Unable to retrieve JSON data using ng-for

Question

Unable to retrieve JSON data using ng-for

I am dealing with JSON data that contains nested arrays and objects, specifically

Stores[]--->Products[]--->ProductDetails--->ProductTags[]

. Initially, I want to display all the data by writing the following code:

service

export class StoreService {
  //private myurl: string ="apidata/products.json"
  constructor(private _http: Http) {}
  getProducts(): Observable < any > {

    let apiUrl = './assets/products.json';
    return this._http.get(apiUrl)
      .pipe(map((response: Response) => {
        const data = response.json();
        return data;
      }));
  }

store component:

export class StoreComponent implements OnInit {
  products = [];

  constructor(private _storeService: StoreService) {}

  ngOnInit() {
    this._storeService.getProducts()
      .subscribe(data => {
        this.products = data;
        console.log(data)
      });
  }

}

html

<h2>store</h2>
<ul>
  <li *ngFor="let p of products">{{p}}</li>
</ul>

However, when trying to render the data, I encounter the following error:

Error trying to diff '[object Object]'. Only arrays and iterables are allowed

json angular typescript

Answer 1

Answer №1

If you're encountering an error, it could mean that your data is in the form of an object or map rather than an array.

To utilize *ngFor in your template, your data must be structured as an array instead of an object.

An alternative solution introduced by the Angular team is a pipe called "keyvalue" in version 6.1. This allows you to iterate over an object within your Angular template.

Let's say your object resembles the following:

const user = {
    name: 'xyz',
    age: 30,
    gender: 'male'
};

In your template file, you can iterate through this object like so:

<ul>
    <li *ngFor="let data of user | keyvalue">
        Key : {{data.key}} and Value : {{data.value}}
    </li>
</ul>

For more information about this pipe, please visit this link.

Answer 2

If you're encountering an error, it could mean that your data is in the form of an object or map rather than an array.

To utilize *ngFor in your template, your data must be structured as an array instead of an object.

An alternative solution introduced by the Angular team is a pipe called "keyvalue" in version 6.1. This allows you to iterate over an object within your Angular template.

Let's say your object resembles the following:

const user = {
    name: 'xyz',
    age: 30,
    gender: 'male'
};

In your template file, you can iterate through this object like so:

<ul>
    <li *ngFor="let data of user | keyvalue">
        Key : {{data.key}} and Value : {{data.value}}
    </li>
</ul>

For more information about this pipe, please visit this link.

Answer 3

Answer №2

When you encounter this error, it usually means that you are passing an Object instead of an iterable data structure to the *ngFor. The *ngFor directive specifically requires an array for iteration.

To resolve this issue, ensure that when you assign data to this.products, the variable data is actually an array.

UPDATE:

As evident from the console log screenshot:

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

The variable data is found to be an object and not an array. However, properties like PriceFilter, Stores, and GenderFilter on that object contain arrays. To display stores, you can follow this approach:

export class StoreComponent implements OnInit {
  stores = [];

  constructor(private _storeService: StoreService) {}

  ngOnInit() {
    this._storeService.getProducts()
      .subscribe(data => {
        this.stores = data.Stores;
        console.log(data)
      });
  }

}

Update the template as follows:

<h2>Store</h2>
<ul>
  <li *ngFor="let store of stores">
    <h4>Products:</h4>
    <ul>
      <li *ngFor="let product of store.Products">
        <p>Product Id: {{ product.ProductId }}</p>
        <p>Product Title: {{ product.ProductTitle }}</p>
        ...
      </li>
    </ul>
  </li>
</ul>

Answer 4

When you encounter this error, it usually means that you are passing an Object instead of an iterable data structure to the *ngFor. The *ngFor directive specifically requires an array for iteration.

To resolve this issue, ensure that when you assign data to this.products, the variable data is actually an array.

UPDATE:

As evident from the console log screenshot:

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

The variable data is found to be an object and not an array. However, properties like PriceFilter, Stores, and GenderFilter on that object contain arrays. To display stores, you can follow this approach:

export class StoreComponent implements OnInit {
  stores = [];

  constructor(private _storeService: StoreService) {}

  ngOnInit() {
    this._storeService.getProducts()
      .subscribe(data => {
        this.stores = data.Stores;
        console.log(data)
      });
  }

}

Update the template as follows:

<h2>Store</h2>
<ul>
  <li *ngFor="let store of stores">
    <h4>Products:</h4>
    <ul>
      <li *ngFor="let product of store.Products">
        <p>Product Id: {{ product.ProductId }}</p>
        <p>Product Title: {{ product.ProductTitle }}</p>
        ...
      </li>
    </ul>
  </li>
</ul>

Answer 5

Answer №3

If you're encountering this error, it may be due to your data (products) being returned as an object {} instead of an array []. Make sure to check your HTTP Response or make adjustments to your backend API.

For example, you can try assigning this.products = data.Stores; (if you want to iterate over stores).

UPDATE

Based on the link provided in the comments section, you should modify your code like this:

this.products = data.Stores;

Then, update your HTML template:

<div *ngFor="let p of products">
    <ul>
      <li *ngFor="let item of p">
       <-- Extract what you need from your product object here --!>
      </li>
    </ul> 
</div>

Answer 6

If you're encountering this error, it may be due to your data (products) being returned as an object {} instead of an array []. Make sure to check your HTTP Response or make adjustments to your backend API.

For example, you can try assigning this.products = data.Stores; (if you want to iterate over stores).

UPDATE

Based on the link provided in the comments section, you should modify your code like this:

this.products = data.Stores;

Then, update your HTML template:

<div *ngFor="let p of products">
    <ul>
      <li *ngFor="let item of p">
       <-- Extract what you need from your product object here --!>
      </li>
    </ul> 
</div>

Unable to retrieve JSON data using ng-for

Answer №1

Answer №2

UPDATE:

Answer №3

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