I just finished implementing data polling using ngrx effects. For those unfamiliar with ngrx, it is a popular library for implementing the Redux pattern in Angular applications.

To implement data polling with ngrx effects, you can create an effect that listens for a specific action, such as a POLL_DATA action. When this action is dispatched, the effect can perform an HTTP request to retrieve the data from a remote server, and then dispatch a new action with the data.

You can use the @Effect decorator to create an effect that listens for specific actions. The @Effect decorator takes an options object as an argument, which allows you to specify the action that the effect should listen for and the effect’s behavior.

For example, you might create an effect that listens for the POLL_DATA action and performs an HTTP request to retrieve the data like this:

@Injectable()
export class PollingEffects {
  pollData$: Observable<Action> = this.actions$.pipe(
    ofType(POLL_DATA),
    switchMap(() =>
      this.http.get('/api/data').pipe(
        map((data) => ({ type: DATA_RECEIVED, payload: data })),
        catchError(() => of({ type: DATA_REQUEST_FAILED }))
      )
    )
  );
}

This effect listens for the POLL_DATA action and then performs an HTTP request using the HttpClient service. If the request is successful, it dispatches a DATA_RECEIVED action with the received data as the payload. If the request fails, it dispatches a DATA_REQUEST_FAILED action.

To ensure that the data is polled at regular intervals, you can use the interval operator from the RxJS library. You can modify the effect above to poll the data every 10 seconds like this:

@Injectable()
export class PollingEffects {
  pollData$: Observable<Action> = this.actions$.pipe(
    ofType(POLL_DATA),
    switchMap(() => interval(10000)),
    switchMap(() =>
      this.http.get('/api/data').pipe(
        map((data) => ({ type: DATA_RECEIVED, payload: data })),
        catchError(() => of({ type: DATA_REQUEST_FAILED }))
      )
    )
  );
}

In this modified version of the effect, the interval operator is used to emit a value every 10 seconds (10000 milliseconds). The effect then uses the switchMap operator to perform an HTTP request every time the interval emits a value.

To stop the data polling, you can simply dispatch a new action that the effect can listen for and respond to.

For example, you might create a STOP_POLLING action that the effect can listen for and use to stop polling the data. You can modify the effect above to stop polling when the STOP_POLLING action is dispatched like this:

@Injectable()
export class PollingEffects {
  pollData$: Observable<Action> = this.actions$.pipe(
    ofType(POLL_DATA),
    switchMap(() =>
      interval(10000).pipe(takeUntil(this.actions$.pipe(ofType(STOP_POLLING))))
    ),
    switchMap(() =>
      this.http.get('/api/data').pipe(
        map((data) => ({ type: DATA_RECEIVED, payload: data })),
        catchError(() => of({ type: DATA_REQUEST_FAILED }))
      )
    )
  );
}

In this modified version of the effect, the takeUntil operator is used to stop the data polling when the STOP_POLLING action is dispatched. The takeUntil operator takes an observable as an argument and completes the source observable (in this case, the interval observable) when the argument observable emits a value.

To use this modified effect, you can dispatch the POLL_DATA action to start polling and the STOP_POLLING action to stop polling.

To create a unit test for the data polling effect using the TestScheduler from the RxJS library, you can use the following steps:

First you have to modify your effect to use asyncScheduler like this:

@Injectable()
export class PollingEffects {
  pollData$: Observable<Action> = this.actions$.pipe(
    ofType(POLL_DATA),
    switchMap(() =>
      interval(10000, asyncScheduler).pipe(
        takeUntil(this.actions$.pipe(ofType(STOP_POLLING)))
      )
    ),
    switchMap(() =>
      this.http.get('/api/data').pipe(
        map((data) => ({ type: DATA_RECEIVED, payload: data })),
        catchError(() => of({ type: DATA_REQUEST_FAILED }))
      )
    )
  );
}

In this modified version of the effect, the interval operator is called with the asyncScheduler as the second argument. This causes the interval to use the asyncScheduler to schedule its emissions.

The asyncScheduler is a scheduler that schedules work asynchronously, using the JavaScript interval function. This can be useful if you want to simulate a delay in the data polling effect, or if you want to ensure that the effect is run outside the Angular zone.

I hope this helps clarify how to use the asyncScheduler with the data polling effect. Next you will add your unit tests file and follow the steps:

1. Import the TestScheduler from the RxJS library. The TestScheduler is used to control the virtual time in the test;
2. Create an instance of the TestScheduler and set up the test actions and expected results. To do this, you will need to define the actions that the effect should listen for and the expected results of the effect.
3. Set up the dependencies for the effect under test. This will typically include any services or dependencies that the effect uses, such as the HttpClient service. You can use mock implementations of these dependencies to control their behavior in the test.
4. Create an instance of the effect under test and pass in the dependencies.
5. Pass TestScheduler instance into the effect that is under test. This will execute the effect with a virtual timer.

Here is an example of a unit test for the data polling effect using the TestScheduler:

@Injectable()
export class PollingEffects {

    pollData$ = createEffect(() => ({ scheduler = asyncScheduler} = {}) =>
    this.actions$.pipe(
      ofType(POLL_DATA),
      switchMap(() => interval(10000, asyncScheduler).pipe(
        takeUntil(this.actions$.pipe(ofType(STOP_POLLING)))
      )),
      switchMap(() => this.http.get('/api/data').pipe(
        map(data => ({ type: DATA_RECEIVED, payload: data })),
        catchError(() => of({ type: DATA_REQUEST_FAILED }))
      ))
    )
  );

}

To use the createEffect function from the ngrx library with the data polling effect, you can modify the effect like this:

The createEffect function takes a function that returns an observable as an argument, and returns an observable of actions. The function that is passed to createEffect should contain the logic for the effect.

In this modified version of the effect, the createEffect function is used to wrap the logic for the effect in a way that is compatible with the ngrx store. The effect listens for the POLL_DATA action and performs an HTTP request to retrieve the data every 10 seconds (10000 milliseconds) using asyncScheduler. If the request is successful, it dispatches a DATA_RECEIVED action with the received data as the payload. If the request fails, it dispatches a DATA_REQUEST_FAILED action.

I hope this helps clarify how to use the createEffect function with the data polling effect.

Using ngrx effects to implement data polling is a straightforward process. Essentially, you can create an effect that listens for a specific action, such as a POLL_DATA action, and performs an HTTP request to retrieve data from a remote server. The effect can then dispatch a new action, such as a DATA_RECEIVED action, with the received data as the payload.

To stop the data polling, you can simply dispatch a new action, such as a STOP_POLLING action, that the effect can listen for and use to stop the data polling process.

Unit testing this effect is a bit tricky but you got it!

Hope all the code examples help you!

Hope you enjoyed this article.

Angular: front-end from start to MVP

by Kate Sky

I am making this post as the first step in documenting my journey of building an Enterprise application for my side project.

The application is in the process of going towards an MVP.

This application is an “Uber for home services.” 

The reason I had started this project: is to provide a value-based service while practicing and teaching others skills I had acquired over the years.

The objective of this post is to establish a timeline of the application going live from its infancy.

Following is the list of topics that we are going to discuss in this article:

1. Application Stack
2. Architectural decisions
   1. Monorepo with Nx
   2. Domain-Driven Design with Angular
   3. State management with NGRX
   4. Logging with LogRocket
   5. Authentication with Auth0
3. Conclusion
4. Links

1. Application Stack

WEB- Angular
API – .Net Core
DB – SQL server

2. Architectural decisions

For web client, I am using Angular framework.

My goal – to be able to scale the development of this application by having the ability to go from one team to many teams building multiple frontend and backend applications all in the same workspace. 

I chose NX, so developers have a holistic dev experience powered by an advanced CLI (with editor plugins), capabilities for controlled code sharing, and consistent code generation.

Monorepos allow huge enterprise applications to be subdivided into small and maintainable libraries. I followed the best practice from the creators of NX and have added a domain-driven design approach to creating the features. One of the features is the search capability for the providers that are displayed. I added a domain ‘Providers’ it contains the feature store for state management and the infrastructure where service is implemented to call the API.

We need to first define criteria for slicing our application into individual parts and we must establish rules for communication between them.

referenced: https://www.angulararchitects.io/aktuelles/sustainable-angular-architectures-1/

I have added NGRX from the very beginning because I would like to have an ability to replay the user’s trip through the application, and I will be adding LogRocket to view that path. NGRX will also help me write clean reactive components with async pipes. Root store has its own module and is at the root of the application.

Stop guessing why bugs happen. LogRocket lets you replay what users do on your site, helping you reproduce bugs and fix issues faster.

https://logrocket.com/

Since we have 2 features now, we can see that NGRX stores for each feature are located near the domain for each feature’s library. There is separate module for each store to be able to import each feature module lazily.

Users have to register, and for authentication, I picked Auth0. Right now, you can see that authentication is on the root store. I have a login and logout actions that are calling the service to execute the correct code. I am using the service I download from the example provided by auth0. It still needs to be cleaned up. 

I added a component for the callback path need for the login of the authentication. There is a CanActivate guard that is used for components that need an authorized user.

3 . Conclusion

In conclusion, we will go through whats next.

I wanted to get the frontend started first and have a clear user experience throughout the application.

I will add the .net Core API to store the data to the database next.

I deployed code to GitHub pages to be able to get user feedback at the very early stages of this application.

4. Links

Code: https://github.com/katesky/saraphan-radio

Dev version: https://katesky.github.io/saraphan-radio/

Domain: http://saraphanradio.com

Angular: NGRX clean architecture with multiple stores

by Kate Sky

Before we go into Part 2 (testing of the multi-feature/store), I want to demonstrate the implementation of lazy loading of modules with multiple stores. So the objective of this article will be to show you how to add feature stores to the Feature module, which are loaded lazily when a route is activated.

Finally, I am going to provide links to the repository to GitHub.

Following is the list of topics that we are going to discuss in this article:

1. Application objective.
2. Application architecture
3. Lazy loading of the feature modules
4. Lazy loading demo
5. Conclusion
6. Links
7. Part 2 ( to be continued)

1. The objective of the application     

In this example, I want to demonstrate an app that will track home buying data. It will have a dashboard with links to a favorite list and a list of visited homes. Users will also be able to click on a link that will take her to a list of all prospective homes. From there, she can go into detail for each home.  

2. Application architecture and folder structure

In this example, we have separated this application in high-level feature modules. By doing so, it allows us to lazy load features along with store modules based on the current route.

3. Lazy loading of the feature modules

“By default, NgModules are eagerly loaded, which means that as soon as the app loads, so do all the NgModules, whether or not they are immediately necessary. For large apps with lots of routes, consider lazy loading—a design pattern that loads NgModules as needed. Lazy loading helps keep initial bundle sizes smaller, which in turn helps decrease load times. ” – From Angule.io

We now can lazy load our feature module by registering it in the routing module:

4. Lazy loading demo

When we have a clean separation of the features into modules, it allows us to register routes to be lazy-loaded.
Let’s see it in action by checking the console:

When app navigates to Homes we see that our feature1 module is fetched and an additional file appears in the console:

5. Conclusion

In this article, I tried to deliver a technical guide on how to organize your application NGRX stores and provide you with examples of how they can be registered alongside with routing modules.

We started with an application description. I went over the architecture and folder structure. We then looked at registering a lazy loaded module. Finally, we looked at the demo.

6. Links

• https://github.com/katesky/ngrx-multy-store-part-1.5
• https://stackblitz.com/edit/ngrx-multy-store-part-15

7. Part 2 (To be continued…)

Where I will show how to test a component that uses a feature store. Some mocking will take place.

I hope this article helps you out with adding NGRX to your application.

Angular: NGRX clean architecture with multiple stores

by Kate Sky

The objective of this article is to provide a technical implementation of the NGRX for an application with a complexity that could benefit from adding feature store(s) in addition to the root store.

Finally, I am going to provide links to my GitHub repository with the example code.

In part 2, I will show how to unit test components that use a feature store and later we will go into the unit testing of the NGRX store itself.

This is the list of topics that we are going to discuss in this article:

1. A high-level use case for state management.
2. Getting started with a root store
3. Adding feature store to the application
4. Organizing your store folders
5. Adding stores to your components
6. Conclusion
7. Links
8. Part 2 ( to be continued)

1. High-level use case for state management.

When a decision has been made to manage the state of your complex application by adding NGRX, it is important to understand that you will not be able to convert the whole application to use the store right from the start.

It will be a gradual process that I will try to provide a technical guide for. In the example, you will see a RootStoreModule and a Store1Module.

The root store is where you will start. This store will be the highest level of user/system actions that can be performed in the application. For example, a dashboard app will have links to other areas, so the root store will load the available links and user access and privileges needed for the app to run. Root store will manage the state of the highest level of the application or lowest since it is a root (pun attended).

The feature store is an abstraction for parts of the application that are feature-based. For example, the user will click on a feature of the application from a dashboard, that allows him to manage orders, sales, employees, etc.  This is where the feature will load or change data using the feature store. It will manage the state of this feature along.

First, you must install NGRX by following the installation steps from https://ngrx.io/guide/store/install

2. Getting started with a root store

Second, you will create a folder where you will hold all files related to the root store.

Inside the folder, you will have files needed for the store: actions, effects, reducers and an index file for exports. One of the necessary imports is CommonModule and reducers and effects.

If you use the CLI’s “ng add @ngrx/store” the structure is flatter. I like to organize it in a more 2D way.

Second, you will add the RootStoreModule to the app.module( CLI will add it for you!)

3. Adding Feature store to the application

When adding a feature store module and adding the imports one major difference from the root is the forFeature method.

Ones all the files are created you can add feature module to the app.module just like the RootStoreModule

4. Organizing your store folders

In this simple example, you can see a separate folder for the feature store on the same level as the root store, but in a real application, I recommend adding a feature store folder on the same level as the feature folder.

5. Adding stores to your components

Since this example uses both stores in the app component, it’s pretty clear how easy it is to use the store and create a truly reactive application using an NGRX store.

In AppComponent you can find root store and feature store usage.

Stores are injected into the constructor and actions are dispatched to load the data:

You can see that the template is using the async pipe to load the data, there are no subscribe events. Observables are assigned the selectors from the store:

6. Conclusion

In this article, I tried to deliver a technical guide on how to organize your application NGRX stores and provide you with examples of how they can be organized.

We started by setting up the root and feature stores and registering them in the app module. We then added the stores to a component and saw how data is displayed on the screen.

7. Links

• https://github.com/katesky/ngrx-multy-store
• https://stackblitz.com/edit/github-ngrx-multy-store
• https://github-ngrx-multy-store.stackblitz.io

8. Part 2 (To be continued…)

Where I will show how to test a component that uses a feature store. Some mocking will take place.

I kept this project as simple as possible, so you can even take the source code and add it to your application as a template. I know I will in the future.

I hope this article helps you out with adding NGRX to your application.