Load On Demand Group Data

Updated on Aug 28, 2026

The grid component lets you load the data for each individual group on demand, instead of having it always present.

In this article:

• Basics
  • Server Operations
• Examples
  • Regular Paging and Group Load On Demand
  • Virtual Scrolling, Group Load On Demand and Server Data Operations
  • Toggle Group Load Mode at Runtime
• Limitations

Basics

To enable load-on-demand for the groups, set LoadGroupsOnDemand="true" for the Grid. In this mode, the Grid behaves as usual when there is no grouping, and you can use this together with Virtual Scrolling for the rows.

Once grouping is applied (either manually by the user, or through the Grid state), the groups will now show up collapsed by default. When the user expands a group, all its rows will be requested from the data source. If you provide all the Data to the Grid, the component will perform the operations for you. For details about server operations, see below.

Each group header, each group footer and the Grid footer will count as rows for the purposes of paging. Until you expand a group, its child items are not counted and shown in the Total count for the purposes of paging.

Server Operations

When loading data on demand through the OnRead event, there can be three different kinds of requests, depending on the needed data:

• If there is no grouping, the request is as usual - no additional parameters or settings are added by the Grid.

• If there is grouping and the grid needs a list of groups, the GroupPaging parameter of its DataSourceRequest will be set to true.

  • If the currently expanded group row has subgroups, a request is sent with the GroupPaging parameter set to true, prompting that the response must include the total of items in the sub group and return a collection of groups once again, instead of a collection of models.

  • If the Grid starts with grouping set, it will make one request for the list of all groups, and will keep them in memory for paging.

• If the currently expanded group row does not have subgroups, the Filter parameter of the DataSourceRequest will contain the group value (and the values of any subgroups) for which the items are requested. The PageSize of that request is set to 0 so the Grid gets all items for that group. The OnRead event will fire every time you expand a group to get all items for that group.

While grouping is active, paging and virtual scrolling operations do not trigger OnRead, because the Grid already has all the group headers and all the items from the currently expanded groups.

Examples

This section contains the following examples:

• Regular Paging and Group Load On Demand - a basic example how to enable the feature
• Virtual Scrolling, Group Load On Demand and Server Data Operations - mimics an actual data service to implement load on demand when the user expands a group. No requests are made during scrolling. The PageSize determines the number of rendered rows, but not the number of expected rows in data requests. The example also shows how to set the initial Grid state to include grouping.

Regular Paging and Group Load On Demand

This example shows the basics of enabling the group load on demand - setting LoadGroupsOnDemand="true". Group the grid by the Team and/or Vacation columns to see the effect.

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Virtual Scrolling, Group Load On Demand and Server-side Data Operations

This example shows how you can combine the virtual row scrolling feature with loading group data on demand through a remote service (mocked by a static class in this example so you can run it easily), and how to set the initial state of the grid to have grouping by default.

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Toggle Group Load Mode at Runtime

To toggle how the Grid loads groups:

1. Obtain reference to the Grid instance with @ref.
2. Change the LoadGroupsOnDemand parameter value.
3. Rebind() the Grid.

Switch the Grid group load mode

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Limitations

• The expanded state of the groups is preserved during paging only, but not if sorting or filtering is applied.

• Since group headers and footers are treated like rows in the grid, the group headers may remain on a previous page from the data when you page the grid.

• If the group load on demand is used in combination with virtual scrolling:

  • All requirements and limitations of virtual scrolling apply.

  • Aggregates are not supported.

• When exporting only the current Grid page (AllPages="false"), the exported file will not contain child data for collapsed groups.

See Also

• Live Demo: Grid Group Load On Demand
• Blazor Grid