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Managing File Uploads With NgRx

In this article we will build a fully-functional file upload control, that is powered by Angular and is backed by an NgRx feature store. The control will provide the user with the following features:

  • The ability to upload files using the <input #file type="file" /> HTML element.
  • The ability to see an accurate upload progress via the reportProgress HttpClient option.
  • The ability to cancel in-process uploads

As an added bonus, we will briefly dive into building the server-side ASP.NET Core WebAPI Controller that will handle the file uploads.

Before We Get Started

In this article, I will show you how to manage file uploads using NgRx. If you are new to NgRx, then I highly recommend that you first read my article, NgRx - Best Practices for Enterprise Angular Applications. We will be using the techniques described in that article to build out the NgRx components for file uploads.

If you are new to Angular, then I recommend that you check out one of the following resources:

NPM Package Versions

For context, this article assumes you are using the following npm package.json versions:

  • @angular/*: 7.2.9
  • @ngrx/*: 7.3.0

Prerequisites

Before diving into building the file upload control, make sure that you have the following in place:

  1. An Angular 7+ application generated
  2. NgRx dependencies installed
  3. NgRx Store wired up in your application. e.g. Follow this guide

Create the Upload File Service

Let's create a brand new service in Angular. This service will be responsible for handling the file upload from the client to the server backend. We will use the amazing HttpClient provided with Angular.

Generate the service

$ ng g service file-upload

Inject the HttpClient

Because we are using the HttpClient to make requests to the backend, we need to inject it into our service. Update the constructor line of code so that it looks as follows:

constructor(private httpClient: HttpClient) {}

Add a private field for API_BASE_URL

I typically store API base URLs in the src/environments area. If you're interested in learning more about environments in Angular then check out this great article: Becoming an Angular Environmentalist

Let's create a new private field named API_BASE_URL so that we can use this in our calls to the backend API.

One way to accomplish this would be to do the following:

import { environment } from 'src/environments/environment';
...
private API_BASE_URL = environment.apiBaseUrl;

Add a uploadFile public method

Let's create a new public method named uploadFile to the service. The method will take in a parameter file: File and return an Observable<HttpEvent<{}>>.

Typically a get or post Observable<T> is returned from a service like this. However, in this situation we are going to actually return the raw request which is an Observable<HttpEvent<{}>>.

By returning a raw request we have more control over the process, to pass options like reportProgress and allow cancellation of a request.

public uploadFile(file: File): Observable<HttpEvent<{}>> {
  const formData = new FormData();
  formData.append('files', file, file.name);

  const options = {
    reportProgress: true
  };

  const req = new HttpRequest(
    'POST',
    `${this.API_BASE_URL}/api/file`,
    formData,
    options
  );
  return this.httpClient.request(req);
}

Completed File Upload Service

The completed file-upload.service.ts will look as follows:

import { HttpClient, HttpEvent, HttpRequest } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { environment } from 'src/environments/environment';

@Injectable({
  providedIn: 'root'
})
export class FileUploadService {
  private API_BASE_URL = environment.apiBaseUrl;

  constructor(private httpClient: HttpClient) {}

  public uploadFile(file: File): Observable<HttpEvent<{}>> {
    const formData = new FormData();
    formData.append('files', file, file.name);

    const options = {
      reportProgress: true
    };

    const req = new HttpRequest(
      'POST',
      `${this.API_BASE_URL}/api/file`,
      formData,
      options
    );
    return this.httpClient.request(req);
  }
}

Create the Upload File Feature Store

To keep your NgRx store organized, I recommend creating a separate Upload File Feature Store. Let's bundle it all together in a module named upload-file-store.module.ts and keep it under a sub-directory named upload-file-store.

Create Feature Store Module

Create a feature store module using the following command:

$ ng g module upload-file-store --flat false

Create State Interface

Create a new file underneath the upload-file-store folder, named state.ts. The contents of the file will be as follows:

We are using a relatively new technique in that we will set up an enum to track the status. This enum will reflect the current state of the upload process. For more information on this method, check out Alex Okrushko's article.

export enum UploadStatus {
  Ready = 'Ready',
  Requested = 'Requested',
  Started = 'Started',
  Failed = 'Failed',
  Completed = 'Completed'
}

export interface State {
  status: UploadStatus;
  error: string | null;
  progress: number | null;
}

export const initialState: State = {
  status: UploadStatus.Ready,
  error: null,
  progress: null
};

Create Feature Actions

If you would like to learn more about NgRx Actions, then check out the official docs.

Create a new file underneath the upload-file-store folder, named actions.ts. This file will hold the actions we want to make available on this store.

We will create the following actions on our feature store:

  • UPLOAD_REQUEST - This action is dispatched from the file upload form, it's payload will contain the actual File being uploaded.

  • UPLOAD_CANCEL - This action is dispatched from the file upload form when the cancel button is clicked. This will be used to cancel uploads in progress.

  • UPLOAD_RESET - This action is dispatched from the file upload form when the reset button is clicked. This will be used to reset the state of the store to defaults.

  • UPLOAD_STARTED - This action is dispatched from the file upload effect, HttpClient when the API reports the HttpEventType.Sent event.

  • UPLOAD_PROGRESS - This action is dispatched from the file upload effect, HttpClient when the API reports the HttpEventType.UploadProgress event. The payload will contain the progress percentage as a whole number.

  • UPLOAD_FAILURE - This action is dispatched from the file upload effect when the API returns an error, or there is an HttpEventType.ResponseHeader or HttpEventType.Response with an event.status !== 200, or when an unknown HttpEventType is returned. The payload will contain the specific error message returned from the API and place it into an error field on the store.

  • UPLOAD_COMPLETED - This action is dispatched from the file upload effect when the API reports a HttpEventType.ResponseHeader or HttpEventType.Response event event.status === 200. There is no payload as the API just returns a 200 OK repsonse.

The final actions.ts file will look as follows:

import { Action } from '@ngrx/store';

export enum ActionTypes {
  UPLOAD_REQUEST = '[File Upload Form] Request',
  UPLOAD_CANCEL = '[File Upload Form] Cancel',
  UPLOAD_RESET = '[File Upload Form] Reset',
  UPLOAD_STARTED = '[File Upload API] Started',
  UPLOAD_PROGRESS = '[File Upload API] Progress',
  UPLOAD_FAILURE = '[File Upload API] Failure',
  UPLOAD_COMPLETED = '[File Upload API] Success'
}

export class UploadRequestAction implements Action {
  readonly type = ActionTypes.UPLOAD_REQUEST;
  constructor(public payload: { file: File }) {}
}

export class UploadCancelAction implements Action {
  readonly type = ActionTypes.UPLOAD_CANCEL;
}

export class UploadResetAction implements Action {
  readonly type = ActionTypes.UPLOAD_RESET;
}

export class UploadStartedAction implements Action {
  readonly type = ActionTypes.UPLOAD_STARTED;
}

export class UploadProgressAction implements Action {
  readonly type = ActionTypes.UPLOAD_PROGRESS;
  constructor(public payload: { progress: number }) {}
}

export class UploadFailureAction implements Action {
  readonly type = ActionTypes.UPLOAD_FAILURE;
  constructor(public payload: { error: string }) {}
}

export class UploadCompletedAction implements Action {
  readonly type = ActionTypes.UPLOAD_COMPLETED;
}

export type Actions =
  | UploadRequestAction
  | UploadCancelAction
  | UploadResetAction
  | UploadStartedAction
  | UploadProgressAction
  | UploadFailureAction
  | UploadCompletedAction;

Create the Feature Reducer

If you would like to learn more about NgRx Reducers, then check out the official docs.

Create a new file underneath the upload-file-store folder, named reducer.ts. This file will hold the reducer we create to manage state transitions to the store.

We will handle state transitions as follows for the aforementioned actions:

  • UPLOAD_REQUEST - Reset the state, with the exception of setting state.status to UploadStatus.Requested.

  • UPLOAD_CANCEL - Reset the state tree. Our effect will listen for any UPLOAD_CANCEL event dispatches so a specific state field is not needed for this.

  • UPLOAD_RESET - Reset the state tree on this action.

  • UPLOAD_FAILURE - Reset the state tree, with the exception of setting state.status to UploadStatus.Failed and state.error to the error that was throw in the catchError from the API in the uploadRequestEffect effect.

  • UPLOAD_STARTED - Set state.progress to 0 and state.status to UploadStatus.Started.

  • UPLOAD_PROGRESS - Set state.progress to the current action.payload.progress provided from the action.

  • UPLOAD_COMPLETED - Reset the state tree, with the exception of setting state.status to UploadStatus.Completed so that the UI can display a success message.

import { Actions, ActionTypes } from './actions';
import { initialState, State, UploadStatus } from './state';

export function featureReducer(state = initialState, action: Actions): State {
  switch (action.type) {
    case ActionTypes.UPLOAD_REQUEST: {
      return {
        ...state,
        status: UploadStatus.Requested,
        progress: null,
        error: null
      };
    }
    case ActionTypes.UPLOAD_CANCEL: {
      return {
        ...state,
        status: UploadStatus.Ready,
        progress: null,
        error: null
      };
    }
    case ActionTypes.UPLOAD_RESET: {
      return {
        ...state,
        status: UploadStatus.Ready,
        progress: null,
        error: null
      };
    }
    case ActionTypes.UPLOAD_FAILURE: {
      return {
        ...state,
        status: UploadStatus.Failed,
        error: action.payload.error,
        progress: null
      };
    }
    case ActionTypes.UPLOAD_STARTED: {
      return {
        ...state,
        status: UploadStatus.Started,
        progress: 0
      };
    }
    case ActionTypes.UPLOAD_PROGRESS: {
      return {
        ...state,
        progress: action.payload.progress
      };
    }
    case ActionTypes.UPLOAD_COMPLETED: {
      return {
        ...state,
        status: UploadStatus.Completed,
        progress: 100,
        error: null
      };
    }
    default: {
      return state;
    }
  }
}

Create the Feature Effects

If you would like to learn more about NgRx Effects, then check out the official docs.

Create a new file underneath the upload-file-store folder, named effects.ts. This file will hold the effects that we create to handle any side-effect calls to the backend API service. This effect is where most of the magic happens in the application.

Inject Dependencies

Let's add the necessary dependencies to our constructor as follows:

constructor(
  private fileUploadService: FileUploadService,
  private actions$: Actions<fromFileUploadActions.Actions>
) {}

Add a new Upload Request Effect

Effects make heavy-use of RxJS concepts and topics. If you are new to RxJS then I suggest you check out the official docs

Let's create a new effect in the file named uploadRequestEffect$.

A couple comments about what this effect is going to do:

  • Listen for the UPLOAD_REQUEST action and then make calls to the fileUploadService.uploadFile service method to initiate the upload process.

  • Use the concatMap RxJS operator here so that multiple file upload requests are queued up and processed in the order they were dispatched.

  • Use the takeUntil RxJS operator listening for an UPLOAD_CANCEL action to be dispatched. This allows us to short-circuit any requests that are in-flight.

  • Use the map RxJS operator to map specific HttpEvent responses to dispatch specific Actions that we have defined in our Store.

  • Use the catchError RxJS operator to handle any errors that may be thrown from the HttpClient.

The effect will look something like this:

@Effect()
uploadRequestEffect$: Observable<Action> = this.actions$.pipe(
  ofType(fromFileUploadActions.ActionTypes.UPLOAD_REQUEST),
  concatMap(action =>
    this.fileUploadService.uploadFile(action.payload.file).pipe(
      takeUntil(
        this.actions$.pipe(
          ofType(fromFileUploadActions.ActionTypes.UPLOAD_CANCEL)
        )
      ),
      map(event => this.getActionFromHttpEvent(event)),
      catchError(error => of(this.handleError(error)))
    )
  )
);

Add the getActionFromHttpEvent private method

For more information on listening to progress events, check out the official docs guide from here.

This method will be responsible for mapping a specific HttpEventType to a specific Action that is dispatched.

  • HttpEventType.Sent - This event occurs when the upload process has begun. We will dispatch an UPLOAD_STARTED action to denote that the process has begun.

  • HttpEventType.UploadProgress - This event occurs when the upload process has made progress. We will dispatch an UPLOAD_PROGRESS action with a payload of progress: Math.round((100 * event.loaded) / event.total) to calculate the actual percentage complete of upload. This is because the HttpClient returns an event.loaded and event.total property in whole number format.

  • HttpEventType.Response / HttpEventType.ResponseHeader - These events occur when the upload process has finished. It is important to note that this could be a success or failure so we need to interrogate the event.status to check for 200. We will dispatch the UPLOAD_COMPLETED action if event.status === 200 and UPLOAD_FAILURE if the event.status !== 200 passing the event.statusText as the error payload.

  • All Others (default case) - We treat any other events that may be returned as an error because they are unexpected behavior. We will dispatch a UPLOAD_FAILURE action with a payload of the event run through JSON.stringify.

private getActionFromHttpEvent(event: HttpEvent<any>) {
  switch (event.type) {
    case HttpEventType.Sent: {
      return new fromFileUploadActions.UploadStartedAction();
    }
    case HttpEventType.UploadProgress: {
      return new fromFileUploadActions.UploadProgressAction({
        progress: Math.round((100 * event.loaded) / event.total)
      });
    }
    case HttpEventType.ResponseHeader:
    case HttpEventType.Response: {
      if (event.status === 200) {
        return new fromFileUploadActions.UploadCompletedAction();
      } else {
        return new fromFileUploadActions.UploadFailureAction({
          error: event.statusText
        });
      }
    }
    default: {
      return new fromFileUploadActions.UploadFailureAction({
        error: `Unknown Event: ${JSON.stringify(event)}`
      });
    }
  }
}

Add the handleError private method

For more information on handling HttpClient errors, check out the official docs guide from here.

This method will be responsible for handling any errors that may be thrown from the HttpClient during requests. I am making use of a neat library from npm named serialize-error to give me a predictable error.message no matter what type of error is thrown.

Install the library as so:

$ npm install serialize-error
import serializeError from 'serialize-error';
...
private handleError(error: any) {
  const friendlyErrorMessage = serializeError(error).message;
  return new fromFileUploadActions.UploadFailureAction({
    error: friendlyErrorMessage
  });
}

Completed Feature Effect

The completed effect will look something like this:

import { HttpEvent, HttpEventType } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Actions, Effect, ofType } from '@ngrx/effects';
import { Action } from '@ngrx/store';
import { Observable, of } from 'rxjs';
import { catchError, concatMap, map, takeUntil } from 'rxjs/operators';
import serializeError from 'serialize-error';
import { FileUploadService } from 'src/app/_services';
import * as fromFileUploadActions from './actions';

@Injectable()
export class UploadFileEffects {
  @Effect()
  uploadRequestEffect$: Observable<Action> = this.actions$.pipe(
    ofType(fromFileUploadActions.ActionTypes.UPLOAD_REQUEST),
    concatMap(action =>
      this.fileUploadService.uploadFile(action.payload.file).pipe(
        takeUntil(
          this.actions$.pipe(
            ofType(fromFileUploadActions.ActionTypes.UPLOAD_CANCEL)
          )
        ),
        map(event => this.getActionFromHttpEvent(event)),
        catchError(error => of(this.handleError(error)))
      )
    )
  );

  constructor(
    private fileUploadService: FileUploadService,
    private actions$: Actions<fromFileUploadActions.Actions>
  ) {}

  private getActionFromHttpEvent(event: HttpEvent<any>) {
    switch (event.type) {
      case HttpEventType.Sent: {
        return new fromFileUploadActions.UploadStartedAction();
      }
      case HttpEventType.UploadProgress: {
        return new fromFileUploadActions.UploadProgressAction({
          progress: Math.round((100 * event.loaded) / event.total)
        });
      }
      case HttpEventType.ResponseHeader:
      case HttpEventType.Response: {
        if (event.status === 200) {
          return new fromFileUploadActions.UploadCompletedAction();
        } else {
          return new fromFileUploadActions.UploadFailureAction({
            error: event.statusText
          });
        }
      }
      default: {
        return new fromFileUploadActions.UploadFailureAction({
          error: `Unknown Event: ${JSON.stringify(event)}`
        });
      }
    }
  }

  private handleError(error: any) {
    const friendlyErrorMessage = serializeError(error).message;
    return new fromFileUploadActions.UploadFailureAction({
      error: friendlyErrorMessage
    });
  }
}

Create the Feature Selectors

If you would like to learn more about NgRx Selectors, then check out the official docs.

Create a new file underneath the upload-file-store folder, named selectors.ts. This file will hold the selectors we will use to pull specific pieces of state out of the store. These are technically not required, but strongly encouraged. Selectors improve application performance with the use of the MemoizedSelector wrapper. Selectors also simplify UI logic.

We will create a selector for each significant property of the state. This includes the following properties:

  • state.status - Since this is an enum we will create a selector for each enum choice.
  • state.error
  • state.progress

The completed selectors file will look something like the following:

import {
  createFeatureSelector,
  createSelector,
  MemoizedSelector
} from '@ngrx/store';
import { State, UploadStatus } from './state';

const getError = (state: State): string => state.error;

const getStarted = (state: State): boolean =>
  state.status === UploadStatus.Started;

const getRequested = (state: State): boolean =>
  state.status === UploadStatus.Requested;

const getReady = (state: State): boolean => state.status === UploadStatus.Ready;

const getProgress = (state: State): number => state.progress;

const getInProgress = (state: State): boolean =>
  state.status === UploadStatus.Started && state.progress >= 0;

const getFailed = (state: State): boolean =>
  state.status === UploadStatus.Failed;

const getCompleted = (state: State): boolean =>
  state.status === UploadStatus.Completed;

export const selectUploadFileFeatureState: MemoizedSelector<
  object,
  State
> = createFeatureSelector<State>('uploadFile');

export const selectUploadFileError: MemoizedSelector<
  object,
  string
> = createSelector(
  selectUploadFileFeatureState,
  getError
);

export const selectUploadFileReady: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getReady
);

export const selectUploadFileRequested: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getRequested
);

export const selectUploadFileStarted: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getStarted
);

export const selectUploadFileProgress: MemoizedSelector<
  object,
  number
> = createSelector(
  selectUploadFileFeatureState,
  getProgress
);

export const selectUploadFileInProgress: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getInProgress
);

export const selectUploadFileFailed: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getFailed
);

export const selectUploadFileCompleted: MemoizedSelector<
  object,
  boolean
> = createSelector(
  selectUploadFileFeatureState,
  getCompleted
);

Update the Feature Module

We now need to update the feature module UploadFileStoreModule to wire-up the store.

The completed UploadFileStoreModule should look similar to this:

import { CommonModule } from '@angular/common';
import { NgModule } from '@angular/core';
import { EffectsModule } from '@ngrx/effects';
import { StoreModule } from '@ngrx/store';
import { UploadFileEffects } from './effects';
import { featureReducer } from './reducer';

@NgModule({
  declarations: [],
  imports: [
    CommonModule,
    StoreModule.forFeature('uploadFile', featureReducer),
    EffectsModule.forFeature([UploadFileEffects])
  ]
})
export class UploadFileStoreModule {}

Import this module where needed

Make sure to import this new UploadFileStoreModule where it is needed. In this example, we will import this into the AppModule as we do not have any lazy-loaded features.

Update your AppModule to import Store & Effects

Last, make sure that you update your AppModule to import the StoreModule.forRoot and EffectsModule.forRoot.

An updated AppModule may look as follows:

import { HttpClientModule } from '@angular/common/http';
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { EffectsModule } from '@ngrx/effects';
import { StoreModule } from '@ngrx/store';
import { StoreDevtoolsModule } from '@ngrx/store-devtools';
import { environment } from 'src/environments/environment';
import { AppComponent } from './app.component';
import { UploadFileStoreModule } from './upload-file-store/upload-file-store.module';

@NgModule({
  declarations: [AppComponent],
  imports: [
    BrowserModule,
    HttpClientModule,
    StoreModule.forRoot({}),
    EffectsModule.forRoot([]),
    StoreDevtoolsModule.instrument({
      maxAge: 25, // Retains last 25 states
      logOnly: environment.production // Restrict extension to log-only mode
    }),
    UploadFileStoreModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

Let's Review So Far

  • Up to this point, we have created a new FileUploadService that calls our backend API to upload a File object.

  • We have also created a new UploadFileStore feature store that provides Actions, a Reducer, Effects, and Selectors to manage the file upload process.

  • Last, the store has been imported into our AppModule for use.

Now that we have the foundation laid out for us we can turn our attention to the user interface and wire-up a new component to the UploadFileStore that we created to manage our process.

This will be the fun part!

Create the Upload File Component

Let's start by creating a brand-new Component. This component will consist of the following elements:

  • An input element for the user to interact with to upload a file. The change event will dispatch the UploadFileStoreActions.UploadRequest() action

  • A progress percentage to connected to the UploadFileStoreSelectors.selectUploadFileProgress selector for real-time progress

  • A Cancel UPload button to dispatch the UploadFileStoreActions.UploadCancelRequest() action

  • An Upload Another File button to dispatch the UploadFileStoreActions.UploadResetRequest() action and allow for a new file upload

SIDE NOTE: This would be a good scenario to create a connected container with a dumb component, but for the brevity of this article I will show these combined as one. In the example repository, I will show both scenarios.

Generate the component

Click here for more details on using the powerful Angular CLI

$ ng g component upload-file

For simplicity of this article we will just display the progress percentage, this could easily be adapted to hook into the value property of a progress bar control, like the Angular Material library provides.

Update the component *.ts file

Inject the Store

We need to wire-up our store into this component for use. Let's start by injecting the store into the constructor. The finished constructor should look something like this:

...
constructor(private store$: Store<fromFileUploadState.State>) {}

Wire-up our selectors from state

Let's create six (6) public fields on the component. A good practice is to place $ as a suffix so that you know these are Observable and must be subscribed to in the template.

completed$: Observable<boolean>;
progress$: Observable<number>;
error$: Observable<string>;

isInProgress$: Observable<boolean>;
isReady$: Observable<boolean>;
hasFailed$: Observable<boolean>;

Let's hook these up to the store in our ngOnInit life-cycle hook.

ngOnInit() {
  this.completed$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileCompleted)
  );

  this.progress$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileProgress)
  );

  this.error$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileError)
  );

  this.isInProgress$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileInProgress)
  );

  this.isReady$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileReady)
  );

  this.hasFailed$ = this.store$.pipe(
    select(fromFileUploadSelectors.selectUploadFileFailed)
  );
}

Wire-up our action dispatchers

Let's add uploadFile, resetUpload, and cancelUpload methods to connect our button clicks to dispatch actions in the store.

uploadFile(event: any) {
  const files: FileList = event.target.files;
  const file = files.item(0);

  this.store$.dispatch(
    new fromFileUploadActions.UploadRequestAction({
      file
    })
  );

  // clear the input form
  event.srcElement.value = null;
}

resetUpload() {
  this.store$.dispatch(new UploadFileStoreActions.UploadResetAction());
}

cancelUpload() {
  this.store$.dispatch(new UploadFileStoreActions.UploadCancelAction());
}

Finished Component *.ts file

The finished component *.ts file should look similar to the following:

import { Component, OnInit } from '@angular/core';
import { select, Store } from '@ngrx/store';
import { Observable } from 'rxjs';
import * as fromFileUploadActions from 'src/app/upload-file-store/actions';
import * as fromFileUploadSelectors from 'src/app/upload-file-store/selectors';
import * as fromFileUploadState from 'src/app/upload-file-store/state';

@Component({
  selector: 'app-upload-file',
  templateUrl: './upload-file.component.html',
  styleUrls: ['./upload-file.component.css']
})
export class UploadFileComponent implements OnInit {
  completed$: Observable<boolean>;
  progress$: Observable<number>;
  error$: Observable<string>;
  isInProgress$: Observable<boolean>;
  isReady$: Observable<boolean>;
  hasFailed$: Observable<boolean>;

  constructor(private store$: Store<fromFileUploadState.State>) {}

  ngOnInit() {
    this.completed$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileCompleted)
    );

    this.progress$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileProgress)
    );

    this.error$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileError)
    );

    this.isInProgress$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileInProgress)
    );

    this.isReady$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileReady)
    );

    this.hasFailed$ = this.store$.pipe(
      select(fromFileUploadSelectors.selectUploadFileFailed)
    );
  }

  uploadFile(event: any) {
    const files: FileList = event.target.files;
    const file = files.item(0);

    this.store$.dispatch(
      new fromFileUploadActions.UploadRequestAction({
        file
      })
    );

    // clear the input form
    event.srcElement.value = null;
  }

  resetUpload() {
    this.store$.dispatch(new fromFileUploadActions.UploadResetAction());
  }

  cancelUpload() {
    this.store$.dispatch(new fromFileUploadActions.UploadCancelAction());
  }
}

Update the component *.html template

We are going to add five (5) major parts to our upload file component.

Add the input field

There is no upload file button, rather we will make use of the built-in input component and hook to the change event. Any time a file is added to the form this event will fire. We also only want to display this form if we are accepting new files to be uploaded, i.e. it has failed or it is ready. We will use the *ngIf structural directive to help here referencing our isReady$ and hasFailed$ observables.

<div class="message" *ngIf="(isReady$ | async) || (hasFailed$ | async)">
  <input #file type="file" multiple (change)="uploadFile($event)" />
</div>

Add the progress message

This message will be displayed when the progress is greater than or equal to 0% and the UploadStatus is Failed. We will use *ngIf to only display if it's in this state using the isInProgress$ selector value. We will set the text of the progress message to the progress$ selector value.

<div class="message" *ngIf="(isInProgress$ | async)">
  <div style="margin-bottom: 14px;">Uploading... {{ progress$ | async }}%</div>
</div>

Add the Cancel Upload button

This button will utilize the *ngIf to only display if the upload is in progress using the isInProgress$ selector value. The click event will trigger the dispatch of the UploadCancelAction.

<div class="message" *ngIf="(isInProgress$ | async)">
  <button (click)="cancelUpload()">Cancel Upload</button>
</div>

Add the Reset Upload button

This button will utilize the *ngIf to only display if the upload is complete using the completed$ selector value. The click event will trigger the dispatch of the UploadResetAction.

<div class="message" *ngIf="(completed$ | async)">
  <h4>
    File has been uploaded successfully!
  </h4>
  <button (click)="resetUpload()">Upload Another File</button>
</div>

Add the Error message

This button will utilize the *ngIf to only display if hasFailed$ selector value returns true. The actual error message is pulled from the error$ selector value.

<div class="message error" *ngIf="(hasFailed$ | async)">
  Error: {{ error$ | async }}
</div>

Finished Component *.html file

<div class="message" *ngIf="(isReady$ | async) || (hasFailed$ | async)">
  <input #file type="file" multiple (change)="uploadFile($event)" />
</div>

<div class="message" *ngIf="(isInProgress$ | async)">
  <div style="margin-bottom: 14px;">Uploading... {{ progress$ | async }}%</div>
</div>

<div class="message" *ngIf="(isInProgress$ | async)">
  <button (click)="cancelUpload()">Cancel Upload</button>
</div>

<div class="message" *ngIf="(completed$ | async)">
  <h4>
    File has been uploaded successfully!
  </h4>
  <button (click)="resetUpload()">Upload Another File</button>
</div>

<div class="message error" *ngIf="(hasFailed$ | async)">
  Error: {{ error$ | async }}
</div>

Add some styles to our Component *.css file

For formatting let's add a few simple classes to our component stylesheet:

.message {
  margin-bottom: 15px;
}

.error {
  color: red;
}

Add the Component to our AppComponent

For the purposes of this article we will add our new UploadFileComponent component to our AppComponent. The template will look as follows:

<app-upload-file></app-upload-file>

(Bonus Feature) Back-end REST Endpoint

For a full mock back-end server checkout my [repository here:

For those of you brave souls that have made it this far... You might be asking what the backend API endpoint looks like. Well, here's an example ASP.NET Core Controller offered free of charge ;-)

public class FileController : ControllerBase
{
    [HttpPost("")]
    public async Task<IActionResult> Post(List<IFormFile> files)
    {
        try
        {
            foreach (var file in files)
            {
                Console.WriteLine($"Begin Uploaded File: {file.FileName}");

                //simulate upload
                Task.Delay(5000).Wait();

                Console.WriteLine($"Finished Uploaded File: {file.FileName}");
            }

            return Ok();
        }
        catch (Exception ex)
        {
            return BadRequest($"Unable to upload file(s).");
        }
    }
}

GitHub Example Repository

I always like to provide working code examples that follow the article. You can find this articles companion application at the following repository:

Conclusion

It's important to remember that I have implemented these best practices in several "real world" applications. While I have found these best practices helpful, and maintainable, I do not believe they are an end-all-be-all solution to your NgRx projects; it's just what has worked for me. I am curious as to what you all think? Please feel free to offer any suggestions, tips, or best practices you've learned when building enterprise Angular applications with NgRx and I will update the article to reflect as such. Happy Coding!