipient-id' }, { session });
+    const recipient = await User.getInstance({ id: 'recipient-id' }, session);
     recipient.balance += 100;
-    await user.save({ session });
+    await recipient.save({ session });
   });
 } finally {
   await session.endSession();
@@ -518,6 +525,11 @@ class Order extends SmartDataDbDoc<Order, Order> {
       throw new Error('Order cannot be deleted');
     }
   }
+  // Called after deleting the document
+  async afterDelete() {
+    // Cleanup or audit actions
+    await auditLogDeletion(this.id);
+  }
 }
 ```
 

test/test.cursor.ts

@@ -0,0 +1,97 @@
+import { tap, expect } from '@push.rocks/tapbundle';
+import * as smartmongo from '@push.rocks/smartmongo';
+import { smartunique } from '../ts/plugins.js';
+import * as smartdata from '../ts/index.js';
+
+// Set up database connection
+let smartmongoInstance: smartmongo.SmartMongo;
+let testDb: smartdata.SmartdataDb;
+
+// Define a simple document model for cursor tests
+@smartdata.Collection(() => testDb)
+class CursorTest extends smartdata.SmartDataDbDoc<CursorTest, CursorTest> {
+  @smartdata.unI()
+  public id: string = smartunique.shortId();
+
+  @smartdata.svDb()
+  public name: string;
+
+  @smartdata.svDb()
+  public order: number;
+
+  constructor(name: string, order: number) {
+    super();
+    this.name = name;
+    this.order = order;
+  }
+}
+
+// Initialize the in-memory MongoDB and SmartdataDB
+tap.test('cursor init: start Mongo and SmartdataDb', async () => {
+  smartmongoInstance = await smartmongo.SmartMongo.createAndStart();
+  testDb = new smartdata.SmartdataDb(
+    await smartmongoInstance.getMongoDescriptor(),
+  );
+  await testDb.init();
+});
+
+// Insert sample documents
+tap.test('cursor insert: save 5 test documents', async () => {
+  for (let i = 1; i <= 5; i++) {
+    const doc = new CursorTest(`item${i}`, i);
+    await doc.save();
+  }
+  const count = await CursorTest.getCount({});
+  expect(count).toEqual(5);
+});
+
+// Test that toArray returns all documents
+tap.test('cursor toArray: retrieves all documents', async () => {
+  const cursor = await CursorTest.getCursor({});
+  const all = await cursor.toArray();
+  expect(all.length).toEqual(5);
+});
+
+// Test iteration via forEach
+tap.test('cursor forEach: iterates through all documents', async () => {
+  const names: string[] = [];
+  const cursor = await CursorTest.getCursor({});
+  await cursor.forEach(async (item) => {
+    names.push(item.name);
+  });
+  expect(names.length).toEqual(5);
+  expect(names).toContain('item3');
+});
+
+// Test native cursor modifiers: limit
+tap.test('cursor modifier limit: only two documents', async () => {
+  const cursor = await CursorTest.getCursor({}, { modifier: (c) => c.limit(2) });
+  const limited = await cursor.toArray();
+  expect(limited.length).toEqual(2);
+});
+
+// Test native cursor modifiers: sort and skip
+tap.test('cursor modifier sort & skip: returns correct order', async () => {
+  const cursor = await CursorTest.getCursor({}, {
+    modifier: (c) => c.sort({ order: -1 }).skip(1),
+  });
+  const results = await cursor.toArray();
+  // Skipped the first (order 5), next should be 4,3,2,1
+  expect(results.length).toEqual(4);
+  expect(results[0].order).toEqual(4);
+});
+
+// Cleanup: drop database, close connections, stop Mongo
+tap.test('cursor cleanup: drop DB and stop', async () => {
+  await testDb.mongoDb.dropDatabase();
+  await testDb.close();
+  if (smartmongoInstance) {
+    await smartmongoInstance.stopAndDumpToDir(
+      `.nogit/dbdump/test.cursor.ts`,
+    );
+  }
+  // Ensure process exits after cleanup
+  setTimeout(() => process.exit(), 2000);
+});
+
+export default tap.start();

test/test.watch.ts

@@ -60,6 +60,43 @@ tap.test('should watch a collection', async (toolsArg) => {
   await done.promise;
 });
 
+// ======= New tests for EventEmitter and buffering support =======
+tap.test('should emit change via EventEmitter', async (tools) => {
+  const done = tools.defer();
+  const watcher = await House.watch({});
+  watcher.on('change', async (houseArg) => {
+    // Expect a House instance
+    expect(houseArg).toBeDefined();
+    // Clean up
+    await watcher.stop();
+    done.resolve();
+  });
+  // Trigger an insert to generate a change event
+  const h = new House();
+  await h.save();
+  await done.promise;
+});
+
+tap.test('should buffer change events when bufferTimeMs is set', async (tools) => {
+  const done = tools.defer();
+  // bufferTimeMs collects events into arrays every 50ms
+  const watcher = await House.watch({}, { bufferTimeMs: 50 });
+  let received: House[];
+  watcher.changeSubject.subscribe(async (batch: House[]) => {
+    if (batch && batch.length > 0) {
+      received = batch;
+      await watcher.stop();
+      done.resolve();
+    }
+  });
+  // Rapidly insert multiple docs
+  const docs = [new House(), new House(), new House()];
+  for (const doc of docs) await doc.save();
+  await done.promise;
+  // All inserts should be in one buffered batch
+  expect(received.length).toEqual(docs.length);
+});
+
 // =======================================
 // close the database connection
 // =======================================

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartdata',
-  version: '5.14.0',
+  version: '5.16.0',
   description: 'An advanced library for NoSQL data organization and manipulation using TypeScript with support for MongoDB, data validation, collections, and custom data types.'
 }

ts/classes.collection.ts

@@ -222,53 +222,74 @@ export class SmartdataCollection<T> {
   /**
    * finds an object in the DbCollection
    */
-  public async findOne(filterObject: any): Promise<any> {
+  public async findOne(
+    filterObject: any,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ): Promise<any> {
     await this.init();
-    const cursor = this.mongoDbCollection.find(filterObject);
-    const result = await cursor.next();
-    cursor.close();
-    return result;
+    // Use MongoDB driver's findOne with optional session
+    return this.mongoDbCollection.findOne(filterObject, { session: opts?.session });
   }
 
   public async getCursor(
     filterObjectArg: any,
     dbDocArg: typeof SmartDataDbDoc,
+    opts?: { session?: plugins.mongodb.ClientSession }
   ): Promise<SmartdataDbCursor<any>> {
     await this.init();
-    const cursor = this.mongoDbCollection.find(filterObjectArg);
+    const cursor = this.mongoDbCollection.find(filterObjectArg, { session: opts?.session });
     return new SmartdataDbCursor(cursor, dbDocArg);
   }
 
   /**
    * finds an object in the DbCollection
    */
-  public async findAll(filterObject: any): Promise<any[]> {
+  public async findAll(
+    filterObject: any,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ): Promise<any[]> {
     await this.init();
-    const cursor = this.mongoDbCollection.find(filterObject);
+    const cursor = this.mongoDbCollection.find(filterObject, { session: opts?.session });
     const result = await cursor.toArray();
     cursor.close();
     return result;
   }
 
   /**
-   * watches the collection while applying a filter
+   * Watches the collection, returning a SmartdataDbWatcher with RxJS and EventEmitter support.
+   * @param filterObject match filter for change stream
+   * @param opts optional MongoDB ChangeStreamOptions & { bufferTimeMs } to buffer events
+   * @param smartdataDbDocArg document class for instance creation
    */
   public async watch(
     filterObject: any,
-    smartdataDbDocArg: typeof SmartDataDbDoc,
+    opts: (plugins.mongodb.ChangeStreamOptions & { bufferTimeMs?: number }) = {},
+    smartdataDbDocArg?: typeof SmartDataDbDoc,
   ): Promise<SmartdataDbWatcher> {
     await this.init();
+    // Extract bufferTimeMs from options
+    const { bufferTimeMs, fullDocument, ...otherOptions } = opts || {};
+    // Determine fullDocument behavior: default to 'updateLookup'
+    const changeStreamOptions: plugins.mongodb.ChangeStreamOptions = {
+      ...otherOptions,
+      fullDocument:
+        fullDocument === undefined
+          ? 'updateLookup'
+          : fullDocument === true
+          ? 'updateLookup'
+          : fullDocument,
+    } as any;
+    // Build pipeline with match if provided
+    const pipeline = filterObject ? [{ $match: filterObject }] : [];
     const changeStream = this.mongoDbCollection.watch(
-      [
-        {
-          $match: filterObject,
-        },
-      ],
-      {
-        fullDocument: 'updateLookup',
-      },
+      pipeline,
+      changeStreamOptions,
+    );
+    const smartdataWatcher = new SmartdataDbWatcher(
+      changeStream,
+      smartdataDbDocArg,
+      { bufferTimeMs },
     );
-    const smartdataWatcher = new SmartdataDbWatcher(changeStream, smartdataDbDocArg);
     await smartdataWatcher.readyDeferred.promise;
     return smartdataWatcher;
   }
@@ -276,7 +297,10 @@ export class SmartdataCollection<T> {
   /**
    * create an object in the database
    */
-  public async insert(dbDocArg: T & SmartDataDbDoc<T, unknown>): Promise<any> {
+  public async insert(
+    dbDocArg: T & SmartDataDbDoc<T, unknown>,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ): Promise<any> {
     await this.init();
     await this.checkDoc(dbDocArg);
     this.markUniqueIndexes(dbDocArg.uniqueIndexes);
@@ -287,14 +311,17 @@ export class SmartdataCollection<T> {
     }
     
     const saveableObject = await dbDocArg.createSavableObject();
-    const result = await this.mongoDbCollection.insertOne(saveableObject);
+    const result = await this.mongoDbCollection.insertOne(saveableObject, { session: opts?.session });
     return result;
   }
 
   /**
    * inserts object into the DbCollection
    */
-  public async update(dbDocArg: T & SmartDataDbDoc<T, unknown>): Promise<any> {
+  public async update(
+    dbDocArg: T & SmartDataDbDoc<T, unknown>,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ): Promise<any> {
     await this.init();
     await this.checkDoc(dbDocArg);
     const identifiableObject = await dbDocArg.createIdentifiableObject();
@@ -309,21 +336,27 @@ export class SmartdataCollection<T> {
     const result = await this.mongoDbCollection.updateOne(
       identifiableObject,
       { $set: updateableObject },
-      { upsert: true },
+      { upsert: true, session: opts?.session },
     );
     return result;
   }
 
-  public async delete(dbDocArg: T & SmartDataDbDoc<T, unknown>): Promise<any> {
+  public async delete(
+    dbDocArg: T & SmartDataDbDoc<T, unknown>,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ): Promise<any> {
     await this.init();
     await this.checkDoc(dbDocArg);
     const identifiableObject = await dbDocArg.createIdentifiableObject();
-    await this.mongoDbCollection.deleteOne(identifiableObject);
+    await this.mongoDbCollection.deleteOne(identifiableObject, { session: opts?.session });
   }
 
-  public async getCount(filterObject: any) {
+  public async getCount(
+    filterObject: any,
+    opts?: { session?: plugins.mongodb.ClientSession }
+  ) {
     await this.init();
-    return this.mongoDbCollection.countDocuments(filterObject);
+    return this.mongoDbCollection.countDocuments(filterObject, { session: opts?.session });
   }
 
   /**

ts/classes.db.ts

@@ -63,6 +63,12 @@ export class SmartdataDb {
     this.status = 'disconnected';
     logger.log('info', `disconnected from database ${this.smartdataOptions.mongoDbName}`);
   }
+  /**
+   * Start a MongoDB client session for transactions
+   */
+  public startSession(): plugins.mongodb.ClientSession {
+    return this.mongoDbClient.startSession();
+  }
 
   // handle table to class distribution
 

ts/classes.doc.ts

@@ -11,8 +11,18 @@ import { SmartdataLuceneAdapter } from './classes.lucene.adapter.js';
  * - validate: post-fetch validator, return true to keep a doc
  */
 export interface SearchOptions<T> {
+  /**
+   * Additional MongoDB filter to AND‐merge into the query
+   */
   filter?: Record<string, any>;
+  /**
+   * Post‐fetch validator; return true to keep each doc
+   */
   validate?: (doc: T) => Promise<boolean> | boolean;
+  /**
+   * Optional MongoDB session for transactional operations
+   */
+  session?: plugins.mongodb.ClientSession;
 }
 
 export type TDocCreation = 'db' | 'new' | 'mixed';
@@ -29,16 +39,34 @@ export function globalSvDb() {
   };
 }
 
+/**
+ * Options for custom serialization/deserialization of a field.
+ */
+export interface SvDbOptions {
+  /** Function to serialize the field value before saving to DB */
+  serialize?: (value: any) => any;
+  /** Function to deserialize the field value after reading from DB */
+  deserialize?: (value: any) => any;
+}
+
 /**
  * saveable - saveable decorator to be used on class properties
  */
-export function svDb() {
+export function svDb(options?: SvDbOptions) {
   return (target: SmartDataDbDoc<unknown, unknown>, key: string) => {
     console.log(`called svDb() on >${target.constructor.name}.${key}<`);
     if (!target.saveableProperties) {
       target.saveableProperties = [];
     }
     target.saveableProperties.push(key);
+    // attach custom serializer/deserializer options to the class constructor
+    const ctor = target.constructor as any;
+    if (!ctor._svDbOptions) {
+      ctor._svDbOptions = {};
+    }
+    if (options) {
+      ctor._svDbOptions[key] = options;
+    }
   };
 }
 
@@ -179,7 +207,12 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
     const newInstance = new this();
     (newInstance as any).creationStatus = 'db';
     for (const key of Object.keys(mongoDbNativeDocArg)) {
-      newInstance[key] = mongoDbNativeDocArg[key];
+      const rawValue = mongoDbNativeDocArg[key];
+      const optionsMap = (this as any)._svDbOptions || {};
+      const opts = optionsMap[key];
+      newInstance[key] = opts && typeof opts.deserialize === 'function'
+        ? opts.deserialize(rawValue)
+        : rawValue;
     }
     return newInstance;
   }
@@ -193,8 +226,13 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   public static async getInstances<T>(
     this: plugins.tsclass.typeFest.Class<T>,
     filterArg: plugins.tsclass.typeFest.PartialDeep<T>,
+    opts?: { session?: plugins.mongodb.ClientSession }
   ): Promise<T[]> {
-    const foundDocs = await (this as any).collection.findAll(convertFilterForMongoDb(filterArg));
+    // Pass session through to findAll for transactional queries
+    const foundDocs = await (this as any).collection.findAll(
+      convertFilterForMongoDb(filterArg),
+      { session: opts?.session },
+    );
     const returnArray = [];
     for (const foundDoc of foundDocs) {
       const newInstance: T = (this as any).createInstanceFromMongoDbNativeDoc(foundDoc);
@@ -212,8 +250,13 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   public static async getInstance<T>(
     this: plugins.tsclass.typeFest.Class<T>,
     filterArg: plugins.tsclass.typeFest.PartialDeep<T>,
+    opts?: { session?: plugins.mongodb.ClientSession }
   ): Promise<T> {
-    const foundDoc = await (this as any).collection.findOne(convertFilterForMongoDb(filterArg));
+    // Retrieve one document, with optional session for transactions
+    const foundDoc = await (this as any).collection.findOne(
+      convertFilterForMongoDb(filterArg),
+      { session: opts?.session },
+    );
     if (foundDoc) {
       const newInstance: T = (this as any).createInstanceFromMongoDbNativeDoc(foundDoc);
       return newInstance;
@@ -233,33 +276,27 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   }
 
   /**
-   * get cursor
-   * @returns
+   * Get a cursor for streaming results, with optional session and native cursor modifiers.
+   * @param filterArg Partial filter to apply
+   * @param opts Optional session and modifier for the raw MongoDB cursor
    */
   public static async getCursor<T>(
     this: plugins.tsclass.typeFest.Class<T>,
     filterArg: plugins.tsclass.typeFest.PartialDeep<T>,
-  ) {
-    const collection: SmartdataCollection<T> = (this as any).collection;
-    const cursor: SmartdataDbCursor<T> = await collection.getCursor(
-      convertFilterForMongoDb(filterArg),
-      this as any as typeof SmartDataDbDoc,
-    );
-    return cursor;
-  }
-
-  public static async getCursorExtended<T>(
-    this: plugins.tsclass.typeFest.Class<T>,
-    filterArg: plugins.tsclass.typeFest.PartialDeep<T>,
-    modifierFunction = (cursorArg: plugins.mongodb.FindCursor<plugins.mongodb.WithId<plugins.mongodb.BSON.Document>>) => cursorArg,
+    opts?: {
+      session?: plugins.mongodb.ClientSession;
+      modifier?: (cursorArg: plugins.mongodb.FindCursor<plugins.mongodb.WithId<plugins.mongodb.BSON.Document>>) => plugins.mongodb.FindCursor<plugins.mongodb.WithId<plugins.mongodb.BSON.Document>>;
+    }
   ): Promise<SmartdataDbCursor<T>> {
     const collection: SmartdataCollection<T> = (this as any).collection;
+    const { session, modifier } = opts || {};
     await collection.init();
-    let cursor: plugins.mongodb.FindCursor<any> = collection.mongoDbCollection.find(
-      convertFilterForMongoDb(filterArg),
-    );
-    cursor = modifierFunction(cursor);
-    return new SmartdataDbCursor<T>(cursor, this as any as typeof SmartDataDbDoc);
+    let rawCursor: plugins.mongodb.FindCursor<any> =
+      collection.mongoDbCollection.find(convertFilterForMongoDb(filterArg), { session });
+    if (modifier) {
+      rawCursor = modifier(rawCursor);
+    }
+    return new SmartdataDbCursor<T>(rawCursor, this as any as typeof SmartDataDbDoc);
   }
 
   /**
@@ -268,13 +305,20 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
    * @param filterArg
    * @param forEachFunction
    */
+  /**
+   * Watch the collection for changes, with optional buffering and change stream options.
+   * @param filterArg MongoDB filter to select which changes to observe
+   * @param opts optional ChangeStreamOptions plus bufferTimeMs
+   */
   public static async watch<T>(
     this: plugins.tsclass.typeFest.Class<T>,
     filterArg: plugins.tsclass.typeFest.PartialDeep<T>,
-  ) {
+    opts?: plugins.mongodb.ChangeStreamOptions & { bufferTimeMs?: number },
+  ): Promise<SmartdataDbWatcher<T>> {
     const collection: SmartdataCollection<T> = (this as any).collection;
     const watcher: SmartdataDbWatcher<T> = await collection.watch(
       convertFilterForMongoDb(filterArg),
+      opts || {},
       this as any,
     );
     return watcher;
@@ -339,7 +383,9 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
     if (opts?.filter) {
       mongoFilter = { $and: [mongoFilter, opts.filter] };
     }
-    let docs: T[] = await (this as any).getInstances(mongoFilter);
+    // Fetch with optional session for transactions
+    // Fetch within optional session
+    let docs: T[] = await (this as any).getInstances(mongoFilter, { session: opts?.session });
     if (opts?.validate) {
       const out: T[] = [];
       for (const d of docs) {
@@ -546,10 +592,9 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   constructor() {}
 
   /**
-   * saves this instance but not any connected items
-   * may lead to data inconsistencies, but is faster
+   * saves this instance (optionally within a transaction)
    */
-  public async save() {
+  public async save(opts?: { session?: plugins.mongodb.ClientSession }) {
     // allow hook before saving
     if (typeof (this as any).beforeSave === 'function') {
       await (this as any).beforeSave();
@@ -562,10 +607,10 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
     // perform insert or update
     switch (this.creationStatus) {
       case 'db':
-        dbResult = await this.collection.update(self);
+        dbResult = await this.collection.update(self, { session: opts?.session });
         break;
       case 'new':
-        dbResult = await this.collection.insert(self);
+        dbResult = await this.collection.insert(self, { session: opts?.session });
         this.creationStatus = 'db';
         break;
       default:
@@ -579,15 +624,15 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   }
 
   /**
-   * deletes a document from the database
+   * deletes a document from the database (optionally within a transaction)
    */
-  public async delete() {
+  public async delete(opts?: { session?: plugins.mongodb.ClientSession }) {
     // allow hook before deleting
     if (typeof (this as any).beforeDelete === 'function') {
       await (this as any).beforeDelete();
     }
     // perform deletion
-    const result = await this.collection.delete(this);
+    const result = await this.collection.delete(this, { session: opts?.session });
     // allow hook after delete
     if (typeof (this as any).afterDelete === 'function') {
       await (this as any).afterDelete();
@@ -619,7 +664,12 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   public async updateFromDb() {
     const mongoDbNativeDoc = await this.collection.findOne(await this.createIdentifiableObject());
     for (const key of Object.keys(mongoDbNativeDoc)) {
-      this[key] = mongoDbNativeDoc[key];
+      const rawValue = mongoDbNativeDoc[key];
+      const optionsMap = (this.constructor as any)._svDbOptions || {};
+      const opts = optionsMap[key];
+      this[key] = opts && typeof opts.deserialize === 'function'
+        ? opts.deserialize(rawValue)
+        : rawValue;
     }
   }
 
@@ -629,8 +679,14 @@ export class SmartDataDbDoc<T extends TImplements, TImplements, TManager extends
   public async createSavableObject(): Promise<TImplements> {
     const saveableObject: unknown = {}; // is not exposed to outside, so any is ok here
     const saveableProperties = [...this.globalSaveableProperties, ...this.saveableProperties];
+    // apply custom serialization if configured
+    const optionsMap = (this.constructor as any)._svDbOptions || {};
     for (const propertyNameString of saveableProperties) {
-      saveableObject[propertyNameString] = this[propertyNameString];
+      const rawValue = (this as any)[propertyNameString];
+      const opts = optionsMap[propertyNameString];
+      (saveableObject as any)[propertyNameString] = opts && typeof opts.serialize === 'function'
+        ? opts.serialize(rawValue)
+        : rawValue;
     }
     return saveableObject as TImplements;
   }

ts/classes.watcher.ts

@@ -1,37 +1,73 @@
 import { SmartDataDbDoc } from './classes.doc.js';
 import * as plugins from './plugins.js';
+import { EventEmitter } from 'events';
 
 /**
  * a wrapper for the native mongodb cursor. Exposes better
  */
-export class SmartdataDbWatcher<T = any> {
+/**
+ * Wraps a MongoDB ChangeStream with RxJS and EventEmitter support.
+ */
+export class SmartdataDbWatcher<T = any> extends EventEmitter {
   // STATIC
   public readyDeferred = plugins.smartpromise.defer();
 
   // INSTANCE
   private changeStream: plugins.mongodb.ChangeStream<T>;
-
-  public changeSubject = new plugins.smartrx.rxjs.Subject<T>();
+  private rawSubject: plugins.smartrx.rxjs.Subject<T>;
+  /** Emits change documents (or arrays of documents if buffered) */
+  public changeSubject: any;
+  /**
+   * @param changeStreamArg native MongoDB ChangeStream
+   * @param smartdataDbDocArg document class for instance creation
+   * @param opts.bufferTimeMs optional milliseconds to buffer events via RxJS
+   */
   constructor(
     changeStreamArg: plugins.mongodb.ChangeStream<T>,
     smartdataDbDocArg: typeof SmartDataDbDoc,
+    opts?: { bufferTimeMs?: number },
   ) {
+    super();
+    this.rawSubject = new plugins.smartrx.rxjs.Subject<T>();
+    // Apply buffering if requested
+    if (opts && opts.bufferTimeMs) {
+      this.changeSubject = this.rawSubject.pipe(plugins.smartrx.rxjs.ops.bufferTime(opts.bufferTimeMs));
+    } else {
+      this.changeSubject = this.rawSubject;
+    }
     this.changeStream = changeStreamArg;
     this.changeStream.on('change', async (item: any) => {
-      if (!item.fullDocument) {
-        this.changeSubject.next(null);
-        return;
+      let docInstance: T = null;
+      if (item.fullDocument) {
+        docInstance = smartdataDbDocArg.createInstanceFromMongoDbNativeDoc(
+          item.fullDocument
+        ) as any as T;
       }
-      this.changeSubject.next(
-        smartdataDbDocArg.createInstanceFromMongoDbNativeDoc(item.fullDocument) as any as T,
-      );
+      // Notify subscribers
+      this.rawSubject.next(docInstance);
+      this.emit('change', docInstance);
     });
+    // Signal readiness after one tick
     plugins.smartdelay.delayFor(0).then(() => {
       this.readyDeferred.resolve();
     });
   }
 
-  public async close() {
+  /**
+   * Close the change stream, complete the RxJS subject, and remove listeners.
+   */
+  public async close(): Promise<void> {
+    // Close MongoDB ChangeStream
     await this.changeStream.close();
+    // Complete the subject to teardown any buffering operators
+    this.rawSubject.complete();
+    // Remove all EventEmitter listeners
+    this.removeAllListeners();
+  }
+  /**
+   * Alias for close(), matching README usage
+   */
+  public async stop(): Promise<void> {
+    return this.close();
   }
 }