What is the necessity of invoking NgZone.run in Angular2 with breezejs for my view to be refreshed?

I've been delving into learning angular2 and recently built a test application with an odata webapi backend. In this app, there's a view that fetches an array of items which I aim to display.

To retrieve data from the frontend, I opted for breezejs library due to its time-saving qualities and compatibility with an odata backend.

This is the structure of my call tree and application:

The process begins with a service function being called from the view to initiate item fetching (noteworthy is that I return an es-6 promise in every call):

this._scrumModuleService.fetchActiveSessions().then((sessions: ScrumSession[]) => {
    // The inclusion of zone.run is necessary for updating the view.
    this._zone.run(() => {
        this.sessions = sessions;
    });
}).catch((error: any) => {
     debugger;
});

Subsequently, the view navigates to the service which then accesses the repository:

public fetchActiveSessions(): Promise<ScrumSession[]> {
    return this._scrumSessionRepository.fetchActiveSessions();
}

The fetch function within the repository:

public fetchActiveSessions(): Promise<ScrumSession[]> {
    return this._dataContext.fetch(new breeze.EntityQuery().from("ScrumSessions").expand(['creator', 'scrumRoom','productOwner', 'users']));
}

Lastly, the repository leads to the (generic) datacontext which executes the query using the breeze entitymanager:

public fetch(query: breeze.EntityQuery, isRetry: boolean = false): Promise<any> {

    return new Promise((resolve, reject) => {
            this.entityManager.executeQuery(query).then((result: breeze.QueryResult): void => {
            // Data has been fetched, so resolve the results
            resolve(result.results);
        });
    });
}

In the view, it's apparent that I have to utilize the run function from NgZone to update automatically as expected in angular2. Despite exploring similar queries without finding a solution, I even implemented the angular2-polyfills script as suggested, yielding no change.

What am I overlooking or what further implementation is required for automatic view updates without calling zone.run?

Answer №1

Current Breeze integration with Angular2 is smooth sailing. We're currently developing a large application using the latest version of Breeze and Angular Beta 8 without any hiccups.

The only minor workaround at the moment is that Breeze doesn't fully utilize the Angular2 http provider yet. However, you can easily work around this by incorporating the default 'Q' provider to support the ES6 Promises required by Angular2. Here's the code snippet:

/**
 * Creating a basic deferred object for Breeze Q/ES6 Promise adapter
 * Ensures compatibility between ES6 promises and Q.
 */
export interface Deferred {
    promise: Promise<any>;
    resolve: (value?: {} | PromiseLike<{}>) => void;
    reject: (reason?: any) => void;
}

/**
 * Basic implementation for Breeze Q/ES6 Promise adapter
 */
export const Q = {
    defer(): Deferred {
        let resolve: (value?: {} | PromiseLike<{}>) => void;
        let reject: (reason?: any) => void;
        let promise = new Promise((_resolve, _reject) => {
            resolve = _resolve;
            reject = _reject;
        })
        return {
            promise: promise,
            resolve(value: any) { resolve(value); },
            reject(reason: any) { reject(reason); }
        }
    },

    resolve(value?: {} | PromiseLike<{}>) {
        let deferred: Deferred = Q['defer']();
        deferred.resolve(value);
        return deferred.promise;
    },


    reject(reason?: any) {
        let deferred: Deferred = Q['defer']();
        deferred.reject(reason);
        return deferred.promise;
    }
}

You can import this file into your project

import { Q } from './q';

then include it near the beginning of your app

breeze.config.setQ(<breeze.promises.IPromiseService>Q);

With this setup, all standard Breeze methods will function as usual, and Angular's change detection should run smoothly.

Answer №2

Angular operates within a zone where the majority of asynchronous APIs are patched. After an async operation is finished, Angular triggers change detection.

The issue arises when Breeze code exits Angular's zone and disrupts change detection. This could be due to initializing Breeze from outside Angular or if Breeze utilizes an asynchronous API that is not patched by Angular's zone, causing callbacks to run outside Angular's zone.

Answer №3

A challenge was encountered due to the use of a promise library (like Q) that zones doesn't recognize. The good news is that Breeze has a plugin for ES6 promises, solving this issue.

Although the Angular 2 http plugin hasn't been created or released yet, it's on our radar as a simple task to tackle. We've just been swamped with other priorities but will get to it soon.

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