Filtering object properties from arrays in Angular HTML can be achieved using various methods such as

Question

Filtering object properties from arrays in Angular HTML can be achieved using various methods such as

I am currently working on a unique "Presentation-Editor" tool where I can see all the presentations that have been created. For this overview, I want to showcase the first slide of each presentation as a preview.

However, there is a challenge because I only have the image URL stored in the "slides" array. The "presentations" array simply contains a list of slide IDs used in the presentation.

To solve this issue and filter out the background image, I attempted the following approach:

<div [ngStyle]="{'background-image': 'url('+(slides | filter : {'_id':'presentation.slides[0].slideid'}).imageurl+')'}">

My goal was to extract the URL by filtering the slides array based on the ID of the first slide in the presentation.

Since I need to show every presentation dynamically with this "preview slide," here's roughly what my HTML structure looks like at the moment:

<div *ngFor="let presentation of presentations">
   // Includes the above div
</div>

It could be a syntax error or just too complex. Any suggestions on how I can address this problem?

angular typescript

Answer 1

Answer №1

To improve your object, I suggest mapping it out in advance and adding a new property called thumbnail.

Chances are your component currently looks something like this:

ngOnInit() {
  this.anyService.getPresentations().pipe(
    /*some kind of unsubscription*/
  ).subscribe(presentations => this.presentations = presentations);

  this.anyService.getSlides().pipe(
    /*some kind of unsubscription*/
  ).subscribe(slides => this.slides = slides);
}

Switch to using rxjs and async pipe for a more sophisticated approach:

ngOnInit() {
  this.presentations$ = this.anyService.getPresentations();
  this.slides$ = this.anyService.getSlides();

  this.extendedPresentations$ = combineLatest([this.presentations$, this.slides$]).pipe(
    // TODO: handle falsy values
    map(([presentations, slides]) => presentations.map(
      presentation => {
        return {
          ...presentation,
          thumbnail: slides.find(slide => slide._id === presentation.slides[0].slideid).imageurl
        }
      }
    )),
  )
}

Update your template accordingly:

<div *ngFor="let presentation of extendedPresentations$ | async">
   <div [ngStyle]="{'background-image': presentation.thumbnail}">
</div>

Answer 2

To improve your object, I suggest mapping it out in advance and adding a new property called thumbnail.

Chances are your component currently looks something like this:

ngOnInit() {
  this.anyService.getPresentations().pipe(
    /*some kind of unsubscription*/
  ).subscribe(presentations => this.presentations = presentations);

  this.anyService.getSlides().pipe(
    /*some kind of unsubscription*/
  ).subscribe(slides => this.slides = slides);
}

Switch to using rxjs and async pipe for a more sophisticated approach:

ngOnInit() {
  this.presentations$ = this.anyService.getPresentations();
  this.slides$ = this.anyService.getSlides();

  this.extendedPresentations$ = combineLatest([this.presentations$, this.slides$]).pipe(
    // TODO: handle falsy values
    map(([presentations, slides]) => presentations.map(
      presentation => {
        return {
          ...presentation,
          thumbnail: slides.find(slide => slide._id === presentation.slides[0].slideid).imageurl
        }
      }
    )),
  )
}

Update your template accordingly:

<div *ngFor="let presentation of extendedPresentations$ | async">
   <div [ngStyle]="{'background-image': presentation.thumbnail}">
</div>

Answer 3

Answer №2

To easily retrieve the URL for a specific slide ID, you can define a function within your TypeScript file:

getSlideUrl(slideId){
  let slide = slides.find(s => s._id == slideId);
  return slide.imageurl;
}

Next, in the user interface (UI) section:

<div *ngFor="let presentation of presentations">
   <div [ngStyle]="{'background-image': 'url('+ getSlideUrl(presentation.slides[0].slideId) +')'}">
</div>

Answer 4

To easily retrieve the URL for a specific slide ID, you can define a function within your TypeScript file:

getSlideUrl(slideId){
  let slide = slides.find(s => s._id == slideId);
  return slide.imageurl;
}

Next, in the user interface (UI) section:

<div *ngFor="let presentation of presentations">
   <div [ngStyle]="{'background-image': 'url('+ getSlideUrl(presentation.slides[0].slideId) +')'}">
</div>

Answer 5

Answer №3

One potential solution to consider involves the following approach:

Within the loop, you can implement the following logic:

<div *ngFor="let presentation of presentations; let i = index;">
  <div [ngStyle]="getBackgroundImage(i)">
</div>

The function responsible for acquiring the background image would resemble this:

getBackgroundImage(i) {
let presentation = presentations[i];
let slide = presentation.slides.filter(
          slide => slide.id === presentation.slides[0].slideId);
}

return {
'background-image': `url($slide.imageurl)`
};

}

Answer 6

One potential solution to consider involves the following approach:

Within the loop, you can implement the following logic:

<div *ngFor="let presentation of presentations; let i = index;">
  <div [ngStyle]="getBackgroundImage(i)">
</div>

The function responsible for acquiring the background image would resemble this:

getBackgroundImage(i) {
let presentation = presentations[i];
let slide = presentation.slides.filter(
          slide => slide.id === presentation.slides[0].slideId);
}

return {
'background-image': `url($slide.imageurl)`
};

}

Filtering object properties from arrays in Angular HTML can be achieved using various methods such as

Answer №1

Answer №2

Answer №3

Similar questions

Sticky header in an Angular Material table

The application is having trouble accessing the property 'isXXXXX' because it is undefined

Is it just me, or does the this.router.subscribe method no longer exist in Angular 2's @angular/router library?

React Native component that enables users to both input their own text and select options from a dropdown menu as they type

What is the best way to locate this particular element on the webpage?

Delay the execution until all promises inside the for loop are resolved in Angular 7 using Typescript

Utilizing the Injector for Quality Testing Services

Is there a way in Angular2 to append a class name from a variable to the host element without removing the current classes?

How can Karma unit tests with Jasmine in a TypeScript Node project accurately measure code coverage, even with external dependencies?

How to set up an Angular ErrorHandler?

Retrieving Data from API in Angular 6/7 upon Navigating Back to Previously Visited Page

Issue: Unable to assign type 'FormDataEntryValue' to type 'string'. Type 'File' cannot be assigned to type 'string'

Tips for troubleshooting errors in rxjs/observable while working with web API in Angular 4

Erasing information and then moving to the identical webpage

Inquiry regarding modules in Javascript/Typescript: export/import and declarations of functions/objects

Real-time monitoring within a callback function in Angular 5

Enabling output hashing for Django and Angular setup

Exploring the traversal of an array of objects within Tree Node

When attempting to retrieve the first element of an array using TypeScript, the browser unfortunately returned an error stating that the property was undefined

Can we use type mapping and conditional types to make it mandatory for an object to have certain specified keys?