Data binding in Angular Drop down list component

27 Sep 202315 minutes to read

The DropDownList loads the data either from local data sources or remote data services using the dataSource property. It supports the data type of array or DataManager.
remote data services using the dataSource property. It supports the data type of array or DataManager.

The DropDownList also supports different kinds of data services such as OData, OData V4, and Web API, and data formats such as XML, JSON, and JSONP with the help of DataManageradaptors.

Fields	Type	Description
text	`string`	Specifies the display text of each list item.
value	`number or string`	Specifies the hidden data value mapped to each list item that should contain a unique value.
groupBy	`string`	Specifies the category under which the list item has to be grouped.
iconCss	`string`	Specifies the icon class of each list item.

When binding complex data to the DropDownList, fields should be mapped correctly. Otherwise, the selected item remains undefined.

Binding local data

Local data can be represented in two ways as described below.

1. Array of simple data

The DropDownList has support to load array of primitive data such as strings and numbers. Here, both value and text field act the same.

app.component.ts
app.module.ts
main.ts
import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    // specifies the template string for the DropDownList component with change event
    template: `<ejs-dropdownlist id='ddlelement' #samples [dataSource]='data' [placeholder]='placeholder'></ejs-dropdownlist>`
})
export class AppComponent {
    constructor() {
    }
    // defined the array of data
    public data: string[] = ['Badminton', 'Basketball', 'Cricket', 'Golf', 'Hockey', 'Rugby'];
    // set placeholder text to DropDownList input element
    public placeholder: string = 'Select a game';
}
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { DropDownListModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, DropDownListModule, ButtonModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})
export class AppModule { }
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

import 'zone.js';
enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);

2. Array of JSON data

The DropDownList can generate its list items through an array of complex data. For this,
the appropriate columns should be mapped to the fields
property.

In the following example, Id column and Game column from complex data have been mapped to the value field and text field, respectively.

app.component.ts
app.module.ts
main.ts
import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    // specifies the template string for the DropDownList component with change event
    template: `<ejs-dropdownlist id='ddlelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text'></ejs-dropdownlist>`
})
export class AppComponent {
    constructor() {
    }
    // defined the array of data
    public data: { [key: string]: Object }[] = [ { Id: 'game1', Game: 'Badminton' },
                 { Id: 'game2', Game: 'Football' }, { Id: 'game3', Game: 'Tennis' }];
    // maps the appropriate column to fields property
    public fields: Object = { text: 'Game', value: 'Id' };
    //set the placeholder to DropDownList input
    public text: string = "Select a game";
}
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { DropDownListModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, DropDownListModule, ButtonModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})
export class AppModule { }
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

import 'zone.js';
enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);

3. Array of Complex data

The DropDownList can generate its list items through an array of complex data. For this,
the appropriate columns should be mapped to the fields property.

In the following example, Code.Id column and Country.Name column from complex data have been mapped to the value field and text field, respectively.

app.component.ts
app.module.ts
main.ts
import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    // specifies the template string for the DropDownList component with change event
    template: `<ejs-dropdownlist id='ddlelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text'></ejs-dropdownlist>`
})
export class AppComponent {
    constructor() {
    }
    // defined the array of data
    public data: { [key: string]: Object }[] = [
        { Country: { Name: 'Australia' }, Code: { Id: 'AU' }},
        { Country: { Name: 'Bermuda' },Code: { Id: 'BM' }},
        { Country:{ Name: 'Canada'}, Code:{ Id: 'CA'} },
        { Country:{Name: 'Cameroon'}, Code:{ Id: 'CM'} },
        { Country:{Name: 'Denmark'}, Code:{ Id: 'DK' }},
        { Country:{Name: 'France'}, Code: { Id:'FR'} }
    ];
    // maps the appropriate column to fields property
    public fields: Object = { text: 'Country.Name', value: 'Code.Id' };
    //set the placeholder to DropDownList input
    public text: string = "Select a country";
}
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { DropDownListModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, DropDownListModule, ButtonModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})
export class AppModule { }
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

import 'zone.js';
enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);

Binding remote data

The DropDownList supports retrieval of data from remote data services with the help
of DataManager component. The Query property is used to fetch data from the database and bind it to the DropDownList.

The following sample displays the first 6 contacts from “Customers” table of the Northwind Data Service.

app.component.ts
app.module.ts
main.ts
import { Component } from '@angular/core';
import { Query, DataManager, ODataV4Adaptor } from '@syncfusion/ej2-data'

@Component({
    selector: 'app-root',
    // specifies the template string for the DropDownList component with change event
    template: `<ejs-dropdownlist id='ddlelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text' [query]='query' [sortOrder]='sorting'></ejs-dropdownlist>`
})
export class AppComponent {
    constructor() {
    }
    //bind the DataManager instance to dataSource property
    public data: DataManager = new DataManager({
            url: 'https://services.odata.org/V4/Northwind/Northwind.svc/',
            adaptor: new ODataV4Adaptor,
            crossDomain: true
        });
    // maps the appropriate column to fields property
    public fields: Object = { text: 'ContactName', value: 'CustomerID' };
    //bind the Query instance to query property
    public query: Query = new Query().from('Customers').select(['ContactName', 'CustomerID']).take(6);
    //set the placeholder to DropDownList input
    public text: string = "Select a customer";
    //sort the result items
    public sorting: string = 'Ascending';
}
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
import { DropDownListModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, DropDownListModule, ButtonModule
    ],
    declarations: [AppComponent],
    bootstrap: [AppComponent]
})
export class AppModule { }
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

import 'zone.js';
enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);

Data binding using Async pipe

An Observable is used extensively by Angular since it provide significant benefits over techniques for event handling, asynchronous programming, and handling multiple values.

DropDownList data can be consumed from an Observable object by piping it through an async pipe. The async pipe is used to subscribe the observable object and resolve with the latest value emitted by it.

[app.component.ts]

import { Component, ViewChild } from '@angular/core';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { HttpClient } from '@angular/common/http';

@Component({
    selector: 'app-root',
    // specifies the template string for the DropDownList component with dataSource
    template: `<ejs-dropdownlist  id='customers2' formControlName="skillname" name="skillname" #remote2 [dataSource]='data | async'  [fields]='remoteFields' [placeholder]='remoteWaterMark' ></ejs-dropdownlist >`,
})
export class AppComponent {
    constructor(private http: HttpClient){
      this.data=this.http.get<{[key: string]:object;}[]>('https://services.odata.org/V4/Northwind/Northwind.svc/Customers').pipe(
      map((results : {[key: string]:any;}) => {
        return results['value'];
      })
    );
  }

 public data: Observable<any>;

  // maps the remote data column to fields property
  public remoteFields: Object = { value: 'CustomerID' };

  // set the placeholder to DropDownList input element
  public remoteWaterMark: string = 'Select a customer';
}

[app.module.ts]

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';
import { DropDownListModule, AutoCompleteModule} from '@syncfusion/ej2-angular-dropdowns';
import { AppComponent } from './app.component';
import {DialogModule} from '@syncfusion/ej2-angular-popups';
import { ReactiveFormsModule }   from '@angular/forms';
@NgModule({
  imports: [ 
    BrowserModule, 
    FormsModule,
    DropDownListModule,
    AutoCompleteModule,
    DialogModule,
    HttpClientModule,
    ReactiveFormsModule
    ],
  declarations: [ AppComponent ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

[main.ts]

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { enableProdMode } from '@angular/core';
import { AppModule } from './app.module';

enableProdMode();
platformBrowserDynamic().bootstrapModule(AppModule);

View Sample in Github