Error: System.InvalidOperationException: No generic method 'Sum' on type 'System.Linq.Enumerable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic. 
   at System.Linq.Expressions.Expression.FindMethod(Type type, String methodName, Type[] typeArgs, Expression[] args, BindingFlags flags)
   at System.Linq.Expressions.Expression.Call(Type type, String methodName, Type[] typeArguments, Expression[] arguments)
   at Telerik.DataSource.Expressions.EnumerableSelectorAggregateFunctionExpressionBuilder.CreateMethodCallExpression(LambdaExpression memberSelectorExpression)
   at Telerik.DataSource.Expressions.EnumerableSelectorAggregateFunctionExpressionBuilder.CreateAggregateExpression()
   at Telerik.DataSource.EnumerableSelectorAggregateFunction.CreateAggregateExpression(Expression enumerableExpression, Boolean liftMemberAccessToNull)
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilder.<ProjectionPropertyValueExpressions>b__39_0(AggregateFunction f)
   at System.Linq.Enumerable.SelectIListIterator`2.ToList()
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilder.CreateProjectionInitExpression()
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilder.CreateAggregateFunctionsProjectionMemberBinding()
   at Telerik.DataSource.Expressions.QueryableAggregatesExpressionBuilder.CreateMemberBindings()+MoveNext()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at System.Dynamic.Utils.CollectionExtensions.ToReadOnly[T](IEnumerable`1 enumerable)
   at System.Linq.Expressions.Expression.MemberInit(NewExpression newExpression, IEnumerable`1 bindings)
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilder.CreateSelectBodyExpression()
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilder.CreateSelectExpression()
   at Telerik.DataSource.Expressions.GroupDescriptorExpressionBuilderBase.CreateQuery()
   at Telerik.DataSource.Extensions.QueryableExtensions.Aggregate(IQueryable source, IEnumerable`1 aggregateFunctions)
   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.ToDataSourceResult(IEnumerable enumerable, DataSourceRequest request)
   at Telerik.Blazor.Data.TelerikDataSourceBase.ProcessData(IEnumerable data)
   at Telerik.Blazor.Components.Common.DataBoundComponent`1.ProcessDataInternal()
   at Telerik.Blazor.Components.Common.DataBoundComponent`1.ProcessDataAsync()
   at Telerik.Blazor.Components.TelerikGrid`1.DataBoundProcessData()
   at Telerik.Blazor.Components.TelerikGrid`1.ProcessDataAsync()
   at Telerik.Blazor.Components.TelerikGrid`1.ApplyFiltersAsync()
   at Telerik.Blazor.Components.TelerikGrid`1.OnFilterChange(FilterDescriptorBase filter)
   at Telerik.Blazor.Components.Common.Filters.TelerikFilterHeader`1.Filter(FilterDescriptor filterDescriptor)
   at Telerik.Blazor.Components.Common.Filters.TelerikFilterHeader`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.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContext.ExecuteBackground(WorkItem item)

<TelerikGrid Data="listOfFoos" SelectionMode="GridSelectionMode.Multiple">
    <GridColumns>
        <GridCheckboxColumn SelectAll="true" SelectAllMode="GridSelectAllMode.All"  />
        <GridColumn Field="@nameof(Foo.Name)" Title="Name" />
    </GridColumns>
</TelerikGrid>

public class Foo {
    public string Name { get; set; }
}
public List<Foo> listOfFoos = [ new Foo{Name="First"}, new Foo{Name="Second"}, new Foo{Name="Third"} ];
   

@using Telerik.DataSource
@using Telerik.DataSource.Extensions

<TelerikGrid @ref="@GridRef"
             OnRead="@OnGridRead"
             TItem="@Product"
             Pageable="true">
    <GridAggregates>
        <GridAggregate Field="@nameof(Product.Name)" Aggregate="@GridAggregateType.Count" FieldType="@(typeof(System.String))" />
    </GridAggregates>
    <GridColumns>
        <GridColumn Field="@nameof(Product.Name)" Title="Product Name">
            <FooterTemplate>
                @context.Count
            </FooterTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Product.Price)" />
        <GridColumn Field="@nameof(Product.ReleaseDate)" Title="Release Date" />
        <GridColumn Field="@nameof(Product.Active)" />
    </GridColumns>
</TelerikGrid>

@code {
    TelerikGrid<Product> GridRef { get; set; }
    List<Product> GridData { get; set; }

    bool ShouldBindGrid { get; set; }

    async Task OnGridRead(GridReadEventArgs args)
    {
        if (!ShouldBindGrid)
        {
            return;
        }

        await Task.Delay(200); // simulate network delay

        DataSourceResult result = GridData.ToDataSourceResult(args.Request);

        args.Data = result.Data;
        args.Total = result.Total;
        args.AggregateResults = result.AggregateResults;
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            // workaround for initial Grid aggregates
            ShouldBindGrid = true;
            GridRef.Rebind();
            StateHasChanged();
        }
    }

    protected override void OnInitialized()
    {
        GridData = new List<Product>();
        var rnd = new Random();

        for (int i = 1; i <= 50; i++)
        {
            GridData.Add(new Product()
            {
                Id = i,
                Name = "Product " + i.ToString(),
                Price = (decimal)rnd.Next(1, 100),
                ReleaseDate = DateTime.Now.AddDays(-rnd.Next(60, 1000)),
                Active = i % 3 == 0
            });
        }
    }

    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
        public DateTime ReleaseDate { get; set; }
        public bool Active { get; set; }
    }
}

@using System.Collections.ObjectModel
@using Telerik.FontIcons

<TelerikGrid Data="@Cards"
             Height="800px"
             FilterMode="GridFilterMode.FilterRow"
             EditMode="GridEditMode.Inline"
             OnCreate="NewCard"
             OnUpdate="UpdateCard"
             OnDelete="DeleteCard"
             ConfirmDelete="true"
             @ref="@GridReference">
    <GridToolBarTemplate>
        <GridCommandButton Command="Add" Icon="@FontIcon.Plus">New</GridCommandButton>
    </GridToolBarTemplate>
    <GridColumns>
        <GridColumn Field="@nameof(AdminCard.SerialNumber)" Title="Serial number" />
        <GridColumn Field="@nameof(AdminCard.DisplayNumber)" Title="Display number" />
        <GridColumn Field="@nameof(AdminCard.Name)" />
        <GridCommandColumn Width="140px">
            <GridCommandButton Command="Save" Icon="@FontIcon.Save" ShowInEdit="true" />
            <GridCommandButton Command="Edit" Icon="@FontIcon.Pencil" />
            <GridCommandButton Command="Delete" Icon="@FontIcon.Trash" />
            <GridCommandButton Command="Cancel" Icon="@FontIcon.Cancel" ShowInEdit="true" />
        </GridCommandColumn>
    </GridColumns>
</TelerikGrid>

@code {
    TelerikGrid<AdminCard> GridReference { get; set; }

    public ObservableCollection<AdminCard> Cards { get; set; } = new();

    protected override async Task OnInitializedAsync() =>
      Cards = new ObservableCollection<AdminCard>{
        new AdminCard{SerialNumber="123", DisplayNumber="1234 1234", Name="Jim"}
                      };

    private async Task NewCard(GridCommandEventArgs args)
    {
        AdminCard card = (AdminCard)args.Item;
        Cards.Add(card);

        //apply this after saving the new record to the database
        var gridState = GridReference.GetState();
        gridState.InsertedItem = null;
        gridState.OriginalEditItem = null;
        await GridReference.SetStateAsync(gridState);
    }

    private async Task UpdateCard(GridCommandEventArgs args)
    {
        AdminCard fromGrid = (AdminCard)args.Item;
        AdminCard existing = Cards.Single(c => c.Id == fromGrid.Id);
        existing.SerialNumber = fromGrid.SerialNumber;
        existing.DisplayNumber = fromGrid.DisplayNumber;
        existing.Name = fromGrid.Name;
    }

    private async Task DeleteCard(GridCommandEventArgs args)
    {
        AdminCard card = (AdminCard)args.Item;
        Cards.Remove(card);
    }

    public class AdminCard
    {
        public string Id { get; set; } = Guid.NewGuid().ToString();
        public string SerialNumber { get; set; } = "";
        public string DisplayNumber { get; set; } = "";
        public string Name { get; set; } = "";
    }
}

@using Telerik.DataSource
@using Telerik.DataSource.Extensions
 
<TelerikGrid TItem="@Employee"
             OnRead="@OnReadHandler"
             Pageable="true"
             FilterMode="@GridFilterMode.FilterMenu"
             FilterMenuType="@FilterMenuType.CheckBoxList"
             ShowColumnMenu="true"
             Height="400px">
    <GridColumns>
        <GridColumn Field="@(nameof(Employee.EmployeeId))" Filterable="false" />
        <GridColumn Field="@nameof(Employee.Name)">
            <FilterMenuTemplate Context="context">
                <TelerikCheckBoxListFilter Data="@NameOptions"
                                           Field="@(nameof(NameFilterOption.Name))"
                                           @bind-FilterDescriptor="@context.FilterDescriptor">
                </TelerikCheckBoxListFilter>
            </FilterMenuTemplate>
            <FilterMenuButtonsTemplate Context="filterContext">
                <TelerikButton OnClick="@( async () => await ApplyFilterAsync(filterContext) )"
                               ThemeColor="primary">Filter</TelerikButton>
                <TelerikButton OnClick="@( async () => await ClearFilterAsync(filterContext) )">Clear</TelerikButton>
            </FilterMenuButtonsTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Employee.Team)" Title="Team">
            <FilterMenuTemplate Context="context">
                <TelerikCheckBoxListFilter Data="@TeamsList"
                                           Field="@(nameof(TeamNameFilterOption.Team))"
                                           @bind-FilterDescriptor="@context.FilterDescriptor">
                </TelerikCheckBoxListFilter>
            </FilterMenuTemplate>
        </GridColumn>
        <GridColumn Field="@nameof(Employee.IsOnLeave)" Title="On Vacation" />
    </GridColumns>
</TelerikGrid>

@code {
    List<Employee> AllGridData { get; set; }

    #region custom-filter-data
    List<TeamNameFilterOption> TeamsList { get; set; }
    List<NameFilterOption> NameOptions { get; set; }

    private async Task ApplyFilterAsync(FilterMenuTemplateContext filterContext)
    {
        var hasFilters = filterContext.FilterDescriptor.FilterDescriptors.OfType<FilterDescriptor>().Any(x => !string.IsNullOrEmpty(x.Value.ToString()));

        if (hasFilters)
        {
            await filterContext.FilterAsync();
        }
        else
        {
            await filterContext.ClearFilterAsync();
        }
    }

    private async Task ClearFilterAsync(FilterMenuTemplateContext filterContext)
    {
        await filterContext.ClearFilterAsync();
    }

    //obtain filter lists data from the data source to show all options
    async Task GetTeamOptions()
    {
        if (TeamsList == null) // sample of caching since we always want all distinct options,
                               //but we don't want to make unnecessary requests
        {
            TeamsList = await GetNamesFromService();
        }
    }

    async Task<List<TeamNameFilterOption>> GetNamesFromService()
    {
        await Task.Delay(500);// simulate a real service delay

        // this is just one example of getting distinct values from the full data source
        // in a real case you'd probably call your data service here instead
        // or apply further logic (such as tie the returned data to the data the grid will have according to your business logic)
        List<TeamNameFilterOption> data = AllGridData.OrderBy(z => z.Team).Select(z => z.Team).
            Distinct().Select(t => new TeamNameFilterOption { Team = t }).ToList();

        return await Task.FromResult(data);
    }

    async Task GetNameOptions()
    {
        if (NameOptions == null)
        {
            NameOptions = await GetNameOptionsFromService();
        }
    }

    async Task<List<NameFilterOption>> GetNameOptionsFromService()
    {
        await Task.Delay(500);// simulate a real service delay

        List<NameFilterOption> data = AllGridData.OrderBy(z => z.Name).Select(z => z.Name).
            Distinct().Select(n => new NameFilterOption { Name = n }).ToList();

        return await Task.FromResult(data);
    }
    #endregion custom-filter-data

    async Task OnReadHandler(GridReadEventArgs args)
    {
        //typical data retrieval for the grid
        var filteredData = await AllGridData.ToDataSourceResultAsync(args.Request);
        args.Data = filteredData.Data as IEnumerable<Employee>;
        args.Total = filteredData.Total;
    }

    protected override async Task OnInitializedAsync()
    {
        AllGridData = new List<Employee>();
        var rand = new Random();
        for (int i = 1; i <= 15; i++)
        {
            AllGridData.Add(new Employee()
            {
                EmployeeId = i,
                Name = "Employee " + i.ToString(),
                Team = "Team " + i % 3,
                IsOnLeave = i % 2 == 0
            });
        }

        await GetTeamOptions();
        await GetNameOptions();
    }

    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string Team { get; set; }
        public bool IsOnLeave { get; set; }
    }

    // in this sample we use simplified models to fetch less data from the service
    // instead of using the full Employee model that has many fields we do not need for the filters

    public class TeamNameFilterOption
    {
        public string Team { get; set; }
    }

    public class NameFilterOption
    {
        public string Name { get; set; }
    }
}