This article will describe how to filter a list of entities. I will assume you have created a new ASP.NET Core 2.2 Razor Pages project. I won't use Identity or Individual User Accounts.

This article continues a series about table functions:

• ASP.NET Core 2.2 - In Memory Entities
• ASP.NET Core 2.2 - Bootstrap 4 Tables
• ASP.NET Core 2.2 - Details Modal With JSON Entity
• ASP.NET Core 2.2 - Autocomplete Search
• ASP.NET Core 2.2 - Bootstrap 4 Pagination
• ASP.NET Core 2.2 - Filtering Entities
• ASP.NET Core 2.2 - Sorting Entities

The FREE ASP.NET Core 6.0 - Demos And Utilities Project includes a Table Functions Demo. Access to the source code is free for registered users at Manage > Assets.

I will try to add value to many great articles about filtering by using a dropdown and radio button group to select entities.

Edit Index.cshtml.cs, add the filtering properties and queries:

private readonly FoodDbContext _context;

public IndexModel(FoodDbContext context)
{
    _context = context;
}

public int Count { get; set; }

public class RadioButtonProperties
{
    public string Name { get; set; }
    public string ElementId { get; set; }
    public bool IsSelected { get; set; }
}

public List<RadioButtonProperties> ColdStoreRadioButtons { get; set; }

[Display(Name = "Store Cold")]
public string SelectedColdStoreRadio { get; set; }

[Display(Name = "Food Type")]
public FoodType SelectedFoodType { get; set; }

public IList<SelectListItem> FoodTypes { get; set; } = new List<SelectListItem>();

public IList<Food> Foods { get; set; } = new List<Food>();

public void OnGet(FoodType selectedFoodType = FoodType.All, string selectedColdStoreRadio = "All")
{
            
    SelectedFoodType = selectedFoodType;
            
    FoodTypes = new List<SelectListItem>();
    var options = Enum.GetValues(typeof(FoodType));
    foreach (var type in options)
    {
        FoodTypes.Add(new SelectListItem() { Text = type.ToString(), Value = type.ToString() });
    }

    ColdStoreRadioButtons = new List<RadioButtonProperties>()
    {
        new RadioButtonProperties() { Name = "All", ElementId = "ColdStoreRadioButtonAll" },
        new RadioButtonProperties() { Name = "Yes", ElementId = "ColdStoreRadioButtonYes" },
        new RadioButtonProperties() { Name = "No", ElementId = "ColdStoreRadioButtonNo" }
    };

    SelectedColdStoreRadio = selectedColdStoreRadio;

    var foodQuery = _context.Foods.AsQueryable();

    switch (SelectedFoodType)
    {
        case FoodType.Fruit:
            foodQuery = _context.Foods.Where(f => f.FoodType == FoodType.Fruit).AsQueryable();
            break;
        case FoodType.Vegtable:
            foodQuery = _context.Foods.Where(f => f.FoodType == FoodType.Vegtable).AsQueryable();
            break;
        case FoodType.Other:
            foodQuery = _context.Foods.Where(f => f.FoodType == FoodType.Other).AsQueryable();
            break;
        default:
            break;
    }

    switch (SelectedColdStoreRadio)
    {
        case "Yes":
            foodQuery = foodQuery.Where(f => f.ColdStore == true).AsQueryable();
            break;
        case "No":
            foodQuery = foodQuery.Where(f => f.ColdStore == false).AsQueryable();
            break;
        default:
            break;
    }

    Foods = foodQuery.ToList();

    Count = Foods.Count();

}

Edit Index.cshtml, add the dropdown and radio buttons:

<div class="row pt-1 mb-2">
    <div class="col-12 mb-1">
        <a asp-route-currentPage=""
           asp-route-selectedFoodType=""
           asp-route-selectedColdStoreRadio=""
           class="btn btn-primary">Reset</a>
        <h4 class="d-inline ml-2">
            Count = @Model.Count.ToString()
        </h4>
    </div>
</div>
<div class="row mb-2">
    <div class="col-12 col-md-4 col-lg-4">
        <h5 class="">@Html.DisplayNameFor(model => model.SelectedFoodType)</h5>
        <form class="" id="FoodTypeForm" method="get">
            <input type="hidden" asp-for="SelectedColdStoreRadio" />
            <select class="form-control mb-1" asp-for="SelectedFoodType"
                    asp-items="@Model.FoodTypes"
                    onchange="getFoodType();"></select>
        </form>
    </div>
    <div class="col-12 col-md-5 col-lg-6 mb-2">
        <h5 class="">@Html.DisplayNameFor(model => model.SelectedColdStoreRadio)</h5>
        @for (var i = 0; i < Model.ColdStoreRadioButtons.Count(); i++)
        {
            <div class="custom-control custom-radio custom-control-inline">
                <input type="radio" value="@Model.ColdStoreRadioButtons[i].Name" class="custom-control-input"
                       id="@Model.ColdStoreRadioButtons[i].ElementId" asp-for="SelectedColdStoreRadio" />
                <label class="custom-control-label" for="@Model.ColdStoreRadioButtons[i].ElementId">
                    @Model.ColdStoreRadioButtons[i].Name
                </label>
            </div>
        }
    </div>
</div>

Notice the Enum.GetValues(typeof(FoodType)).

Edit Index.cshtml, add the JavaScript:

function getFoodType() {
    document.querySelector('#FoodTypeForm').submit();
}

// After DOMContentLoaded
var coldStoreRadioButtons = document.querySelectorAll('[name="SelectedColdStoreRadio"]');
var rbl = coldStoreRadioButtons.length;
for (var rb = 0; rb < rbl; rb++) {
    coldStoreRadioButtons[rb].addEventListener('click', function (event) {
        var selectFoodType = document.querySelector('#SelectedFoodType');
        var foodType = selectFoodType.options[selectFoodType.selectedIndex].text;
        var coldStore = document.querySelector('input[name="SelectedColdStoreRadio"]:checked').value;
        location.replace('/index?currentPage=1' +
            '&selectedFoodType=' + foodType +
            '&selectedColdStoreRadio=' + coldStore);
    });
}

Build, run and test.