如何在 asp.net 核心 3.1 mvc 中保留所有查询字符串值？

Question

I have an asp.net core 3.1 mvc project where I have a search page (view). I am persisting search, filter and sort criteria values via Session data. This works fine, and persists data correctly, but the querystring does not contain all the information I need it to.

Values for the filters and search are selected via a form, and submit button, but sorting is selected by clicking the column headers in the search results. eg:

   <form asp-controller="Companies" asp-action="Index" method="get">
        <p>
           <label>Company Name: </label>
           <select asp-for="CompanyName" asp-items="Model.CompanyName">
                  <option value="">All</option>
           </select> 
           <input type="submit" value="Find" />
        </p>
    </form>

<table class="table">
 <thead>
   <tr>
      <th>
         <a asp-action="Index" asp-route-sortOrder="CompanyName">@Html.DisplayNameFor(model => model.CompaniesListViewModelList[0].CompanyName)</a>
      </th>
   </tr>
 </thead>
 <tbody>
     @foreach (var item in Model.CompaniesListViewModelList)
     {
         <tr>
            <td>
                @Html.DisplayFor(modelItem => item.CompanyName)
            </td>
            <td>
                <a asp-action="Edit" asp-route-id="@item.Id">Edit</a> |
                <a asp-action="Details" asp-route-id="@item.Id">Details</a> |
                <a asp-action="Delete" asp-route-id="@item.Id">Delete</a>
            </td>
         </tr>
     }
 </tbody>
</table>

If the clicks in the header to change the sort order, none of the querystring values for the filters etc appear in the querystring.

The reason I need this is so that a link can be sent to someone else.

So the question is, how do I get all the used querystring values to appear in the querystring?

Answer 1

In the Index action method, you could use ViewBag or ViewData to store the current search value (the CompanyName), then transfer it to the view page:

Then, for the sort links, you could use asp-route-{value} to add the current search value as the route parameter, and bind values via the ViewData or ViewBag. Code like this:

 <a asp-action="Index" asp-route-CompanyName="@ViewData["CurrentFilter"]" asp-route-sortOrder="@ViewData["CompanyNameSortParm"]">CompanyName</a>

The sample code as below:

Models:

public class Employee
{
    public int EmployeeId { get; set; }
    public string EmployeeName { get; set; } 
    public string CompanyName { get; set; }
     
}
public class Company
{
    public int CompanyId { get; set; }
    public string CompanyName { get; set; }
    public List<Employee> Employees { get; set; }
}
public class EmployeeVM
{
    public string CompanyName { get; set; }
    public List<Company> AllCompanies { get; set; }
    public List<Employee> Employees { get; set; }
}

Controller:

public class CompaniesController : Controller
{
    public IActionResult Index(string sortOrder, string CompanyName)
    { 
        ViewData["CompanyNameSortParm"] = String.IsNullOrEmpty(sortOrder) ? "companyname_desc" : "";
        ViewData["CurrentFilter"] = CompanyName;

        var employees = from s in repo.GetEmployees()
                       select s;
        if (!String.IsNullOrEmpty(CompanyName))
        {
            employees = employees.Where(s => s.CompanyName.Contains(CompanyName));
        }
        switch (sortOrder)
        {
            case "companyname_desc":
                employees = employees.OrderByDescending(s => s.CompanyName);
                break; 
            default:
                employees = employees.OrderBy(s => s.EmployeeId);
                break;
        }

        EmployeeVM vm = new EmployeeVM();
        vm.Employees = employees.ToList();
        vm.AllCompanies = repo.GetAllCompanies().ToList();

        return View(vm);
    }
}

Index Views:

@model netcore3.Data.EmployeeVM
 
<form asp-controller="Companies" asp-action="Index" method="get">
    <p>
        <label>Company Name: </label>
        <select asp-for="CompanyName" asp-items="@(new SelectList(Model.AllCompanies, "CompanyName","CompanyName"))">
            <option value="">All</option>
        </select>
        <input type="submit" value="Find" />
    </p>
</form>
<table class="table">
    <thead>
        <tr>
            <th>
                EmployeeName
            </th>
            <th>
                <a asp-action="Index" asp-route-CompanyName="@ViewData["CurrentFilter"]" asp-route-sortOrder="@ViewData["CompanyNameSortParm"]">CompanyName</a>
            </th>
            <th></th>
        </tr>
    </thead>
    <tbody>
        @foreach (var item in Model.Employees)
        {
            <tr>
                <td>
                    @Html.DisplayFor(modelItem => item.EmployeeName)
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.CompanyName)
                </td>
                <td>
                    <a asp-action="Edit" asp-route-id="@item.EmployeeId">Edit</a> |
                    <a asp-action="Details" asp-route-id="@item.EmployeeId">Details</a> |
                    <a asp-action="Delete" asp-route-id="@item.EmployeeId">Delete</a>
                </td>
            </tr>
        }
    </tbody>
</table>

The result like this:

Reference:

Tutorial: Add sorting, filtering, and paging - ASP.NET MVC with EF Core

Anchor Tag Helper in ASP.NET Core