I'm using the self-referencing hierarchy DataGrid (I love it). At this point, there are three levels of data; Root Level, Second Level, and Third Level. I've set the ExpandMode to DataGridExpandMode.Single and included an empty RowExpand method (I saw that as a possible solution in another post). I have also set the AllowVirtualization to false (I saw that as a possible solution in a different post) The already expanded level(s) do not collapse when a new level is expanded. In your example here there is only a single root and a single second level so it doesn't demonstrate that the single expand mode works with the self-referencing hierarchy even though the example code does have the ExpandMode set to DataGridExpandMode.Single. Is that functionality included in the self-referencing hierarchy DataGrid? Below is the setup for me DataGrid. I'll include a screenshot of the actual grid with some of the rows expanded. I was expecting (hoping?) that expanding a new level would collapse all other open levels except for the last selected level.
<RadzenDataGrid @ref="_dataGrid" AllowAlternatingRows="true" Style="max-height: 65vh;"
ExpandMode="DataGridExpandMode.Single" Data="@_groupAccessItems" TItem="GroupAccessItem"
AllowVirtualization="false" RowRender="@RowRender" LoadChildData="@LoadChildData"
CellRender="@CellRender" IsLoading="@_isLoading" RowExpand="@RowExpand" >
