No generic method 'Contains' on type 'System.Linq.Enumerable'

Question

Hi,

In my Blazor Server application, I am trying to filter a data grid. I am using the Radzen library. I want to add the Blazorise library (DatePicker) in order to select multiple dates. The problem is, DatePicker needs IReadOnlyList but on the other hand, the Radzen Data filter wants IEnumerable.

I used selectedDates.AsEnumerable() but I am getting this error. How can I fix this?

System.InvalidOperationException: No generic method 'Contains' 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.

<RadzenDataFilter @ref="dataFilter" Auto="auto" Data="@_orders" TItem="ReportViewModel" ViewChanged="@(view => filteredOrders = view.ToList())"
                      FilterCaseSensitivity="FilterCaseSensitivity.CaseInsensitive">
        <Properties>
            
            <RadzenDataFilterProperty TItem="ReportViewModel" Property="OrderDateTime" Title="Order Date" FormatString="{0:d}" FilterValue="@selectedDates.AsEnumerable()" 
                                      Type="typeof(IEnumerable<DateTime?>)"
                                      FilterOperator="FilterOperator.Contains">
                <FilterTemplate>
                    <DatePicker @bind-Dates="selectedDates" TValue="DateTime?" InputMode="DateInputMode.Date" SelectionMode="DateInputSelectionMode.Multiple" 
                                DisplayFormat="dd/MM/Y" Placeholder="DD/MM/YYYY" />
                </FilterTemplate>
            </RadzenDataFilterProperty>
            
        </Properties>
    </RadzenDataFilter>

@code {
    RadzenDataFilter<ReportViewModel> dataFilter;
    IEnumerable<ReportViewModel> _orders;
    IEnumerable<ReportViewModel> filteredOrders;
    IQueryable<ReportViewModel?> query;
    IReadOnlyList<DateTime?> selectedDates = new List<DateTime?>().AsReadOnly();

Answer 1

The issue you are facing is due to the incompatibility between the Contains LINQ method and the IEnumerable<DateTime?> data type. Instead of using Contains, you can define a custom filter method for your RadzenDataFilterProperty.

First, create a custom filter method FilterByDates in your @code block:

bool FilterByDates(ReportViewModel report)
{
    if (selectedDates == null || !selectedDates.Any())
    {
        return true;
    }

    return selectedDates.Contains(report.OrderDateTime);
}

Then, modify your RadzenDataFilterProperty to use this custom filter method:

<RadzenDataFilterProperty TItem="ReportViewModel" Property="OrderDateTime" Title="Order Date" FormatString="{0:d}" FilterValue="FilterByDates"
                          Type="typeof(Func<ReportViewModel, bool>)" FilterOperator="FilterOperator.Custom">
    <FilterTemplate>
        <DatePicker @bind-Dates="selectedDates" TValue="DateTime?" InputMode="DateInputMode.Date" SelectionMode="DateInputSelectionMode.Multiple"
                    DisplayFormat="dd/MM/Y" Placeholder="DD/MM/YYYY" />
    </FilterTemplate>
</RadzenDataFilterProperty>

By using a custom filter method, you can perform filtering based on the selected dates without running into the Contains method compatibility issue.

Answer 2

This works for me;

<RadzenCard class="mb-3">
    <RadzenDataFilter @ref="dataFilter" Auto="auto" Data="@_orders" TItem="ReportViewModel" ViewChanged="@(view => filteredOrders = view.ToList())"
                      FilterCaseSensitivity="FilterCaseSensitivity.CaseInsensitive">
        <Properties>
            
            <RadzenDataFilterProperty TItem="ReportViewModel" Property="OrderDateTime" Title="Order Date" FormatString="{0:d}" 
                                      FilterValue="@filteredDates"
                                      Type="typeof(IEnumerable<DateTime>)"
                                      FilterOperator="FilterOperator.Contains">
                <FilterTemplate>
                    <DatePicker Dates="selectedDates" TValue="DateTime" InputMode="DateInputMode.Date" SelectionMode="DateInputSelectionMode.Multiple"
                                DisplayFormat="dd/MM/Y" Placeholder="DD/MM/YYYY" DatesChanged="@OnDatesChanged" />
                </FilterTemplate>
            </RadzenDataFilterProperty>
            
        </Properties>
    </RadzenDataFilter>

@code {
    RadzenDataFilter<ReportViewModel> dataFilter;
    IEnumerable<ReportViewModel> filteredOrders;
    bool auto = true;
    
    IReadOnlyList<DateTime> selectedDates = new List<DateTime>().AsReadOnly();
    IEnumerable<DateTime> filteredDates;
    
    Task OnDatesChanged(IReadOnlyList<DateTime> values)
    {
        filteredDates = values.Cast<DateTime>();
        return Task.CompletedTask;
    }
}