实体框架中导航属性的属性总和

Question

I would like to sum data displayed on the web page from a column.

I tried using

ViewBag.Total = bookingdb.Packages.Sum(x => x.PkgBasePrice);

which gets me the sum of whats in the database obviously,

And I tried

@Model.Sum(i => i.Package.PkgBasePrice)

as well where I am getting an null exception error.

I have 3 tables connected, Bookings packages and customers through EF.

The view form has the parent table booking so if I try to add anything else for example

@Model.Sum(i => i.TravelerCount)

it works, and the problem is when it goes like i.table.column that gives an error.

I would like to sum all PkgBasePrice data shown on the web page as those numbers are filtered through customers and are repeated so sum through database is not an option.

This is from View

@model IEnumerable<Online.Models.Booking>
@{
  ViewBag.Title = "Bookings";
}



@*<h1>Welcome @Session["CustomerId"].ToString()</h1>*@
<h1>Welcome @Session["Username"].ToString()</h1>

<p>
<h2> Your Bookings </h2>
</p>
<table class="table">
<tr>
    <th>
        @Html.DisplayNameFor(model => model.BookingDate)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.BookingNo)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.TravelerCount)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Customer.CustFirstName)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Customer.CustLastName)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Package.PkgName)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.PkgBasePrice)
    </th>
    <th></th>
</tr>

   @foreach (var item in Model.Where(ModelItem => 
 ModelItem.CustomerId.Equals(Session["CustomerId"])))
 {
    <tr>
        @*<td>
                @Html.DisplayFor(modelItem => item.Customer.CustomerId)
            </td>*@
        <td>
            @Html.DisplayFor(modelItem => item.BookingDate)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.BookingNo)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.TravelerCount)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Customer.CustFirstName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Customer.CustLastName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Package.PkgName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Package.PkgBasePrice)
        </td>
        <td>
            @Html.ActionLink("Package Details", "Details", new { id = 
item.BookingId })
        </td>
    </tr>

}
</table>
@Model.Sum(i => i.Package.PkgBasePrice) //doesn't Work
<div> @ViewBag.Total </div>
<div>
@Html.ActionLink("Personal Information", "Customer", "Customer")
</div>

Answer 1

Problem is when you are loading the Booking List in the controller method its not loading the relevant Package for each Booking . To load relevant Package for each Booking in the Booking List you can use Incldue as follows:

var bookingList = bookingdb.Bookings.Include(b= > b.Package).ToList();
return View(bookingList);

Moreover to ensure that a Booking must containing a Package , write your query as follows. Otherwise if any Booking contain no Package it will throw null reference exception during the Sum .

@Model.Where(b => b.Package != null).Sum(i => i.Package.PkgBasePrice)

Hope it will work for you now.

Answer 2

The first question to ask i suppose is “Where are you getting the data from? Are you accessing entities directly in your view?”

If so, I'd strongly discourage that. You are better off using view models and populating that view model in your business layer. Your views should just be binding to a view model and displaying its values; you shouldn't be mixing logic into your view this way.

The second question would be “are you adding the includes for the additional navigation properties”? Null values can sometimes be caused by the navigation property not being included in the underlying query.

Fundamentally, I don't think there's enough information here to help fully