Okay, I'll answer my own question. I found that the dataSource argument of the method PerformSelect (IEnumerable dataSource, List <string> select) does not have to be the same type as the data type in the grid. It is only important that the names of the columns for displaying the aggregates coincide with the names of the dataSource columns of the grid. At the same time, the option with an grouping by constant (in this case it is "any") and using anonymous type is quite functional:
HomeController.cs:
...
public IActionResult UrlDatasource([FromBody]DataManagerRequest dm)
{
...
IEnumerable aggdata = DataSource.Cast<OrdersDetails>()
.GroupBy(e => "any")
.Select(e => new
{
CustomerID = e.Select(o => o.CustomerID).Distinct().Count(),
ShipCity = e.Count(),
Freight = e.Average(o => o.Freight),
});
var aggregate =
dm.Aggregates != null ? operation.PerformSelect(aggdata, dm.Aggregates.Select(e => e.Field).ToList()) : null;
...
Index.cshtml:
...
<e-aggregate-columns>
<e-aggregate-column field="CustomerID" type="Sum" footerTemplate="Cust Count: ${Sum}"></e-aggregate-column>
<e-aggregate-column field="ShipCity" type="Sum" footerTemplate="Count: ${Sum}"></e-aggregate-column>
<e-aggregate-column field="Freight" type="Sum" footerTemplate="Avg: ${Sum}" format="C"></e-aggregate-column>
</e-aggregate-columns>
...
With this method, we will always receive from the server only one record with totals (therefore, e-aggregate-column type = "Sum" in all columns with aggregates) and correctly calculates the aggregates when the filter changes:
As a result, we have the following:
Currently, I still use this method until a better solution appears. The only flaw that I found at the moment is that when exporting to Excel, instead of these calculated totals, some other incorrect ones are sent:
If I'm wrong in something, you can correct me.
