Load Data on Demand

The TreeList can load a remote dataset dynamically as a user expands nodes. The dataset must have a plain structure.

This feature requires client- and server-side configurations. To configure the client-side part, do the following:

Send an expanded node's ID to the server
For this, implement the CustomStore's load function. In this demo, we do it in the dataSource configuration object.
Delegate filtering to the server
Set the remoteOperations.filtering property to true.
Specify the data field that defines whether the node has children
Use the hasItemsExpr property to set this data field.

Server-side implementation is available in the ASP.NET Core and ASP.NET MVC versions of this demo under the TreeListDataController.cs tab.

NOTE

This demo uses a simple data bind technique that is useful for data display purposes only. When a user clicks a node, TreeList receives a JSON object from the server, which is based on the parentIds property value. This technique does not support the built-in data process operations in TreeList on the server.

If your project needs to process data, do one of the following instead:

Implement a custom data source. See the Custom Data Source demo.
Use the DevExtreme.AspNet.Data extension as shown in the Web API Service demo.

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Backend API

@(Html.DevExtreme().TreeList() .ID("treelist") .DataSource(new JS("treeList_dataSource")) .KeyExpr("id") .ParentIdExpr("parentId") .HasItemsExpr("hasItems") .ShowBorders(true) .RemoteOperations(r => r.Filtering(true)) .Columns(columns => { columns.Add() .DataField("name"); columns.Add() .DataField("size") .CustomizeText("treeList_size_customizeText") .Width(100); columns.Add() .DataField("createdDate") .DataType(GridColumnDataType.Date) .Width(150); columns.Add() .DataField("modifiedDate") .DataType(GridColumnDataType.Date) .Width(150); }) .RootValue("") ) <script> function treeList_size_customizeText(e) { if(e.value !== null) { return Math.ceil(e.value / 1024) + " KB"; } } var treeList_dataSource = { load: function(options) { return $.ajax({ url: "@Url.Content("~/api/TreeListData")", dataType: "json", data: { parentIds: options.parentIds.join(",") } }); } }; </script>

using Microsoft.AspNetCore.Mvc; using DevExtreme.NETCore.Demos.Models.SampleData; namespace DevExtreme.NETCore.Demos.Controllers { public class TreeListController : Controller { public ActionResult LoadDataOnDemand() { return View(); } } }

using System; using System.Linq; using System.Net.Http; using System.IO; using Microsoft.AspNetCore.Mvc; using Microsoft.AspNetCore.Hosting; namespace DevExtreme.NETCore.Demos.Controllers.ApiControllers { [Route("api/[controller]")] public class TreeListDataController : Controller { IWebHostEnvironment _webHostEnvironment; public TreeListDataController(IWebHostEnvironment webHostEnvironment) { _webHostEnvironment = webHostEnvironment; } [HttpGet] public object Get(string parentIds) { var parents = string.IsNullOrEmpty(parentIds) ? new[] { "" } : parentIds.Split(','); var rootPath = _webHostEnvironment.ContentRootPath; var childNodes = parents.SelectMany(parentId => { var parentPath = String.IsNullOrEmpty(parentId) ? rootPath : Path.Combine(rootPath, parentId); return Directory.EnumerateFileSystemEntries(parentPath); }) .Where(path => Path.GetFullPath(path).StartsWith(rootPath)) .Select(path => { var fileInfo = new FileInfo(path); var isDirectory = System.IO.File.GetAttributes(path).HasFlag(FileAttributes.Directory); var parentId = Path.GetDirectoryName(path.Substring(rootPath.Length + 1)); return new { id = Path.Combine(parentId, Path.GetFileName(path)), parentId, name = Path.GetFileName(path), modifiedDate = fileInfo.LastWriteTime, createdDate = fileInfo.CreationTime, size = isDirectory ? (long?)null : fileInfo.Length, isDirectory, hasItems = isDirectory && Directory.EnumerateFileSystemEntries(path).Count() > 0 }; }) .Where(i => i.name != "bin" && i.name != "obj" && i.name != "packages" && i.name.Length > 0 && !i.name.StartsWith(".")) .OrderByDescending(i => i.isDirectory) .ThenBy(i => i.name); return childNodes; } } }

#treelist { max-height: 440px; }