为什么我的表格没有根据 MVC 中的下拉菜单显示我想要的结果？

我目前正在创建一个 MVC 应用程序，我想显示一个部分页面，其中包含基于所选下拉列表的汽车列表。我还希望我的应用程序在不需要选择所有下拉菜单的情况下进行搜索。有人建议我使用 if 语句来完成此操作，但我不确定我是否正确执行此操作。目前我无法通过单个下拉列表或 1 个下拉列表 +“可用”下拉列表的任意组合进行搜索。我没有收到任何错误，但没有显示任何结果。

这是我的看法

@model IgnitionHub2._0.Models.Car
@{
    ViewBag.Title = "Car Search Page";
}


<h2>Cars</h2>
<p>
    @Html.ActionLink("Create New", "Create")
</p>
<div class="center-div">
    <div class="form-inline">
        @Html.DropDownListFor(model => model.CarLotID, new SelectList(Model.CarLotList, "CarLotID", "LotName"), "Select Car Lot", new { @class = "form-control" })
        @Html.DropDownListFor(model => model.Model.MakeID, new SelectList(Model.MakeList, "MakeID", "Name"), "Select Make", new { @class = "form-control" })
        @Html.DropDownListFor(model => model.ModelID, new SelectList(Model.ModelList, "ModelID", "Name"), "Select Model", new { @id = "ModelID", @class = "form-control" })
        @Html.DropDownListFor(model => model.Available, new[] { new SelectListItem { Text = "Yes", Value = "true" }, new SelectListItem { Text = "No", Value = "false" } }, "Available", new { @id = "Available", @class = "form-control" })
        <button id="search">Search</button>
    </div>
</div>
<div id="searchResults">
    @{Html.RenderPartial("_Index", Model.CarList);}
</div>
@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
    <script src="~/Scripts/jquery-3.4.1.min.js"></script>
    <script src="~/Scripts/jquery.validate.min.js"></script>
    <script src="~/Scripts/jquery.validate.unobtrusive.min.js"></script>

    <script type="text/javascript">
    $(document).ready(
        function () {
        var makeUrl = '@Url.Action("GetCarDetails")';
        var models = $('#ModelID')
        $('#Model_MakeID').change(function () {
            models.empty();
                $.getJSON(makeUrl, { MakeID: $(this).val() },function(data){
                    if (!data) {
                        return;
                    }
                    models.append($('<option></option>').val('').text('Please select'));
                    $.each(data, function(index, item) {
                        models.append($('<option value=' + item.ModelID + '></option>').text(item.Name));
                    });
                });
            })
        })
        $(document).ready(function () {
         var url = '@Url.Action("DisplaySearchResults","Car")';
        $('#search').click(function () {
            var carLotID = $('#CarLotID').val();
            var makeID = $('#Model_MakeID').val();
            var modelID = $('#ModelID').val();
            var available = $('#Available').val();
            $('#searchResults').load(url + "?CarLotID=" + carLotID + "&MakeID=" + makeID + "&ModelID=" + modelID +"&Available=" + available);
        })
        })
    </script>
}

这是我的控制器

public ActionResult DisplaySearchResults(int? CarLotID, int? MakeID, int? ModelID, bool? Available)
    {
        if (CarLotID == null)
        {
            var makeModel = db.Cars.Where(c => c.Model.MakeID == MakeID && c.ModelID == ModelID && c.Available == Available).ToList();

           return PartialView("_Index", makeModel);
        }
        if (MakeID == null)
        {
            var calotModel = db.Cars.Where(c => c.CarLotID == CarLotID && c.ModelID == ModelID && c.Available == Available).ToList();
            return PartialView("_Index", calotModel);
        }
        if (ModelID == null)
        {
            var makeCarLot = db.Cars.Where(c => c.CarLotID == CarLotID && c.Model.MakeID == MakeID && c.Available == Available).ToList();
            return PartialView("_Index", makeCarLot);
        }
        if (Available == null)
        {
            var mmLot = db.Cars.Where(c => c.CarLotID == CarLotID && c.Model.MakeID == MakeID && c.ModelID==ModelID).ToList();
            return PartialView("_Index", mmLot);
        }
        if(Available == null & CarLotID == null)
        {
            var model = db.Cars.Where(c => c.Model.MakeID == MakeID && c.ModelID == ModelID).ToList();
            return PartialView("_Index", model);
        }
        if (Available == null && MakeID == null)
        {
            var model = db.Cars.Where(c => c.CarLotID == CarLotID && c.ModelID == ModelID).ToList();
            return PartialView("_Index", model);
        }
        if (Available == null && ModelID == null)
        {
            var model = db.Cars.Where(c => c.Model.MakeID == MakeID && c.CarLotID == CarLotID).ToList();
            return PartialView("_Index", model);
        }
        if (ModelID == null && CarLotID == null)
        {
            var model = db.Cars.Where(c => c.Model.MakeID == MakeID && c.Available == Available).ToList();
            return PartialView("_Index", model);
        }
        if (MakeID == null && CarLotID == null)
        {
            var model = db.Cars.Where(c => c.ModelID == ModelID && c.Available == Available).ToList();
            return PartialView("_Index", model);
        }
        if (MakeID == null && ModelID == null)
        {
            var model = db.Cars.Where(c => c.CarLotID == CarLotID && c.Available == Available).ToList();
            return PartialView("_Index", model);
        }
        if (ModelID == null && CarLotID == null && MakeID==null)
        {
            var model = db.Cars.Where(c => c.Available == Available).ToList();
            return PartialView("_Index", model);
        }
        if (ModelID == null && CarLotID == null && Available == null)
        {
            var model = db.Cars.Where(c => c.Model.MakeID == MakeID).ToList();
            return PartialView("_Index", model);
        }
        if (Available == null && CarLotID == null && MakeID == null)
        {
            var model = db.Cars.Where(c => c.ModelID == ModelID).ToList();
            return PartialView("_Index", model);
        }
        if (ModelID == null && Available == null && MakeID == null)
        {
            var model = db.Cars.Where(c => c.CarLotID == CarLotID).ToList();
            return PartialView("_Index", model);
        }
        if (ModelID == null && Available == null && MakeID == null &&CarLotID==null)
        {
            var model = db.Cars.ToList();
            return PartialView("_Index",model);
        }
        else
        {
            var model = db.Cars.Where(c => c.Model.MakeID == MakeID && c.ModelID == ModelID &&
            c.CarLotID == CarLotID && c.Available == Available).ToList();// build list based on parameter searchText
            return PartialView("_Index", model);
        }
    }
    public ActionResult _Index()
    {
        var cars = new List<Car>(db.Cars.Include(x => x.Images).ToList()); 
        return PartialView(cars);
    }

我没有包含这篇文章的部分页面，因为它没有引起任何问题，而且我不想让这篇文章更长。

请帮忙！先感谢您。