Deferred Selection
If you enable deferred row selection, the grid does not request selected rows' data with every selection change. For example, if a user clicks the checkbox in the column header to select all the rows, the grid does not immediately fetch all data from the server. This is helpful in the following cases:
- You process data on the server and do not want to load the selected rows' data.
- You do process selected records on the client, but want to reduce the number of requests that are sent.
This demo illustrates the second scenario. Deferred selection is enabled and the selected rows are only requested when you click the button below the grid.
To enable deferred selection in your application, set the selection.deferred property to true.
To specify the initially selected rows, use the selectionFilter property. The DataGrid updates this property's value at runtime and you can always access the applied filter. In this demo, the selectionFilter selects rows whose Status is Completed.
To load the selected rows' data, call the getSelectedRowsData() method. In deferred selection mode, this method returns a Promise. You can access row data in its fulfillment handler. In this demo, the getSelectedRowsData() method gets data objects that are then used to calculate statistics for the selected tasks.
Feel free to share demo-related thoughts here.
If you have technical questions, please create a support ticket in the DevExpress Support Center.
If you have technical questions, please create a support ticket in the DevExpress Support Center.
Thank you!
We appreciate your feedback.
We appreciate your feedback.
<dx-data-grid
id="grid-container"
[dataSource]="dataSource"
[selectionFilter]="['Task_Status', '=', 'Completed']"
[showBorders]="true">
<dxo-selection
mode="multiple"
[deferred]="true"
></dxo-selection>
<dxo-filter-row
[visible]="true"
></dxo-filter-row>
<dxi-column
caption="Subject"
dataField="Task_Subject"
></dxi-column>
<dxi-column
caption="Start Date"
dataField="Task_Start_Date"
width="auto"
dataType="date"
></dxi-column>
<dxi-column
caption="Due Date"
dataField="Task_Due_Date"
width="auto"
dataType="date"
></dxi-column>
<dxi-column
caption="Assigned To"
dataField="ResponsibleEmployee.Employee_Full_Name"
width="auto"
[allowSorting]="false"
></dxi-column>
<dxi-column
caption="Status"
dataField="Task_Status"
width="auto"
></dxi-column>
</dx-data-grid>
<div class="selection-summary center">
<dx-button
id="calculateButton"
text="Get statistics on the selected tasks"
type="default"
(onClick)="calculateStatistics()"
></dx-button>
<div>
<div class="column">
<span class="text count">Task count:</span>
<span class="value">{{taskCount}}</span>
</div>
<div class="column">
<span class="text people-count">People assigned:</span>
<span class="value">{{peopleCount}}</span>
</div>
<div class="column">
<span class="text avg-duration">Average task duration (days):</span>
<span class="value">{{avgDuration}}</span>
</div>
</div>
</div>
import { NgModule, Component, ViewChild, AfterViewInit, enableProdMode } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { DxDataGridModule, DxDataGridComponent, DxButtonModule } from 'devextreme-angular';
import query from 'devextreme/data/query';
import 'devextreme/data/odata/store';
if(!/localhost/.test(document.location.host)) {
enableProdMode();
}
@Component({
selector: 'demo-app',
templateUrl: 'app/app.component.html',
styleUrls: ['app/app.component.css'],
preserveWhitespaces: true
})
export class AppComponent implements AfterViewInit {
@ViewChild(DxDataGridComponent, { static: false }) dataGrid: DxDataGridComponent;
MILLISECONDS_IN_DAY = 1000 * 60 * 60 * 24;
dataSource: any = {
store: {
type: "odata",
url: "https://js.devexpress.com/Demos/DevAV/odata/Tasks",
key: "Task_ID"
},
expand: "ResponsibleEmployee",
select: [
"Task_ID",
"Task_Subject",
"Task_Start_Date",
"Task_Due_Date",
"Task_Status",
"ResponsibleEmployee/Employee_Full_Name"
]
};
taskCount = 0;
peopleCount = 0;
avgDuration = 0;
ngAfterViewInit() {
this.calculateStatistics();
}
calculateStatistics() {
this.dataGrid.instance.getSelectedRowsData().then((rowData) => {
var commonDuration = 0;
for (var i = 0; i < rowData.length; i++) {
commonDuration += rowData[i].Task_Due_Date - rowData[i].Task_Start_Date;
}
commonDuration = commonDuration / this.MILLISECONDS_IN_DAY;
this.taskCount = rowData.length;
this.peopleCount = query(rowData)
.groupBy("ResponsibleEmployee.Employee_Full_Name")
.toArray()
.length;
this.avgDuration = Math.round(commonDuration / rowData.length) || 0;
});
}
}
@NgModule({
imports: [
BrowserModule,
DxDataGridModule,
DxButtonModule
],
declarations: [AppComponent],
bootstrap: [AppComponent]
})
export class AppModule { }
platformBrowserDynamic().bootstrapModule(AppModule);
::ng-deep #grid-container {
height: 400px;
}
::ng-deep .center {
text-align: center;
}
::ng-deep .selection-summary {
border: 1px solid rgba(161, 161,161, 0.2);
padding: 25px;
}
::ng-deep .column {
margin: 20px 30px 0 0;
display: inline-block;
white-space: nowrap;
text-align: right;
}
::ng-deep .value {
font-size: 40px;
display: inline-block;
vertical-align: middle;
}
::ng-deep .text {
text-align: left;
white-space: normal;
display: inline-block;
vertical-align: middle;
}
::ng-deep .avg-duration {
width: 100px;
}
::ng-deep .count{
width: 40px;
}
::ng-deep .people-count {
width: 65px;
}
// In real applications, you should not transpile code in the browser. You can see how to create your own application with Angular and DevExtreme here:
// https://js.devexpress.com/Documentation/Guide/Angular_Components/Getting_Started/Create_a_DevExtreme_Application/
System.config({
transpiler: 'ts',
typescriptOptions: {
module: "system",
emitDecoratorMetadata: true,
experimentalDecorators: true
},
meta: {
'typescript': {
"exports": "ts"
},
'devextreme/localization.js': {
"esModule": true
}
},
paths: {
'npm:': 'https://unpkg.com/'
},
map: {
'ts': 'npm:plugin-typescript@8.0.0/lib/plugin.js',
'typescript': 'npm:typescript@3.5.3/lib/typescript.js',
'@angular': 'npm:@angular',
'tslib': 'npm:tslib@2.1.0/tslib.js',
'rxjs': 'npm:rxjs@6.4.0',
'rrule': 'npm:rrule@2.6.6/dist/es5/rrule.js',
'luxon': 'npm:luxon@1.26.0/build/global/luxon.min.js',
'es6-object-assign': 'npm:es6-object-assign@1.1.0',
'devextreme': 'npm:devextreme@20.2.6',
'jszip': 'npm:jszip@3.6.0/dist/jszip.min.js',
'devextreme-quill': 'npm:devextreme-quill@0.10.3/dist/dx-quill.min.js',
'devexpress-diagram': 'npm:devexpress-diagram@2.0.18',
'devexpress-gantt': 'npm:devexpress-gantt@2.0.24',
'devextreme-angular': 'npm:devextreme-angular@20.2.6',
'preact': 'npm:preact@10.5.13/dist/preact.js',
'preact/hooks': 'npm:preact@10.5.13/hooks/dist/hooks.js'
},
packages: {
'app': {
main: './app.component.ts',
defaultExtension: 'ts'
},
'devextreme': {
defaultExtension: 'js'
},
'devextreme/events/utils': {
main: 'index'
},
'devextreme/events': {
main: 'index'
},
'es6-object-assign': {
main: './index.js',
defaultExtension: 'js'
}
},
packageConfigPaths: [
"npm:@angular/*/package.json",
"npm:@angular/common/*/package.json",
"npm:rxjs/package.json",
"npm:rxjs/operators/package.json",
"npm:devextreme-angular/*/package.json",
"npm:devextreme-angular/ui/*/package.json",
"npm:devextreme-angular/package.json",
"npm:devexpress-diagram/package.json",
"npm:devexpress-gantt/package.json",
]
});
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>DevExtreme Demo</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0" />
<link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/20.2.6/css/dx.common.css" />
<link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/20.2.6/css/dx.light.css" />
<script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
<script src="https://unpkg.com/zone.js@0.10.2/dist/zone.js"></script>
<script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
<script src="https://unpkg.com/systemjs@0.21.3/dist/system.js"></script>
<script src="config.js"></script>
<script>
System.import('app').catch(console.error.bind(console));
</script>
</head>
<body class="dx-viewport">
<div class="demo-container">
<demo-app>Loading...</demo-app>
</div>
</body>
</html>