Updating multiple records at once in asp.net mvc

Question

I am trying to create a website using asp.net mvc 4 and EF6 , where I want to update several lines at once. But for some reason it doesn’t work, and I get this error,

System.NullReferenceException: object reference not set to object instance

Here are my codes

controller

 [HttpPost] public ActionResult MakeDue(List<BillCheck> BillLists) { if (Session["username"] != null) { if (ModelState.IsValid) { foreach (var BillId in BillLists) { var getDue = db.BillChecks.Where(p => p.id == BillId.id).FirstOrDefault(); getDue.due = BillId.due; } db.SaveChanges(); return RedirectToAction("Success"); } else { return RedirectToAction("Failed"); } } else { return RedirectToAction("Login"); } } 

View

 @using (Html.BeginForm("MakeDue", "Home")) { @Html.ValidationSummary(true) @foreach(var item in Model.DueList) { @Html.HiddenFor(modelItem => item.id) <tr> <td>@Html.DisplayFor(modelItem => item.flat)</td> <td>@Html.DisplayFor(modelItem => item.name)</td> <td>@Html.TextBoxFor(modelItem => item.due)</td> </tr> } <input type="submit" class="btn btn-success" value="Update" /> } 

Is there something wrong in my code? How can I immediately update all inputs for due ?

Answer 1

Your first problem is that you are using the foreach , creating duplicate name attributes that will not bind to the collection, and as a result, the BillLists parameter BillLists always be an empty collection (duplicate id attributes that are invalid html will also generate it). You need to use a for loop or a custom EditorTemplate for typeof BillCheck . Using a for loop, your view should be

 using (Html.BeginForm("MakeDue", "Home")) { @Html.ValidationSummary(true) @for(int i = 0; i < Model.DueList.Count; i++) { <tr> <td> @Html.HiddenFor(m => m.DueList[i].id) @Html.DisplayFor(m => m.DueList[i].flat)</td> <td>@Html.DisplayFor(m => m.DueList[i].name)</td> <td>@Html.TextBoxFor(m => m.DueList[i].due)</td> </tr> } <input type="submit" class="btn btn-success" value="Update" /> } 

Note that the @Html.HiddenFor() must be inside the <td> element in order to be a valid html.

The next problem is that the model in the view is not a List<BillCheck> , but it does contain a property called DueList , which is typeof List<BillCheck> , so your POST method should be

 public ActionResult MakeDue(YourModel model) 

where YourModel is the name of the class that you used to create the view (i.e. in the @model ??? instruction). Then you should use a loop in the controller method

 foreach (var BillId in model.DueList) { var getDue = db.BillChecks.Where(p => p.id == BillId.id).FirstOrDefault(); if (getDue != null) // add this { getDue.due = BillId.due; } } db.SaveChanges(); 

Note the addition of an if (getDue != null) check if (getDue != null)

Side note: you are checking if (ModelState.IsValid) . It is recommended that the ModelState view be ModelState invalid so that the user can fix any errors.