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Data Grid

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 option to true.

To specify the initially selected rows, use the selectionFilter option. The widget updates this option'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.

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import React from 'react'; import DataGrid, { Column, FilterRow, Selection } from 'devextreme-react/data-grid'; import Button from 'devextreme-react/button'; import query from 'devextreme/data/query'; import 'devextreme/data/odata/store'; var dataGrid; const MILLISECONDS_IN_DAY = 1000 * 60 * 60 * 24; const dataSource = { 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' ] }; const selectionFilter = ['Task_Status', '=', 'Completed']; class App extends React.Component { constructor(props) { super(props); this.state = { taskCount: 0, peopleCount: 0, avgDuration: 0 }; this.onInitialized = this.onInitialized.bind(this); this.calculateStatistics = this.calculateStatistics.bind(this); } render() { return ( <div> <DataGrid id="grid-container" dataSource={dataSource} showBorders={true} defaultSelectionFilter={selectionFilter} onInitialized={this.onInitialized} > <Selection mode="multiple" deferred={true} /> <FilterRow visible={true} /> <Column caption="Subject" dataField="Task_Subject" /> <Column caption="Start Date" dataField="Task_Start_Date" width="auto" dataType="date" /> <Column caption="Due Date" dataField="Task_Due_Date" width="auto" dataType="date" /> <Column caption="Assigned To" dataField="ResponsibleEmployee.Employee_Full_Name" width="auto" allowSorting={false} /> <Column caption="Status" width="auto" dataField="Task_Status" /> </DataGrid> <div className="selection-summary center"> <Button id="calculateButton" text="Get statistics on the selected tasks" type="default" onClick={this.calculateStatistics} /> <div> <div className="column"> <span className="text count">Task count:</span> &nbsp; <span className="value">{this.state.taskCount}</span> </div> &nbsp; <div className="column"> <span className="text people-count">People assingned:</span> &nbsp; <span className="value">{this.state.peopleCount}</span> </div> &nbsp; <div className="column"> <span className="text avg-duration">Average task duration (days):</span> &nbsp; <span className="value">{this.state.avgDuration}</span> </div> </div> </div> </div> ); } onInitialized(e) { dataGrid = e.component; this.calculateStatistics(); } calculateStatistics() { dataGrid.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 / MILLISECONDS_IN_DAY; this.setState({ taskCount: rowData.length, peopleCount: query(rowData) .groupBy('ResponsibleEmployee.Employee_Full_Name') .toArray() .length, avgDuration: Math.round(commonDuration / rowData.length) || 0 }); }); } } export default App;
import React from 'react'; import ReactDOM from 'react-dom'; import App from './App.js'; ReactDOM.render( <App />, document.getElementById('app') );
<!DOCTYPE html> <html> <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/20.1.7/css/dx.common.css" /> <link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/20.1.7/css/dx.light.css" /> <link rel="stylesheet" type="text/css" href="styles.css" /> <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script> <script src="https://unpkg.com/systemjs@0.21.3/dist/system.js"></script> <script type="text/javascript" src="config.js"></script> <script type="text/javascript"> System.import('./index.js'); </script> </head> <body class="dx-viewport"> <div class="demo-container"> <div id="app"></div> </div> </body> </html>
#grid-container { height: 400px; } .center { text-align: center; } .selection-summary { border: 1px solid rgba(161, 161,161, 0.2); padding: 25px; } .column { margin: 20px 30px 0 0; display: inline-block; white-space: nowrap; text-align: right; } .value { font-size: 40px; display: inline-block; vertical-align: middle; } .text { text-align: left; white-space: normal; display: inline-block; vertical-align: middle; } .avg-duration { width: 100px; } .count{ width: 40px; } .people-count { width: 65px; }
System.config({ transpiler: 'plugin-babel', meta: { }, paths: { 'npm:': 'https://unpkg.com/' }, defaultExtension: 'js', map: { 'react': 'npm:react@16/umd/react.development.js', 'react-dom': 'npm:react-dom@16/umd/react-dom.development.js', 'prop-types': 'npm:prop-types/prop-types.js', 'devextreme': 'npm:devextreme@20.1', 'devextreme-react': 'npm:devextreme-react@20.1', 'jszip': 'npm:jszip@3.1.3/dist/jszip.min.js', 'quill': 'npm:quill@1.3.7/dist/quill.js', 'devexpress-diagram': 'npm:devexpress-diagram@1.0.14', 'devexpress-gantt': 'npm:devexpress-gantt@1.0.7', // SystemJS plugins 'plugin-babel': 'npm:systemjs-plugin-babel@0/plugin-babel.js', 'systemjs-babel-build': 'npm:systemjs-plugin-babel@0/systemjs-babel-browser.js' }, packages: { 'devextreme': { defaultExtension: 'js' }, 'devextreme-react': { main: 'index.js' }, 'devextreme/events/utils': { main: 'index' }, 'devextreme/events': { main: 'index' }, }, babelOptions: { sourceMaps: false, stage0: true, react: true } });