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Remote Data in React TreeGrid component

02 Feb 2023 / 22 minutes to read

To bind remote data to TreeGrid component, assign service data as an instance of DataManager to the dataSource property. To interact with remote data source, provide the endpoint url and define the hasChildMapping property of treegrid.

The hasChildMapping property maps the field name in data source, that denotes whether current record holds any child records. This is useful internally to show expand icon while binding child data on demand.

The TreeGrid provides Load on Demand support for rendering remote data. The Load on demand is considered in TreeGrid for the following actions.

  • Expanding root nodes.
  • Navigating pages, with paging enabled in TreeGrid.

When load on demand is enabled, all the root nodes are rendered in collapsed state at initial load.

When load on demand support is enabled in TreeGrid with paging, the current or active page’s root node alone will be rendered in collapsed state. On expanding the root node, the child nodes will be loaded from the remote server.

When a root node is expanded, its child nodes are rendered and are cached locally, such that on consecutive expand/collapse actions on root node, the child nodes are loaded from the cache instead from the remote server.

Similarly, if the user navigates to a new page, the root nodes of that specific page, will be rendered with request to the remote server.

Remote Data Binding supports only Self-Referential Data and by default the pageSizeMode for Remote Data is Root mode. i.e only root node’s count will be shown in pager while using Remote Data

Source
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App.jsx
App.tsx
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import { DataManager, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, Page, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
    const data = new DataManager({
        adaptor: new WebApiAdaptor,
        crossDomain: true,
        url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
    });
    return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' allowPaging={true}>
    <ColumnsDirective>
        <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
        <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
        <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date'/>
        <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right'/>
    </ColumnsDirective>
    <Inject services={[Page]}/>
</TreeGridComponent>;
}
;
export default App;
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import { DataManager, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, Page, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
const data = new DataManager({
    adaptor: new WebApiAdaptor,
    crossDomain: true,
    url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
});
return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' allowPaging={true}>
    <ColumnsDirective>
        <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
        <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
        <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date' />
        <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
    </ColumnsDirective>
    <Inject services={[Page]}/>
</TreeGridComponent>
};
export default App;

By default, DataManager uses ODataAdaptor for remote data-binding. Based on the RESTful web services, set the corresponding adaptor to DataManager. Refer here for more details. Filtering and searching server-side data operations are not supported in load on demand

LoadChildOnDemand

While binding remote data to Tree Grid component, by default Tree Grid renders parent rows in collapsed state. Tree Grid provides option to load the child records also during the initial rendering itself for remote data binding by setting loadChildOnDemand as true.

When loadChildOnDemand is enabled parent records are rendered in expanded state.

The following code example describes the behavior of the loadChildOnDemand feature of Tree Grid.

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import { DataManager, UrlAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';

function App() {

const dataManager: DataManager = new DataManager({
    adaptor: new UrlAdaptor,
    insertUrl: "Home/Insert",
    removeUrl: "Home/Delete",
    updateUrl: "Home/Update",
    batchUrl: "Home/Remove",
    url: "Home/DataSource",
});
return <TreeGridComponent dataSource={dataManager} treeColumnIndex={1} idMapping= 'TaskID'
parentIdMapping='parentID' loadChildOnDemand='true' height='270' allowPaging='true'>
    <ColumnsDirective>
        <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
        <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
        <ColumnDirective field='StartDate' headerText='Start Date' width='90' textAlign='Right' format='yMd' type='date' />
        <ColumnDirective field='EndDate' headerText='End Date' width='90' format='yMd' textAlign='Right' />
        <ColumnDirective field='Priority' headerText='Priority' width='110'/>
    </ColumnsDirective>
</TreeGridComponent>
};
export default App;

Also while using loadChildOnDemand we need to handle the child records on server end and it is applicable to CRUD operations also.

The following code example describes handling of child records at server end.

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public ActionResult UrlDatasource(DataManagerRequest dm)
{
if (TreeData.tree.Count == 0)
      TreeData.GetTree();
IEnumerable DataSource = TreeData.tree;

DataOperations operation = new DataOperations();
if (dm.Where != null && dm.Where.Count > 0)
{
    DataSource = operation.PerformFiltering(DataSource, dm.Where, "and");    //perform filtering
}
if (dm.Sorted != null && dm.Sorted.Count > 0)
{
    DataSource = operation.PerformSorting(DataSource, dm.Sorted);  //perform sorting
}
var count = DataSource.ToList<TreeData>().Count();
if (dm.Skip != 0)
{
    DataSource = operation.PerformSkip(DataSource, dm.Skip);   //Paging
}
if (dm.Take != 0)
{
    DataSource = operation.PerformTake(DataSource, dm.Take);
}
if (dm.Where != null)
{
    DataSource = CollectChildRecords(DataSource, dm);  // method to collect child records
}

return dm.RequiresCounts ? Json(new { result = DataSource, count = count }) : Json(DataSource);
}

 public IEnumerable CollectChildRecords(IEnumerable datasource, DataManagerRequest dm)
 {
 DataOperations operation = new DataOperations();
 IEnumerable DataSource = TreeData.tree;   // use the total DataSource here
 string IdMapping = "TaskID";     // define your IdMapping field name here
 int[] TaskIds = new int[0];
 foreach (var rec in datasource)
 {
    int taskid = (int)rec.GetType().GetProperty(IdMapping).GetValue(rec);
    TaskIds = TaskIds.Concat(new int[] { taskid }).ToArray();  //get the Parentrecord Ids based on IdMapping Field
 }
IEnumerable ChildRecords = null;
 foreach (int id in TaskIds)
 {
    dm.Where[0].value = id;
    IEnumerable records = operation.PerformFiltering(DataSource, dm.Where, dm.Where[0].Operator);   //perform filtering to collect the childrecords based on Ids
    ChildRecords = ChildRecords == null || (ChildRecords.AsQueryable().Count() == 0) ? records : ((IEnumerable<object>)ChildRecords).Concat((IEnumerable<object>)records);  //concate the childrecords with dataSource
 }
 if (ChildRecords != null)
 {
    ChildRecords = CollectChildRecords(ChildRecords, dm);  // repeat the operation for inner level child
    if (dm.Sorted != null && dm.Sorted.Count > 0) // perform Sorting
    {
        ChildRecords = operation.PerformSorting(ChildRecords, dm.Sorted);
    }
    datasource = ((IEnumerable<object>)datasource).Concat((IEnumerable<object>)ChildRecords);  //concate the childrecords with dataSource
 }
return datasource;
 }

Offline mode

On remote data binding, all treegrid actions such as paging, loading child on-demand, will be processed on server-side. To avoid postback, set the treegrid to load all data on initialization and make the actions process in client-side. To enable this behavior, use the offline property of DataManager.

Source
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App.jsx
App.tsx
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import { DataManager, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, Page, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
    const data = new DataManager({
        adaptor: new WebApiAdaptor,
        crossDomain: true,
        offline: true,
        url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
    });
    return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' allowPaging={true}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date'/>
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right'/>
        </ColumnsDirective>
        <Inject services={[Page]}/>
    </TreeGridComponent>;
}
;
export default App;
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import { DataManager, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, Page, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
const data = new DataManager({
    adaptor: new WebApiAdaptor,
    crossDomain: true,
    offline: true,
    url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
});
    return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1}
    idMapping='TaskID' parentIdMapping='ParentItem' height='260' allowPaging={true}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date' />
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
        </ColumnsDirective>
        <Inject services={[Page]}/>
    </TreeGridComponent>
};
export default App;

Custom adaptor

You can create your own adaptor by extending the built-in adaptors. The following demonstrates custom adaptor approach and how to add a serial number for the records by overriding the built-in response processing using the processResponse method of the ODataAdaptor.

Source
Preview
App.jsx
serialNoAdaptor.jsx
App.tsx
serialNoAdaptor.tsx
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import { DataManager } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
import { SerialNoAdaptor } from './serialNoAdaptor';
export default class App extends React.Component {
    constructor() {
        super(...arguments);
        this.data = new DataManager({
            adaptor: new SerialNoAdaptor,
            crossDomain: true,
            url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
        });
    }
    render() {
        return <TreeGridComponent dataSource={this.data} hasChildMapping='isParent' treeColumnIndex={2} idMapping='TaskID' parentIdMapping='ParentItem' height='260'>
        <ColumnsDirective>
          <ColumnDirective field='Sno' headerText='Sno' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date'/>
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right'/>
        </ColumnsDirective>
    </TreeGridComponent>;
    }
}
;
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import { setValue } from '@syncfusion/ej2-base';
import { ODataAdaptor } from '@syncfusion/ej2-data';
export class SerialNoAdaptor extends ODataAdaptor {
    processResponse() {
        let i = 0;
        // calling base class processResponse function
        const original = super.processResponse.apply(this, arguments);
        if (!(original instanceof Array)) {
            // adding serial number
            original.result.forEach((item) => setValue('Sno', ++i, item));
        }
        return original;
    }
}
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import { DataManager } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
import { SerialNoAdaptor } from './serialNoAdaptor';

export default class App extends React.Component<{}, {}>{
public data = new DataManager({
    adaptor: new SerialNoAdaptor,
    crossDomain: true,
    url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
});
public render() {
    return <TreeGridComponent dataSource={this.data} hasChildMapping='isParent' treeColumnIndex={2} idMapping='TaskID' parentIdMapping='ParentItem' height='260'>
        <ColumnsDirective>
          <ColumnDirective field='Sno' headerText='Sno' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date' />
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
        </ColumnsDirective>
    </TreeGridComponent>
}
};
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import { setValue } from '@syncfusion/ej2-base';
import { ODataAdaptor } from '@syncfusion/ej2-data';

export class SerialNoAdaptor extends ODataAdaptor {
    public processResponse() {
        let i: number = 0;
        // calling base class processResponse function
        const original: any = super.processResponse.apply(this, arguments);
        if (!(original instanceof Array)) {
            // adding serial number
            original.result.forEach((item: object) =>  setValue('Sno', ++i, item));
        }
        return original;
    }
}

Sending additional parameters to the server

To add a custom parameter to the data request, use the addParams method of Query class. Assign the Query object with additional parameters to the treegrid query property.

Source
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App.jsx
App.tsx
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import { DataManager, Query, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
    const data = new DataManager({
        adaptor: new WebApiAdaptor,
        crossDomain: true,
        url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
    });
    const query = new Query().addParams('ej2treegrid', 'true');
    return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' query={query}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date'/>
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right'/>
        </ColumnsDirective>
    </TreeGridComponent>;
}
;
export default App;
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import { DataManager, Query, WebApiAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';

function App() {
const data = new DataManager({
    adaptor: new WebApiAdaptor,
    crossDomain: true,
    url: 'https://ej2services.syncfusion.com/production/web-services/api/SelfReferenceData'
});

const query = new Query().addParams('ej2treegrid', 'true');
    return <TreeGridComponent dataSource={data} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' query={query}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date' />
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
        </ColumnsDirective>
    </TreeGridComponent>
};
export default App;

Handling HTTP error

During server interaction from the treegrid, some server-side exceptions may occur, and you can acquire those error messages or exception details in client-side using the actionFailure event.

The argument passed to the actionFailure event contains the error details returned from the server.

Source
Preview
App.jsx
App.tsx
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import { DataManager } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';
function App() {
    let treegrid;
    const data = new DataManager({
        url: 'http://some.com/invalidUrl'
    });
    const onActionFailure = (e) => {
        const span = document.createElement('span');
        if (treegrid) {
            treegrid.element.parentNode
                .insertBefore(span, treegrid.element);
            span.style.color = "#FF0000";
            span.innerHTML = "Server exception: 404 Not found";
        }
    };
    return <TreeGridComponent dataSource={data} ref={g => treegrid = g} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' actionFailure={onActionFailure}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date'/>
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right'/>
        </ColumnsDirective>
    </TreeGridComponent>;
}
;
export default App;
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import { DataManager } from '@syncfusion/ej2-data';
import { FailureEventArgs } from '@syncfusion/ej2-grids';
import { ColumnDirective, ColumnsDirective, TreeGrid, TreeGridComponent } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';

function App() {
let treegrid: TreeGridComponent | null;
const data = new DataManager({
    url: 'http://some.com/invalidUrl'
});
const onActionFailure = (e: FailureEventArgs) => {
    const span: HTMLElement = document.createElement('span');
    if (treegrid) {
        (treegrid.element.parentNode as HTMLElement)
            .insertBefore(span, treegrid.element);
        span.style.color = "#FF0000";
        span.innerHTML = "Server exception: 404 Not found";
    }
}
    return <TreeGridComponent dataSource={data} ref={g => treegrid = g} hasChildMapping='isParent' treeColumnIndex={1} idMapping='TaskID' parentIdMapping='ParentItem' height='260' actionFailure={onActionFailure}>
        <ColumnsDirective>
            <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right'/>
            <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
            <ColumnDirective field='StartDate' headerText='Start Date' width='90' format='yMd' textAlign='Right' type='date' />
            <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
        </ColumnsDirective>
    </TreeGridComponent>
};
export default App;

The actionFailure event will be triggered not only for the server errors, but also when there is an exception while processing the treegrid actions.

Load on demand with virtualization

While binding remote data to Tree Grid component, by default Tree Grid renders parent rows in collapsed state. When expanding the root node, the child nodes will be loaded from the remote server.

When using virtualization with remote data binding, it helps you to improve the tree grid performance while loading a large set of data by setting enableVirtualization as true. The Tree Grid UI virtualization allows it to render only rows and columns visible within the view-port without buffering the entire datasource.

hasChildMapping property maps the field name in data source, that denotes whether current record holds any child records. This is useful internally to show expand icon while binding child data on demand.

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import { DataManager, UrlAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, TreeGridComponent, VirtualScroll, Sort, Filter, Edit, EditSettingsModel, Toolbar, ToolbarItems, PageSettingsModel } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';

function App() {

const editOptions: EditSettingsModel = {
    allowAdding: true,
    allowDeleting: true,
    allowEditing: true,
    mode: 'Row',
    newRowPosition: 'Below'
};
const toolbarOptions: ToolbarItems[] = ['Add', 'Edit', 'Delete', 'Update', 'Cancel'];

const pageSettings: PageSettingsModel = { pageSize: 30 };

const dataManager: DataManager = new DataManager({
    adaptor: new UrlAdaptor,
    insertUrl: "Home/Insert",
    removeUrl: "Home/Delete",
    updateUrl: "Home/Update",
    url: "Home/DataSource",
});
return <TreeGridComponent dataSource={dataManager} treeColumnIndex={1} idMapping= 'TaskID'
parentIdMapping='ParentValue' hasChildMapping='isParent' expandStateMapping='IsExpanded' height='400' enableVirtualization={true} editSettings={editOptions} toolbar={toolbarOptions} allowFiltering={true} allowSorting={true} pageSettings={pageSettings}>
    <ColumnsDirective>
        <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right' isPrimaryKey={true}/>
        <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
        <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
    </ColumnsDirective>
    <Inject services={[Edit, VirtualScroll, Sort, Filter, Toolbar]} />
</TreeGridComponent>
};
export default App;

The following code example describes handling of Load on demand at server end.

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public ActionResult lazyLoading()
{
TreeData.tree = new List<TreeData>();
return View();
}
public ActionResult UrlDatasource(DataManagerRequest dm)
{
List<TreeData> data = new List<TreeData>();
data = TreeData.GetTree();
DataOperations operation = new DataOperations();
IEnumerable<TreeData> DataSource = data;
List<TreeData> ExpandedParentRecords = new List<TreeData>();
if (dm.Expand != null && dm.Expand[0] == "ExpandingAction") // setting the ExpandStateMapping property whether is true or false
{
    var val = TreeData.GetTree().Where(ds => ds.TaskID == int.Parse(dm.Expand[1])).FirstOrDefault();
    val.IsExpanded = true;
}
else if (dm.Expand != null && dm.Expand[0] == "CollapsingAction")
{
    var val = TreeData.GetTree().Where(ds => ds.TaskID == int.Parse(dm.Expand[1])).FirstOrDefault();
    val.IsExpanded = false;
}
if (!(dm.Where != null && dm.Where.Count > 1))
{
    data = data.Where(p => p.ParentValue == null).ToList();
}
DataSource = data;
if (dm.Search != null && dm.Search.Count > 0) // Searching
{
    DataSource = operation.PerformSearching(DataSource, dm.Search);
}
if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // Sorting
{
    DataSource = operation.PerformSorting(DataSource, dm.Sorted);
}
if (dm.Where != null && dm.Where.Count > 1) //filtering
{
    DataSource = operation.PerformFiltering(DataSource, dm.Where, "and");
}
data = new List<TreeData>();
foreach (var rec in DataSource)
{
    if (rec.IsExpanded)
    {
        ExpandedParentRecords.Add(rec as TreeData); // saving the expanded parent records
    }
    data.Add(rec as TreeData);
}
var GroupData = TreeData.GetTree().ToList().GroupBy(rec => rec.ParentValue)
                    .Where(g => g.Key != null).ToDictionary(g => g.Key?.ToString(), g => g.ToList());
if (ExpandedParentRecords.Count > 0)
{
    foreach (var Record in ExpandedParentRecords.ToList())
    {
        var ChildGroup = GroupData[Record.TaskID.ToString()];
        if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // sorting the child records
        {
            IEnumerable ChildSort = ChildGroup;
            ChildSort = operation.PerformSorting(ChildSort, dm.Sorted);
            ChildGroup = new List<TreeData>();
            foreach (var rec in ChildSort)
            {
                ChildGroup.Add(rec as TreeData);
            }
        }
        if (dm.Search != null && dm.Search.Count > 0) // searching the child records
        {
            IEnumerable ChildSearch = ChildGroup;
            ChildSearch = operation.PerformSearching(ChildSearch, dm.Search);
            ChildGroup = new List<TreeData>();
            foreach (var rec in ChildSearch)
            {
                ChildGroup.Add(rec as TreeData);
            }
        }
        AppendChildren(dm, ChildGroup, Record, GroupData, data);
    }
}
DataSource = data;
if (dm.Expand != null && dm.Expand[0] == "CollapsingAction") // setting the skip index based on collapsed parent
{
    string IdMapping = "TaskID";
    List<WhereFilter> CollapseFilter = new List<WhereFilter>();
    CollapseFilter.Add(new WhereFilter() { Field = IdMapping, value = dm.Where[0].value, Operator = dm.Where[0].Operator });
    var CollapsedParentRecord = operation.PerformFiltering(DataSource, CollapseFilter, "and");
    var index = data.Cast<object>().ToList().IndexOf(CollapsedParentRecord.Cast<object>().ToList()[0]);
    dm.Skip = index;
}
else if (dm.Expand != null && dm.Expand[0] == "ExpandingAction") // setting the skip index based on expanded parent
{
    string IdMapping = "TaskID";
    List<WhereFilter> ExpandFilter = new List<WhereFilter>();
    ExpandFilter.Add(new WhereFilter() { Field = IdMapping, value = dm.Where[0].value, Operator = dm.Where[0].Operator });
    var ExpandedParentRecord = operation.PerformFiltering(DataSource, ExpandFilter, "and");
    var index = data.Cast<object>().ToList().IndexOf(ExpandedParentRecord.Cast<object>().ToList()[0]);
    dm.Skip = index;
}
int count = data.Count;
DataSource = data;
if (dm.Skip != 0)
{
    DataSource = operation.PerformSkip(DataSource, dm.Skip);   //Paging
}
if (dm.Take != 0)
{
    DataSource = operation.PerformTake(DataSource, dm.Take);
}
return dm.RequiresCounts ? Json(new { result = DataSource, count = count }) : Json(DataSource);

}

private void AppendChildren(DataManagerRequest dm, List<TreeData> ChildRecords, TreeData ParentValue, Dictionary<string, List<TreeData>> GroupData, List<TreeData> data) // Getting child records for the respective parent
{
string TaskId = ParentValue.TaskID.ToString();
var index = data.IndexOf(ParentValue);
DataOperations operation = new DataOperations();
foreach (var Child in ChildRecords)
{
    if (ParentValue.IsExpanded)
    {
        string ParentId = Child.ParentValue.ToString();
        if (TaskId == ParentId)
        {
            ((IList)data).Insert(++index, Child);
            if (GroupData.ContainsKey(Child.TaskID.ToString()))
            {
                var DeepChildRecords = GroupData[Child.TaskID.ToString()];
                if (DeepChildRecords?.Count > 0)
                {
                    if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // sorting the child records
                    {
                        IEnumerable ChildSort = DeepChildRecords;
                        ChildSort = operation.PerformSorting(ChildSort, dm.Sorted);
                        DeepChildRecords = new List<TreeData>();
                        foreach (var rec in ChildSort)
                        {
                            DeepChildRecords.Add(rec as TreeData);
                        }
                    }
                    if (dm.Search != null && dm.Search.Count > 0) // searching the child records
                    {
                        IEnumerable ChildSearch = DeepChildRecords;
                        ChildSearch = operation.PerformSearching(ChildSearch, dm.Search);
                        DeepChildRecords = new List<TreeData>();
                        foreach (var rec in ChildSearch)
                        {
                            DeepChildRecords.Add(rec as TreeData);
                        }
                    }
                    AppendChildren(dm, DeepChildRecords, Child, GroupData, data);
                    if (Child.IsExpanded)
                    {
                        index += DeepChildRecords.Count;
                    }
                }
            }
            else
            {
                Child.isParent = false;
            }
        }
    }
}

}

public ActionResult Update(CRUDModel<TreeData> value)
{
List<TreeData> data = new List<TreeData>();
data = TreeData.GetTree();
var val = data.Where(ds => ds.TaskID == value.Value.TaskID).FirstOrDefault();
val.TaskName = value.Value.TaskName;
val.Duration = value.Value.Duration;
return Json(val);
}

public ActionResult Insert(CRUDModel<TreeData> value)
{
var c = 0;
for (; c < TreeData.GetTree().Count; c++)
{
    if (TreeData.GetTree()[c].TaskID == value.RelationalKey)
    {
        if (TreeData.GetTree()[c].isParent == null)
        {
            TreeData.GetTree()[c].isParent = true;
        }
        break;
    }
}
c += FindChildRecords(value.RelationalKey);
TreeData.GetTree().Insert(c + 1, value.Value);

return Json(value.Value);
}

public int FindChildRecords(int? id)
{
var count = 0;
for (var i = 0; i < TreeData.GetTree().Count; i++)
{
    if (TreeData.GetTree()[i].ParentValue == id)
    {
        count++;
        count += FindChildRecords(TreeData.GetTree()[i].TaskID);
    }
}
return count;
}

public object Delete(CRUDModel<TreeData> value)
{
if (value.deleted != null)
{
    for (var i = 0; i < value.deleted.Count; i++)
    {
        TreeData.GetTree().Remove(TreeData.GetTree().Where(ds => ds.TaskID == value.deleted[i].TaskID).FirstOrDefault());
    }
}
else
{
    TreeData.GetTree().Remove(TreeData.GetTree().Where(or => or.TaskID == int.Parse(value.Key.ToString())).FirstOrDefault());
}
return Json(value);
}

public class CRUDModel<T> where T : class
{

public TreeData Value;
public int Key { get; set; }
public int RelationalKey { get; set; }
public List<T> added { get; set; }
public List<T> changed { get; set; }
public List<T> deleted { get; set; }
}

public class TreeData
{
public static List<TreeData> tree = new List<TreeData>();
[System.ComponentModel.DataAnnotations.Key]
public int TaskID { get; set; }
public string TaskName { get; set; }
public int Duration { get; set; }
public int? ParentValue { get; set; }
public bool? isParent { get; set; }
public bool IsExpanded { get; set; }
public TreeData() { }
public static List<TreeData> GetTree()
{
    if (tree.Count == 0)
    {
        int root = 0;
        for (var t = 1; t <= 500; t++)
        {
            Random ran = new Random();
            string math = (ran.Next() % 3) == 0 ? "High" : (ran.Next() % 2) == 0 ? "Release Breaker" : "Critical";
            string progr = (ran.Next() % 3) == 0 ? "Started" : (ran.Next() % 2) == 0 ? "Open" : "In Progress";
            root++;
            int rootItem = root;
            tree.Add(new TreeData() { TaskID = rootItem, TaskName = "Parent task " + rootItem.ToString(), isParent = true, IsExpanded = false, ParentValue = null, Duration = ran.Next(1, 50) });
            int parent = root;
            for (var d = 0; d < 1; d++)
            {
                root++;
                string value = ((parent + 1) % 3 == 0) ? "Low" : "Critical";
                int par = parent + 1;
                progr = (ran.Next() % 3) == 0 ? "In Progress" : (ran.Next() % 2) == 0 ? "Open" : "Validated";
                int iD = root;
                tree.Add(new TreeData() { TaskID = iD, TaskName = "Child task " + iD.ToString(), isParent = true, IsExpanded = false, ParentValue = rootItem, Duration = ran.Next(1, 50) });
                int subparent = root;
                for (var c = 0; c < 500; c++)
                {
                    root++;
                    string val = ((subparent + c + 1) % 3 == 0) ? "Low" : "Critical";
                    int subchild = subparent + c + 1;
                    string progress = (ran.Next() % 3) == 0 ? "In Progress" : (ran.Next() % 2) == 0 ? "Open" : "Validated";
                    int childID = root ;
                    tree.Add(new TreeData() { TaskID = childID, TaskName = "sub Child task " + childID.ToString(), isParent = false, IsExpanded = false, ParentValue = subparent, Duration = ran.Next(1, 50) });
                }
            }
        }
    }
    return tree;
}
}

Load parent rows in expanded state with virtualization

Tree Grid provides an option to load the child records in the initial rendering itself for remote data binding by setting the loadChildOnDemand as true. When the loadChildOnDemand is enabled, parent records are rendered in expanded state.

When using virtualization with loadChildOnDemand , it helps you to improve the tree grid performance while loading the child records during the initial rendering for remote data binding by setting enableVirtualization as true and loadChildOnDemand as true.

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import { DataManager, UrlAdaptor } from '@syncfusion/ej2-data';
import { ColumnDirective, ColumnsDirective, Inject, TreeGridComponent, VirtualScroll, Sort, Filter, Edit, EditSettingsModel, Toolbar, ToolbarItems, PageSettingsModel } from '@syncfusion/ej2-react-treegrid';
import * as React from 'react';
import './App.css';

function App() {

const editOptions: EditSettingsModel = {
    allowAdding: true,
    allowDeleting: true,
    allowEditing: true,
    mode: 'Row',
    newRowPosition: 'Below'
};
const toolbarOptions: ToolbarItems[] = ['Add', 'Edit', 'Delete', 'Update', 'Cancel'];

const pageSettings: PageSettingsModel = { pageSize: 30 };

const dataManager: DataManager = new DataManager({
    adaptor: new UrlAdaptor,
    insertUrl: "Home/Insert",
    removeUrl: "Home/Delete",
    updateUrl: "Home/Update",
    url: "Home/DataSource",
});
return <TreeGridComponent dataSource={dataManager} treeColumnIndex={1} idMapping= 'TaskID'
parentIdMapping='ParentValue' hasChildMapping='isParent' expandStateMapping='IsExpanded' loadChildOnDemand='true' height='400' enableVirtualization={true} editSettings={editOptions} toolbar={toolbarOptions} allowFiltering={true} allowSorting={true} pageSettings={pageSettings}>
    <ColumnsDirective>
        <ColumnDirective field='TaskID' headerText='Task ID' width='90' textAlign='Right' isPrimaryKey={true}/>
        <ColumnDirective field='TaskName' headerText='Task Name' width='180'/>
        <ColumnDirective field='Duration' headerText='Duration' width='80' textAlign='Right' />
    </ColumnsDirective>
    <Inject services={[Edit, VirtualScroll, Sort, Filter, Toolbar]} />
</TreeGridComponent>
};
export default App;

The following code example describes handling of child records at server end.

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public ActionResult loadChildOndemand()
{
TreeData.tree = new List<TreeData>();
return View();
}
public ActionResult UrlDatasource(DataManagerRequest dm)
{
List<TreeData> data = new List<TreeData>();
data = TreeData.GetTree();
DataOperations operation = new DataOperations();
IEnumerable<TreeData> DataSource = data;
if (dm.Expand != null && dm.Expand[0] == "CollapsingAction") // setting the ExpandStateMapping property whether is true or false
{
    var val = TreeData.GetTree().Where(ds => ds.TaskID == int.Parse(dm.Expand[1])).FirstOrDefault();
    val.IsExpanded = false;
}
else if (dm.Expand != null && dm.Expand[0] == "ExpandingAction")
{
    var val = TreeData.GetTree().Where(ds => ds.TaskID == int.Parse(dm.Expand[1])).FirstOrDefault();
    val.IsExpanded = true;
}
if (!(dm.Where != null && dm.Where.Count > 1))
{
    data = data.Where(p => p.ParentValue == null).ToList();
}
DataSource = data;
if (dm.Search != null && dm.Search.Count > 0) // Searching
{
    DataSource = operation.PerformSearching(DataSource, dm.Search);
}
if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // Sorting
{
    DataSource = operation.PerformSorting(DataSource, dm.Sorted);
}
if (dm.Where != null && dm.Where.Count > 1) //filtering
{
    DataSource = operation.PerformFiltering(DataSource, dm.Where, "and");
}
data = new List<TreeData>();
foreach (var rec in DataSource)
{
    data.Add(rec as TreeData);
}
var GroupData = TreeData.GetTree().ToList().GroupBy(rec => rec.ParentValue)
                    .Where(g => g.Key != null).ToDictionary(g => g.Key?.ToString(), g => g.ToList());
foreach (var Record in data.ToList())
{
    if (GroupData.ContainsKey(Record.TaskID.ToString()))
    {
        var ChildGroup = GroupData[Record.TaskID.ToString()];
        if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // Sorting the child records
        {
            IEnumerable ChildSort = ChildGroup;
            ChildSort = operation.PerformSorting(ChildSort, dm.Sorted);
            ChildGroup = new List<TreeData>();
            foreach (var rec in ChildSort)
            {
                ChildGroup.Add(rec as TreeData);
            }
        }
        if (dm.Search != null && dm.Search.Count > 0) // Searching the child records
        {
            IEnumerable ChildSearch = ChildGroup;
            ChildSearch = operation.PerformSearching(ChildSearch, dm.Search);
            ChildGroup = new List<TreeData>();
            foreach (var rec in ChildSearch)
            {
                ChildGroup.Add(rec as TreeData);
            }
        }
        if (ChildGroup?.Count > 0)
            AppendChildren(dm, ChildGroup, Record, GroupData, data);
    }
}
DataSource = data;
if (dm.Expand != null && dm.Expand[0] == "CollapsingAction") // setting the skip index based on collapsed parent
{
    string IdMapping = "TaskID";
    List<WhereFilter> CollapseFilter = new List<WhereFilter>();
    CollapseFilter.Add(new WhereFilter() { Field = IdMapping, value = dm.Where[0].value, Operator = dm.Where[0].Operator });
    var CollapsedParentRecord = operation.PerformFiltering(DataSource, CollapseFilter, "and");
    var index = data.Cast<object>().ToList().IndexOf(CollapsedParentRecord.Cast<object>().ToList()[0]);
    dm.Skip = index;
}
else if (dm.Expand != null && dm.Expand[0] == "ExpandingAction") // setting the skip index based on expanded parent
{
    string IdMapping = "TaskID";
    List<WhereFilter> ExpandFilter = new List<WhereFilter>();
    ExpandFilter.Add(new WhereFilter() { Field = IdMapping, value = dm.Where[0].value, Operator = dm.Where[0].Operator });
    var ExpandedParentRecord = operation.PerformFiltering(DataSource, ExpandFilter, "and");
    var index = data.Cast<object>().ToList().IndexOf(ExpandedParentRecord.Cast<object>().ToList()[0]);
    dm.Skip = index;
}
int count = data.Count;
DataSource = data;
if (dm.Skip != 0)
{
    DataSource = operation.PerformSkip(DataSource, dm.Skip);   //Paging
}
if (dm.Take != 0)
{
    DataSource = operation.PerformTake(DataSource, dm.Take);
}
return dm.RequiresCounts ? Json(new { result = DataSource, count = count }) : Json(DataSource);

}

private void AppendChildren(DataManagerRequest dm, List<TreeData> ChildRecords, TreeData ParentValue, Dictionary<string, List<TreeData>> GroupData, List<TreeData> data) // Getting child records for the respective parent
{
string TaskId = ParentValue.TaskID.ToString();
var index = data.IndexOf(ParentValue);
DataOperations operation = new DataOperations();
foreach (var Child in ChildRecords)
{
    if (ParentValue.IsExpanded)
    {
        string ParentId = Child.ParentValue.ToString();
        if (TaskId == ParentId)
        {
            ((IList)data).Insert(++index, Child);
            if (GroupData.ContainsKey(Child.TaskID.ToString()))
            {
                var DeepChildRecords = GroupData[Child.TaskID.ToString()];
                if (DeepChildRecords?.Count > 0)
                {
                    if (dm.Sorted != null && dm.Sorted.Count > 0 && dm.Sorted[0].Name != null) // sorting the child records
                    {
                        IEnumerable ChildSort = DeepChildRecords;
                        ChildSort = operation.PerformSorting(ChildSort, dm.Sorted);
                        DeepChildRecords = new List<TreeData>();
                        foreach (var rec in ChildSort)
                        {
                            DeepChildRecords.Add(rec as TreeData);
                        }
                    }
                    if (dm.Search != null && dm.Search.Count > 0) // searching the child records
                    {
                        IEnumerable ChildSearch = DeepChildRecords;
                        ChildSearch = operation.PerformSearching(ChildSearch, dm.Search);
                        DeepChildRecords = new List<TreeData>();
                        foreach (var rec in ChildSearch)
                        {
                            DeepChildRecords.Add(rec as TreeData);
                        }
                    }
                    AppendChildren(dm, DeepChildRecords, Child, GroupData, data);
                    if (Child.IsExpanded)
                    {
                        index += DeepChildRecords.Count;
                    }
                }
            }
        }
    }
}

}

public ActionResult Update(CRUDModel<TreeData> value)
{
List<TreeData> data = new List<TreeData>();
data = TreeData.GetTree();
var val = data.Where(ds => ds.TaskID == value.Value.TaskID).FirstOrDefault();
val.TaskName = value.Value.TaskName;
val.Duration = value.Value.Duration;
return Json(val);
}

public ActionResult Insert(CRUDModel<TreeData> value)
{
var c = 0;
for (; c < TreeData.GetTree().Count; c++)
{
    if (TreeData.GetTree()[c].TaskID == value.RelationalKey)
    {
        if (TreeData.GetTree()[c].isParent == null)
        {
            TreeData.GetTree()[c].isParent = true;
        }
        break;
    }
}
c += FindChildRecords(value.RelationalKey);
TreeData.GetTree().Insert(c + 1, value.Value);

return Json(value.Value);
}

public int FindChildRecords(int? id)
{
var count = 0;
for (var i = 0; i < TreeData.GetTree().Count; i++)
{
    if (TreeData.GetTree()[i].ParentValue == id)
    {
        count++;
        count += FindChildRecords(TreeData.GetTree()[i].TaskID);
    }
}
return count;
}

public object Delete(CRUDModel<TreeData> value)
{
if (value.deleted != null)
{
    for (var i = 0; i < value.deleted.Count; i++)
    {
        TreeData.GetTree().Remove(TreeData.GetTree().Where(ds => ds.TaskID == value.deleted[i].TaskID).FirstOrDefault());
    }
}
else
{
    TreeData.GetTree().Remove(TreeData.GetTree().Where(or => or.TaskID == int.Parse(value.Key.ToString())).FirstOrDefault());
}
return Json(value);
}

public class CRUDModel<T> where T : class
{

public TreeData Value;
public int Key { get; set; }
public int RelationalKey { get; set; }
public List<T> added { get; set; }
public List<T> changed { get; set; }
public List<T> deleted { get; set; }
}

public class TreeData
{
public static List<TreeData> tree = new List<TreeData>();
[System.ComponentModel.DataAnnotations.Key]
public int TaskID { get; set; }
public string TaskName { get; set; }
public int Duration { get; set; }
public int? ParentValue { get; set; }
public bool? isParent { get; set; }
public bool IsExpanded { get; set; }
public TreeData() { }
public static List<TreeData> GetTree()
{
    if (tree.Count == 0)
    {
        int root = 0;
        for (var t = 1; t <= 1500; t++)
        {
            Random ran = new Random();
            string math = (ran.Next() % 3) == 0 ? "High" : (ran.Next() % 2) == 0 ? "Release Breaker" : "Critical";
            string progr = (ran.Next() % 3) == 0 ? "Started" : (ran.Next() % 2) == 0 ? "Open" : "In Progress";
            root++;
            int rootItem = root;
            tree.Add(new TreeData() { TaskID = rootItem, TaskName = "Parent task " + rootItem.ToString(), isParent = true, IsExpanded = true, ParentValue = null, Duration = ran.Next(1, 50) });
            int parent = root;
            for (var d = 0; d < 1; d++)
            {
                root++;
                string value = ((parent + 1) % 3 == 0) ? "Low" : "Critical";
                int par = parent + 1;
                progr = (ran.Next() % 3) == 0 ? "In Progress" : (ran.Next() % 2) == 0 ? "Open" : "Validated";
                int iD = root;
                tree.Add(new TreeData() { TaskID = iD, TaskName = "Child task " + iD.ToString(), isParent = true, IsExpanded = true, ParentValue = rootItem, Duration = ran.Next(1, 50) });
                int subparent = root;
                for (var c = 0; c < 6; c++)
                {
                    root++;
                    string val = ((subparent + c + 1) % 3 == 0) ? "Low" : "Critical";
                    int subchild = subparent + c + 1;
                    string progress = (ran.Next() % 3) == 0 ? "In Progress" : (ran.Next() % 2) == 0 ? "Open" : "Validated";
                    int childID = root ;
                    tree.Add(new TreeData() { TaskID = childID, TaskName = "sub Child task " + childID.ToString(), ParentValue = subparent, Duration = ran.Next(1, 50) });
                }
            }
        }
    }
    return tree;
}
}