diff --git a/.hgtags b/.hgtags
--- a/.hgtags
+++ b/.hgtags
@@ -51,4 +51,5 @@ 435ce00ba2452d565f1ed3bb884643b4b88b9cde
 98b2c550c676ff6acf16f5bd56ee3804342f80b7 v1.9.0-rc3
 515d1b83ebdfaa93599451175055a94f711c079f v1.9.0-rc4
 894b8239b953c0384cf32cab46cf41dac97ea03b v1.9.0-rc5
+63215d91ae4b711eeb2145b9685240e1afada904 v1.9.0-rc6
 af4f8424e83d56e89a64f39e19514ca10dbd43c6 v1.9.0
diff --git a/djx/src/main/ts/observable.ts b/djx/src/main/ts/observable.ts
--- a/djx/src/main/ts/observable.ts
+++ b/djx/src/main/ts/observable.ts
@@ -70,7 +70,10 @@ export const isSubscribable = <T = unkno
     v !== null && v !== undefined && typeof (v as Subscribable<unknown>).subscribe === "function";
 
 export interface Subscribable<T> {
-    subscribe(consumer: Observer<T>): Unsubscribable;
+    /** Subscribes a consumer to events. If a consumer isn't specified
+     * this method activates the producer to achieve side affects if any.
+     */
+    subscribe(consumer?: Observer<T>): Unsubscribable;
 }
 
 export type AccumulatorFn<T, A> = (acc: A, value: T) => A;
@@ -85,6 +88,13 @@ export interface Observable<T> extends S
      */
     map<T2>(mapper: (value: T) => T2): Observable<T2>;
 
+    /** Injects the specified observer into the each producer to consumer chain.
+     * The method is used to add side effect to the events processing.
+     * 
+     * @param observer The consumer for the events
+     */
+    tap(observer: Observer<T>): Observable<T>;
+
     /** Filters elements of the sequence. The resulting sequence will
      * contain only elements which match the specified predicate.
      * 
@@ -203,7 +213,7 @@ const fuse = <T>(producer: Producer<T>) 
 };
 
 const _observe = <T>(producer: FusedProducer<T>): Observable<T> => ({
-    subscribe: (consumer: Observer<T>) => ({
+    subscribe: (consumer: Observer<T> = {}) => ({
         unsubscribe: producer(sink(consumer)) ?? noop
     }),
 
@@ -214,6 +224,14 @@ const _observe = <T>(producer: FusedProd
         })
     ),
 
+    tap: ({next: tapNext, complete: tapComplete, error: tapError}) => _observe(({next,complete, error}) => 
+        producer({
+            next: tapNext ? (v => (tapNext(v), next(v))) : next,
+            complete: tapComplete ? (() => (tapComplete(), complete())): complete,
+            error: tapError ? (e => (tapError(e), error(e))) : error
+        })
+    ),
+
     filter: (predicate) => _observe(({ next, ...rest }) =>
         producer({
             next: next !== noop ? (v: T) => predicate(v) ? next(v) : void (0) : noop,
diff --git a/djx/src/main/ts/store.ts b/djx/src/main/ts/store.ts
--- a/djx/src/main/ts/store.ts
+++ b/djx/src/main/ts/store.ts
@@ -33,34 +33,61 @@ interface Queryable<T, Q, O> {
 export const isDjObservableResults = <T>(v: object): v is DjObservableResults<T> =>
     v && (typeof (v as { observe?: unknown; }).observe === "function");
 
-export const query = <T, Q, O>(store: Queryable<T, Q, O>, includeUpdates = true) =>
-    (query?: Q, options?: O & { observe?: boolean }) => {
-        return observe<OrderedUpdate<T>>(({ next, complete, error, isClosed }) => {
+export const query = <T, Q, O>(store: Queryable<T, Q, O>, includeUpdates = true) => {
+    const q = queryEx(store, includeUpdates);
+    return (query?: Q, options?: O & { observe?: boolean }) => {
+        const [data, updates] = q(query, options);
+
+        return options?.observe === false ? data : data.cat(updates);
+    };
+};
 
+export const queryEx = <T, Q, O>(store: Queryable<T, Q, O>, includeUpdates = true) =>
+    (query?: Q, options?: O): [data: QueryResults<T>, updates: QueryResults<T>] => {
+
+        const pending: T[] = [];
+
+        let results: PromiseOrValue<T[]> = pending;
+
+        const data = observe<OrderedUpdate<T>>(({ next, complete, error }) => {
             const processResults = (items: T[]) =>
                 items.forEach((item, newIndex) => next({ item, newIndex, prevIndex: -1 }));
 
             try {
-                const results = store.query(query, options);
+                if (results === pending)
+                    results = store.query(query, options);
+
                 if (isPromise(results)) {
-                    results.then(processResults).then(undefined, error);
+                    results.then(processResults).then(complete, error);
+
+                    if (isCancellable(results))
+                        return results.cancel.bind(results);
                 } else {
                     processResults(results);
+                    complete();
                 }
+            } catch (e) {
+                error(e);
+            }
+        });
 
-                if (!isClosed() && (options?.observe !== false) && isDjObservableResults<T>(results)) {
+        const updates = observe<OrderedUpdate<T>>(({ next, complete, error, isClosed }) => {
+            try {
+                if (!isClosed() && isDjObservableResults<T>(results)) {
                     const h = results.observe((item, prevIndex, newIndex) => next({ item, prevIndex, newIndex }), includeUpdates);
                     return () => h.remove();
                 } else {
                     complete();
                 }
-            } catch (err) {
-                error(err);
+            } catch (e) {
+                error(e);
             }
         });
 
+        return [data, updates];
     };
 
+
 interface IndexedStore<T> {
     get(id: string | number): PromiseLike<T> | T | null | undefined;
 }
@@ -76,11 +103,11 @@ interface GetOpts {
     observe?: boolean;
 }
 
-type Change<T> = [item: NonNullable<T>, id: string | number | undefined] |
+export type ItemUpdate<T> = [item: NonNullable<T>, id: string | number | undefined] |
 [item: undefined | null, id: string | number];
 
 const filterItem = (itemId: string | number) =>
-    <T>(source: Observable<Change<T>>) =>
+    <T>(source: Observable<ItemUpdate<T>>) =>
         observe<T>(({ next, complete, error }) => {
             const subscription = source
                 .filter(([, id]) => id === itemId)
@@ -94,8 +121,8 @@ const filterItem = (itemId: string | num
 
 export const get = <T>(store: IndexedStore<T>) => {
     const changes = hasNotifications<T>(store) ?
-        observe<Change<T>>(({ next }) => {
-            const handle = after(store, "notify", (...args: Change<T>) => next(args), true);
+        observe<ItemUpdate<T>>(({ next }) => {
+            const handle = after(store, "notify", (...args: ItemUpdate<T>) => next(args), true);
             return () => handle.remove();
         }) : empty;
 
diff --git a/djx/src/test/ts/observable-store-tests.ts b/djx/src/test/ts/observable-store-tests.ts
--- a/djx/src/test/ts/observable-store-tests.ts
+++ b/djx/src/test/ts/observable-store-tests.ts
@@ -1,6 +1,6 @@
 import Memory = require("dojo/store/Memory");
 import Observerable = require("dojo/store/Observable");
-import { get } from "./store";
+import { get, queryEx } from "./store";
 import tap = require("tap");
 
 interface Person {
@@ -61,5 +61,29 @@ tap.test("store::get(...) tests", async 
         samSubscription.unsubscribe();
     }
 
+    store.put({ id: samId, name: "Sam", age: 29});
+
+    const [data, updates] = queryEx(store)({ age: 29}, { sort: [{attribute: "id"}] });
+
+    const dump: string[] = [];
+
+    const subscription = data
+        .tap({
+            complete: () => dump.push("eof")
+        })
+        .cat(updates)
+        .tap({
+            next: ({item: {id}}) => dump.push(id),
+            complete: () => dump.push("eof")
+        })
+        .subscribe({});
+
+    t.same(dump, ["id:peter", "id:sam", "eof"]);
+
+    store.put({ id: "id:mary", name: "Mary", age: 29});
+
+    t.same(dump, ["id:peter", "id:sam", "eof", "id:mary"]);
+
+    subscription.unsubscribe();
 
 }).catch(() => { });
\ No newline at end of file
diff --git a/djx/src/test/ts/observable-tests.ts b/djx/src/test/ts/observable-tests.ts
--- a/djx/src/test/ts/observable-tests.ts
+++ b/djx/src/test/ts/observable-tests.ts
@@ -147,4 +147,27 @@ tap.test("of(...) tests", async t => {
     t.same(await of(1,2,3).collect(), [1,2,3], ".collect() should return the collected sequence");
     await t.rejects(of(1,2,3).collect(cancelled), ".collect() should support cancellation");
 
-}).catch(() => { });
\ No newline at end of file
+}).catch(() => { });
+
+tap.test(".tap() tests", async t => {
+    const side: number[] = [];
+
+    of(1,2)
+        .tap({next: v => side.push(v), complete: () => side.push(0)})
+        .tap({next: v => side.push(v*v)})
+        .subscribe({});
+
+    t.same(side, [1,1,2,4,0], ".tap() should be called in the order of registration");
+
+    side.length = 0;
+
+    await new Promise<void>(resolve => {
+        of(1,2,delay(1).then(() => 3))
+            .tap({next: v => side.push(v)})
+            .tap({ next: v => v === 1 && resolve()})
+            .subscribe({});
+    });
+
+    t.same(side, [1,2], ".tap() should be processed synchronously");
+
+}).catch(() => {});
\ No newline at end of file