I am accessing data from a Category's ICollection<Product> Products
property. If you look at my controller code below, using the second select, I change each product's Form
from a Product entity into a ProductViewModel which returns an IQueryable<IEnumerable<ProductViewModel>>
.
Finally, with the ToListAsync()
method, the model returns a List<IEnumerable<ProductViewModel>>
which is not accepted by my View
.
My controllers model is this:
var model = (await db.Categories.Where(c => c.Id == id).Select(p => p.Products.Select(x => new
ProductViewModel { Id = x.Id, Name = x.Name, ByteImage = x.Image, Price = x.Price})).ToListAsync());
return View(model);
The return type for this model is List<IEnumerable<ProductViewModel>>
and I cannot iterate through this model inside my View to display the data.
View model given to the View
is:
@model IEnumerable<ProductViewModel>
.
This is the error message I get:
Compiler Error Message: CS0411: The type arguments for method 'DisplayNameExtensions.DisplayNameFor(HtmlHelper, Expression>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
Source Error:
Line 14: <tr>
Line 15: <th>
Line 16: @Html.DisplayNameFor(model => model.Name)
Line 17:
Line 18: </th>
ProductViewModel:
public class ProductViewModel
{
public int Id { get; set; }
[Required, Display(Name="Product Name")]
public string Name { get; set; }
[Required, DataType(DataType.Upload)]
public HttpPostedFileBase Image { get; set; }
public string OutputImage { get; set; }
public Byte[] ByteImage { get; set; }
[Required]
public Decimal Price { get; set; }
public static byte[] ConvertToByte(ProductViewModel model)
{
if (model.Image != null)
{
byte[] imageByte = null;
BinaryReader rdr = new BinaryReader(model.Image.InputStream);
imageByte = rdr.ReadBytes((int)model.Image.ContentLength);
return imageByte;
}
return null;
}
// ViewModel => Model | Implicit type Operator
public static implicit operator Product(ProductViewModel viewModel)
{
var model = new Product
{
Id = viewModel.Id,
Name = viewModel.Name,
Image = ConvertToByte(viewModel),
Price = viewModel.Price
};
return model;
}
// Model => ViewModel | Implicit type Operator
public static implicit operator ProductViewModel(Product model)
{
var viewModel = new ProductViewModel
{
Id = model.Id,
Name = model.Name,
OutputImage = string.Format("data:image/jpg;base64,{0}", Convert.ToBase64String(model.Image)),
Price = model.Price
};
return viewModel;
}
}
This is the View Index:
@model List<ValueVille.Models.ProductViewModel>
@using MvcApplication8.Models
@{
ViewBag.Title = "Index";
}
<h2>Index</h2>
<p>
@Html.ActionLink("Create New", "Create")
</p>
<table class="table">
<tr>
<th>
@Html.DisplayNameFor(model => model.Name)
</th>
<th>
@Html.DisplayNameFor(model => model.Image)
</th>
<th>
@Html.DisplayNameFor(model => model.Price)
</th>
<th></th>
</tr>
@foreach (var item in Model) {
<tr>
<td>
@Html.DisplayFor(modelItem => item.Name)
</td>
<td>
@Html.DisplayFor(modelItem => item.Image)
</td>
<td>
@Html.DisplayFor(modelItem => item.Price)
</td>
<td>
@Html.ActionLink("Edit", "Edit", new { id=item.Id }) |
@Html.ActionLink("Details", "Details", new { id=item.Id }) |
@Html.ActionLink("Delete", "Delete", new { id=item.Id })
</td>
</tr>
}
</table>
You need to use SelectMany
instead:
(await db.Categories
.Where(c => c.Id == id)
.SelectMany(p => p.Products.Select(x => new ProductViewModel { Id = x.Id, Name = x.Name, ByteImage = x.Image, Price = x.Price }))
.ToListAsync());
SelectMany
is useful when you want to project from multiple sequences into a single (flat) sequence.
As per your update:
Since your model is actually List<ProductViewModel>
, when you want to display the name of certain property, you need to point to an actual ProductViewModel
instance within that list.
For example:
@Html.DisplayNameFor(model => model[0].Name)
See MSDN
At the moment, you sequence looks like this
[ [model1, model2, model3], [model4, model] ]
to flatten it you could
model.SelectMany(m => m)
for
[ model1, model2, model3, model4, model5 ]
(if that's really what you want)
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