ViewBag 选择列表返回年份，使用 GroupBy 消除同一年的多个年份

Question

I am having some issues creating a viewbag selectlist. I am grabbing from a table where there are multiple records with the same date - Year. The Goal is to create a dropdown of years to select from. I think my controller is good but not sure and the view is definitely not correct.

Here is what I have:

Controller:

    public ActionResult MilesReport(long? Year)
    {
        long Years = Year ?? db.ExpenseReportsDetails.FirstOrDefault().CreatedDate.Year;
        var list = db.ExpenseReportsDetails.GroupBy(i => i.CreatedDate.Year).ToList();
        ViewBag.Year = new SelectList(list, "CreatedDate.Year", "CreatedDate.Year", Years);

        //var miles = db.ExpenseReportsDetails.Where(x => x.Miles > 0 && x.CreatedDate.Year == Year);

        return View();
    }

And here is the View:

@Html.DropDownList("Year", "--Select--")

The controller while in debug gets a count of 2 which is correct there is only 2021 and 2022.

I get this error on the view Dropdown:

DataBinding: 'System.Data.Entity.Core.Objects.ELinq.InitializerMetadata+Grouping`2[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[BestenEquipment.GeneralDTO.Entities.ExpenseReportsDetails, BestenEquipment, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' does not contain a property with the name 'CreatedDate'.

I am not sure why it says there is not a CreatedDate when there is.

Thanks for your help!

Answer 1

try this

 var list = db.ExpenseReportsDetails.Select(s=> s.CreatedDate.Year).Distinct(). ToList();
 ViewBag.Year = list.Select(i=> new SelectListItem{ Value=s.ToString(), Text = s.ToString()}.ToList();

view

 @Html.DropDownListFor(model => model.Year, @ViewBag.Year, "select", new { @class = "form-control" })

Answer 2

I did not have to use this on the above. However I did use it for another page. Below is what I found to work with the help of the answer by Serge. It did not work the way he had it but I was able to reconstruct it so it did. Here is what the solution ended up being.

 AccountingEntities acct = new AccountingEntities();
 var list = acct.Transaction.Select(s => s.TransactionDate.Year).Distinct().Select(i => new SelectListItem { Value = i.ToString(), Text = i.ToString() });
 ViewBag.Year = list.Select(x => new SelectListItem
                                 {
                                    Value = x.Text,
                                    Text = x.Text
                                 }).ToList();

Then in the View I added this:

 @Html.DropDownList("Year", " -Select- ")

This does seem redundant to me but it works, and did not work with the var list to just a .ToList . Meaning on the Viewbag.Year when putting Value = x. and Text = x. Value = x. and Text = x. It did not know what Text & Value was.