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Data Binding in Angular ComboBox component

14 Apr 2021 / 6 minutes to read

The ComboBox 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.

The ComboBox 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 DataManager adaptors.

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

Source

Preview

app.component.ts

app.module.ts

main.ts

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

@Component({
selector: 'app-root',
// specifies the template string for the ComboBox component
template: `<ejs-combobox id='comboelement' #samples [dataSource]='data' [placeholder]='text'></ejs-combobox>`
})
export class AppComponent {
constructor() {
}
// defined the array of data
public data: string[] = ['Badminton', 'Basketball', 'Cricket', 'Golf', 'Hockey', 'Rugby'];
// set placeholder text to ComboBox input element
public text: string = 'Select a game';
}

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { ComboBoxModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, ComboBoxModule,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';

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

2. Array of JSON data

The ComboBox 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.

Source

Preview

app.component.ts

app.module.ts

main.ts

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

@Component({
selector: 'app-root',
// specifies the template string for the ComboBox component with change event
template: `<ejs-combobox id='comboelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text'></ejs-combobox>`
})
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 ComboBox input
public text: string = "Select a game";
}

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { ComboBoxModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, ComboBoxModule,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';

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

3. Array of Complex data

The ComboBox 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.

Source

Preview

app.component.ts

app.module.ts

main.ts

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

@Component({
selector: 'app-root',
// specifies the template string for the ComboBox component with change event
template: `<ejs-combobox id='comboelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text'></ejs-combobox>`
})
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 ComboBox input
public text: string = "Select a country";
}

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { ComboBoxModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, ComboBoxModule,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';

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

Binding remote data

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

In the following sample, displayed first 6 contacts from customer table of Northwind Data Service.

Source

Preview

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 ComboBox component with change event
template: `<ejs-combobox id='comboelement' #samples [dataSource]='data' [fields]='fields' [placeholder]='text' [query]='query' [sortOrder]='sorting'></ejs-combobox>`
})
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 ComboBox 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 { AppComponent } from './app.component';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { ComboBoxModule } from '@syncfusion/ej2-angular-dropdowns';
import { ButtonModule } from '@syncfusion/ej2-angular-buttons';
/**
 * Module
 */
@NgModule({
    imports: [
        BrowserModule,FormsModule, ReactiveFormsModule, ComboBoxModule,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';

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.

ComboBox 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.

Source

Preview

app.component.ts

app.module.ts

main.ts

import { Component } from '@angular/core';
import { Observable } from 'rxjs';
import { CategoriesService } from './categories.service';
import { map } from 'rxjs/operators';
import { HttpClient } from '@angular/common/http';

@Component({
selector: 'app-root',
// specifies the template string for the ComboBox component with dataSource
template: ` <ejs-combobox  id='customers2' formControlName="skillname" name="skillname" #remote2 [dataSource]='data | async'  [fields]='remoteFields' [placeholder]='remoteWaterMark' ></ejs-combobox >`,
providers: [CategoriesService]
})
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]:object;}) => {
    return results.value;
  })
);
  }

 public data: Observable<any>;

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

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

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

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

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

Data Binding in Angular ComboBox component

Binding local data

1. Array of simple data

2. Array of JSON data

3. Array of Complex data

Binding remote data

Data binding using Async pipe

See Also