(accidentally posted before to complete)

   public string Cognome { get => this.Patient.Cognome; }

than the EF method:
  public async Task<IEnumerable<Card>> GetCards(DataSourceRequest request)
        {
            using (Context Db = new Context())
            {
                var list = from x in Db.Card
                        select x;

                var result = await list.ToDataSourceResultAsync(request);
                return result.Data as IEnumerable<Card>;
            }
        }

if I filter the Numero property (string) all works fine.

If I try to filter the Cognome property (string too) the eccor occurs.

UPDATE:

Sorry, It's no Telerik fault.

EF Core linq query fails translating a condition on a partial readonly property of the class.

something like this:

 var list = from x in Db.Card
                        where x.Cognome.Contains("p")
                        select x;
give the error I mentioned before.
Thanks anyway

UPDATE 2:

After further investigation I read about breaking changes in EF Core 3.0 preview 4 that disallow client-evaluation of query that cannot be propertly translate in SQL. For those interested read here .

Then in case of computed properties (as Telerik Blazor Knowledge Base suggests here Bind to navigation properties in complex objects and as I have done in the code above) it needs to use one of these solution mentioned here. 

But using Templates I should avoid the client-eval problem, so I change the following code:

 <GridColumn Field="@(nameof(Card.Patient.Cognome))" Title="Nome" Groupable="false">
       <Template>
        @((context as Card).Patient.Cognome)
       </Template>
 </GridColumn>

First of all, If I omit Field="@(nameof(Card.Patient.Cognome))" the app hang with this error:
System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at Telerik.Blazor.Components.Grid.Extensions.ColumnExtensions.GroupTitles(IEnumerable`1 columns)
   at Telerik.Blazor.Components.TelerikGrid`1.<BuildRenderTree>b__0_1(RenderTreeBuilder __builder2)
   at Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddContent(Int32 sequence, RenderFragment fragment)
   at Microsoft.AspNetCore.Components.CascadingValue`1.Render(RenderTreeBuilder builder)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Microsoft.AspNetCore.Routing.EndpointMiddleware: Information: Executed endpoint '/_blazor'
Microsoft.AspNetCore.Hosting.Diagnostics: Information: Request finished in 9533.2773ms 101 

Otherwise, If I try to filter the field (with FilterRow option) I get another error:

System.ArgumentNullException: Value cannot be null. (Parameter 'conversionType')
   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   at System.Convert.ChangeType(Object value, Type conversionType)
   at Telerik.Blazor.Components.Grid.GridFilterHeaderBase`1.OnValueChanged(Object newValue)
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__139_0(Object state)
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.ExecuteSynchronously(TaskCompletionSource`1 completion, SendOrPostCallback d, Object state)
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.<>c.<.cctor>b__23_0(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.ExecuteBackground(WorkItem item)
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Microsoft.AspNetCore.Routing.EndpointMiddleware: Information: Executed endpoint '/_blazor'
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Microsoft.AspNetCore.Hosting.Diagnostics: Information: Request finished in 5296.0234ms 101 
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll


If I try to filter the field (with FilterMenu option) I get again another different error:
System.ArgumentException: Invalid property or field - 'Nome' for type: Card
   at Telerik.DataSource.Expressions.MemberAccessTokenExtensions.CreateMemberAccessExpression(IMemberAccessToken token, Expression instance)
   at Telerik.DataSource.Expressions.ExpressionFactory.MakeMemberAccess(Expression instance, String memberName)
   at Telerik.DataSource.Expressions.ExpressionFactory.MakeMemberAccess(Expression instance, String memberName, Boolean liftMemberAccessToNull)
   at Telerik.DataSource.Expressions.PropertyAccessExpressionBuilder.CreateMemberAccessExpression()
   at Telerik.DataSource.Expressions.FilterDescriptorExpressionBuilder.CreateMemberExpression()
   at Telerik.DataSource.Expressions.FilterDescriptorExpressionBuilder.CreateBodyExpression()
   at Telerik.DataSource.FilterDescriptor.CreateFilterExpression(ParameterExpression parameterExpression)
   at Telerik.DataSource.FilterDescriptorBase.CreateFilterExpression(Expression instance)
   at Telerik.DataSource.Expressions.FilterDescriptorCollectionExpressionBuilder.CreateBodyExpression()
   at Telerik.DataSource.CompositeFilterDescriptor.CreateFilterExpression(ParameterExpression parameterExpression)
   at Telerik.DataSource.FilterDescriptorBase.CreateFilterExpression(Expression instance)
   at Telerik.DataSource.Expressions.FilterDescriptorCollectionExpressionBuilder.CreateBodyExpression()
   at Telerik.DataSource.Expressions.FilterExpressionBuilder.CreateFilterExpression()
   at Telerik.DataSource.Extensions.QueryableExtensions.Where(IQueryable source, IEnumerable`1 filterDescriptors)
   at Telerik.DataSource.Extensions.QueryableExtensions.CreateDataSourceResult[TModel,TResult](IQueryable queryable, DataSourceRequest request, Func`2 selector)
   at Telerik.DataSource.Extensions.QueryableExtensions.ToDataSourceResult(IQueryable queryable, DataSourceRequest request)
   at Telerik.DataSource.Extensions.QueryableExtensions.<>c__DisplayClass3_0.<ToDataSourceResultAsync>b__0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.<>c.<.cctor>b__274_0(Object obj)
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location where exception was thrown ---
   at Bipoint.Data.Model.BipointService.GetCards_Inseriti_PN(DataSourceRequest request) in C:\Users\francesco\Documents\myprojects\2Next\Projects\Bipoint\prove\BipointB\Data\Model\BipointService.cs:line 31
   at Bipoint.Pages.Pn.ReadItems(GridReadEventArgs args) in C:\Users\francesco\Documents\myprojects\2Next\Projects\Bipoint\prove\BipointB\Pages\Pn.razor:line 62
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Telerik.Blazor.Components.TelerikGridBase`1.ProcessData()
   at Telerik.Blazor.Components.TelerikGridBase`1.OnFilterChange(FilterDescriptorBase filter)
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Telerik.Blazor.Components.Common.Filters.FilterMenu.TelerikFilterMenuBase.Filter()
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(Task taskToHandle)
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Microsoft.AspNetCore.Routing.EndpointMiddleware: Information: Executed endpoint '/_blazor'
Eccezione generata: 'System.ObjectDisposedException' in Microsoft.AspNetCore.Components.dll
Eccezione generata: 'System.ObjectDisposedException' in Microsoft.AspNetCore.Components.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll
Eccezione generata: 'System.InvalidOperationException' in Microsoft.AspNetCore.Components.Server.dll
Microsoft.AspNetCore.Hosting.Diagnostics: Information: Request finished in 25149.4359ms 101 
Eccezione generata: 'System.InvalidOperationException' in Microsoft.JSInterop.dll

I'm sorry for the long post and a bit confused, but I hope can help you to improve your product.
Thanks

Hi,

As the KB article you found states - at the moment only flat data models are supported. Nesting objects causes exceptions.

We had a spike of similar requests recently, so I have reopened the investigation into the ability to support nested (complex, navigation, or whatever else you may call them) models. Here's a link for a page you can Follow: https://feedback.telerik.com/blazor/1432615-support-for-nested-complex-models.

Regards,
Marin Bratanov
Progress Telerik