Exploring Model Object Properties with ngFor in Angular

Question

Exploring Model Object Properties with ngFor in Angular

Currently, I am developing an Angular application with a Model object that consists of properties of various types. My goal is to loop through these properties in the component and generate form fields for each property. Unfortunately, the implementation is not displaying anything.

Below is my code:

app.component.html:

<app-principal [model]="model" ></app-principal>

app.component.ts:

import { Component } from '@angular/core';
import { Model } from './model/model';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: './app.component.css'
})
export class AppComponent {
  title = 'frontend';

  model = new Model();
}

principal.component.ts:

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-principal',
  templateUrl: './principal.component.html',
  styleUrls: './principal.component.css'
})
export class PrincipalComponent {
  @Input() model: any;

  getModelProperties(): string[] {
    return Object.keys(this.model);
  }
}

principal.component.html:

<li *ngFor="let property of getModelProperties()">
<label for="{{ property }}">{{ property }}:</label>
<input type="text" [id]="property" [name]="property" placeholder="Write Something" [(ngModel)]="model[property]">
</li>

model.ts:

export class Model {
text!: string;
number!: number;
}

angular typescript

Answer 1

Answer №1

To enhance TypeScript models without using optional `?:`, consider utilizing interfaces and initializing properties. Interfaces are only utilized during compile time to ensure that received data adheres to a specific structure. An implementation of an interface and initialization can be done in the following manner:

export interface IModel{
  text: string;
  number: number;
}

export class Model {
  text: string = "";
  number: number = 0;
}

Once the interface is set up, you can verify structural directives in Angular by employing a dummy object.

import { Component, Input } from '@angular/core';
import { Model } from '../principal-component/principal.model';

@Component({
  selector: 'app-root',
  template: '<app-principal [model]="dummy"></app-principal>',
})

export class AppComponent {
  // Generate using a sample object
  dummy: Model = { text: "something", number: 2321 };
}

If everything is working correctly, the output should resemble this:

https://i.sstatic.net/Spqq3.png

For more information, you can visit:

When to Use Interface and Model in TypeScript/Angular

Understanding the Meaning of ?: in TypeScript

Answer 2

To enhance TypeScript models without using optional `?:`, consider utilizing interfaces and initializing properties. Interfaces are only utilized during compile time to ensure that received data adheres to a specific structure. An implementation of an interface and initialization can be done in the following manner:

export interface IModel{
  text: string;
  number: number;
}

export class Model {
  text: string = "";
  number: number = 0;
}

Once the interface is set up, you can verify structural directives in Angular by employing a dummy object.

import { Component, Input } from '@angular/core';
import { Model } from '../principal-component/principal.model';

@Component({
  selector: 'app-root',
  template: '<app-principal [model]="dummy"></app-principal>',
})

export class AppComponent {
  // Generate using a sample object
  dummy: Model = { text: "something", number: 2321 };
}

If everything is working correctly, the output should resemble this:

https://i.sstatic.net/Spqq3.png

For more information, you can visit:

When to Use Interface and Model in TypeScript/Angular

Understanding the Meaning of ?: in TypeScript

Answer 3

Answer №2

Transforming the class into an interface can be done this way:

export interface Model {
  text: string;
  num: number; // avoid using 'number' as variable name to prevent conflicts
}

After initializing the model with some data, like so:

model:Model = {text: 'someText', num: 5};

You should observe the changes in the template. It's crucial to differentiate between models and arrays when passing them into functions for better clarity.

Answer 4

Transforming the class into an interface can be done this way:

export interface Model {
  text: string;
  num: number; // avoid using 'number' as variable name to prevent conflicts
}

After initializing the model with some data, like so:

model:Model = {text: 'someText', num: 5};

You should observe the changes in the template. It's crucial to differentiate between models and arrays when passing them into functions for better clarity.

Answer 5

Answer №3

While @mohsenmadi made a good attempt in their answer, it's worth noting that TypeScript might raise concerns regarding the access of Model properties using strings. To address this issue, I utilized keyof Model to resolve it.

Furthermore, it's generally not recommended to use a function for populating a loop within your template as it can lead to frequent evaluations and the creation of new objects each time. To optimize this, I modified the main class to populate a properties object via ngOnChanges, which is then utilized in the loop. Additionally, implementing a trackBy function can enhance performance.

Here is an updated version that works: https://stackblitz.com/edit/9daxye-54kkty?file=src%2Fapp%2Fapp.component.html

app.component.ts

import { PrincipalComponent } from './principal/principal.component';
import { Model } from './model/model';

@Component({
  selector: 'app-root',
  standalone: true,
  imports: [PrincipalComponent],
  templateUrl: './app.component.html',
})
export class AppComponent {
  protected model: Model = {num: 5, text: 'test'};
}

model.ts

export interface Model {
  text?: string;
  num?: number;
}

principal.component.ts

import { Component, Input, OnChanges } from '@angular/core';
import { NgFor } from '@angular/common';
import { FormsModule } from '@angular/forms';
import { Model } from '../model/model';

@Component({
  selector: 'app-principal',
  standalone: true,
  imports: [FormsModule, NgFor],
  templateUrl: './principal.component.html',
  styleUrls: ['./principal.component.scss']
})
export class PrincipalComponent implements OnChanges {
  @Input() model: Model = {};

  protected properties: (keyof Model)[] = [];

  ngOnChanges(): void {
    this.properties = Object.keys(this.model) as (keyof Model)[];
  }
}

principal.component.html

<li *ngFor="let property of properties">
  <label for="{{ property }}">{{ property }}:</label>
  <input type="text" [id]="property" [name]="property" placeholder="Write Something" [(ngModel)]="model[property]">
</li>

Answer 6

While @mohsenmadi made a good attempt in their answer, it's worth noting that TypeScript might raise concerns regarding the access of Model properties using strings. To address this issue, I utilized keyof Model to resolve it.

Furthermore, it's generally not recommended to use a function for populating a loop within your template as it can lead to frequent evaluations and the creation of new objects each time. To optimize this, I modified the main class to populate a properties object via ngOnChanges, which is then utilized in the loop. Additionally, implementing a trackBy function can enhance performance.

Here is an updated version that works: https://stackblitz.com/edit/9daxye-54kkty?file=src%2Fapp%2Fapp.component.html

app.component.ts

import { PrincipalComponent } from './principal/principal.component';
import { Model } from './model/model';

@Component({
  selector: 'app-root',
  standalone: true,
  imports: [PrincipalComponent],
  templateUrl: './app.component.html',
})
export class AppComponent {
  protected model: Model = {num: 5, text: 'test'};
}

model.ts

export interface Model {
  text?: string;
  num?: number;
}

principal.component.ts

import { Component, Input, OnChanges } from '@angular/core';
import { NgFor } from '@angular/common';
import { FormsModule } from '@angular/forms';
import { Model } from '../model/model';

@Component({
  selector: 'app-principal',
  standalone: true,
  imports: [FormsModule, NgFor],
  templateUrl: './principal.component.html',
  styleUrls: ['./principal.component.scss']
})
export class PrincipalComponent implements OnChanges {
  @Input() model: Model = {};

  protected properties: (keyof Model)[] = [];

  ngOnChanges(): void {
    this.properties = Object.keys(this.model) as (keyof Model)[];
  }
}

principal.component.html

<li *ngFor="let property of properties">
  <label for="{{ property }}">{{ property }}:</label>
  <input type="text" [id]="property" [name]="property" placeholder="Write Something" [(ngModel)]="model[property]">
</li>

Answer 7

Answer №4

An issue arises with Object.keys not returning the "properties" of a class unless they have a value assigned. (Remember that TypeScript always transpiles to JavaScript) Therefore, you must define your class like this:

// assigning default values
export class Model {
  text: string='';
  number: number=0;
}

Alternatively, you can use a constructor with default values:

// using a constructor with default values
export class Model {
  text!: string;
  number!: number;
  constructor(text:string='',number:number=0){
         this.text=text;
         this.number=number;
  }
}

Another approach is to pass an object with the properties.

By the way, in general, it's not recommended to use a function for looping; it's better to use a getter for your input:

model:any
keys:string[]=[];
@Input('model') set _model(value:any)
{
   this.model=value;
   this.keys=Object.keys(value);
}

Then iterate over the keys:

<li *ngFor="let property of keys">
    ...
</li>

Answer 8

An issue arises with Object.keys not returning the "properties" of a class unless they have a value assigned. (Remember that TypeScript always transpiles to JavaScript) Therefore, you must define your class like this:

// assigning default values
export class Model {
  text: string='';
  number: number=0;
}

Alternatively, you can use a constructor with default values:

// using a constructor with default values
export class Model {
  text!: string;
  number!: number;
  constructor(text:string='',number:number=0){
         this.text=text;
         this.number=number;
  }
}

Another approach is to pass an object with the properties.

By the way, in general, it's not recommended to use a function for looping; it's better to use a getter for your input:

model:any
keys:string[]=[];
@Input('model') set _model(value:any)
{
   this.model=value;
   this.keys=Object.keys(value);
}

Then iterate over the keys:

<li *ngFor="let property of keys">
    ...
</li>

Exploring Model Object Properties with ngFor in Angular

Answer №1

Answer №2

Answer №3

Answer №4

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