Populating dropdown and adding new row to db with Entity Framework - asp.net-mvc-3

Question

I want to add a post with category, my Add action in BlogController is like this :
private readonly IBlogPostRepository _blogPostRepository;
private readonly ICategoryRepository _categoryRepository;
public BlogController()
{
_blogPostRepository = new BlogPostRepository(new SiteContext());
_categoryRepository = new CategoryRepository(new SiteContext());
}
public BlogController(IBlogPostRepository blogPostRepository, ICategoryRepository categoryRepository)
{
_blogPostRepository = blogPostRepository;
_categoryRepository = categoryRepository;
}
public ActionResult Add()
{
ViewData["categoryList"] = _categoryRepository.GetAllCategory();
return View("Add");
}
[HttpPost]
public ActionResult Add(BlogPost blogPost)
{
if (ModelState.IsValid)
{
blogPost.PublishDate = DateTime.Now;
_blogPostRepository.AddPost(blogPost);
_blogPostRepository.Save();
return RedirectToAction("Add");
}
return new HttpNotFoundResult("An Error Accoured while requesting your order!");
}
My first question is that why I can't cast category list to SelectList in razor to select a category via DropDownList? My code in view is like this:
<div>
#Html.LabelFor(b => b.Category)
#Html.DropDownList("Category", ViewData["categoryList"] as SelectList)
#Html.ValidationMessageFor(b => b.Category)
</div>
My second question is: how can I add category in Add action with POST request?

Answer 1

To use a collection for a dropdown, it has to be of type IEnumerable<SelectListItem>, which SelectList is. You can't take an arbitrary collection of objects and just cast it to a SelectList.
I like to use an extension method for creating an IEnumerable<SelectListItem>, check out this:
public static class SelectListExtensions
{
public static IEnumerable<SelectListItem> ToSelectList<T>(this IEnumerable<T> source)
{
return ToSelectList(source, null);
}
public static IEnumerable<SelectListItem> ToSelectList<T>(this IEnumerable<T> source, string defaultOption)
{
return ToSelectList(source, value => value, value => value.ToString(), null);
}
public static IEnumerable<SelectListItem> ToSelectList<T, TDataValue>(
this IEnumerable<T> source,
Func<T, TDataValue> dataValueSelector,
Func<T, string> dataTextSelector)
{
return ToSelectList(source, (value, index) => dataValueSelector(value), dataTextSelector, null);
}
public static IEnumerable<SelectListItem> ToSelectList<T, TDataValue>(
this IEnumerable<T> source,
Func<T, int, TDataValue> dataValueSelector,
Func<T, string> dataTextSelector)
{
return ToSelectList(source, dataValueSelector, dataTextSelector, null);
}
public static IEnumerable<SelectListItem> ToSelectList<T, TDataValue>(
this IEnumerable<T> source,
Func<T, TDataValue> dataValueSelector,
Func<T, string> dataTextSelector,
string defaultOption)
{
return ToSelectList(source, (value, index) => dataValueSelector(value), dataTextSelector, defaultOption);
}
public static IEnumerable<SelectListItem> ToSelectList<T, TDataValue>(
this IEnumerable<T> source,
Func<T, int, TDataValue> dataValueSelector,
Func<T, string> dataTextSelector,
string defaultOption)
{
var list = source.Select((item, index) => new SelectListItem
{
Value = dataValueSelector(item, index).ToString(),
Text = dataTextSelector(item),
}).ToList();
if (defaultOption == null) return list;
list.Insert(0, new SelectListItem { Text = defaultOption, Value = "-1" });
return list;
}
}
You can then use this extension method in your controller:
public ActionResult Add()
{
ViewData["categoryList"] = _categoryRepository.GetAllCategory()
.ToSelectList(c => c.Id, c => c.Name);
return View("Add");
}
Assuming that your Category has the properties Id and Name...
And then use it in your view:
#Html.DropDownList("Category", ViewData["categoryList"] as IEnumerable<SelectListItem>)
On a side note, I would recommend that you use models to pass to your (strongly typed) views, as opposed to using ViewData/ViewBag. It saves you a lot of trouble the day you're going to refactor something and it also gives you good tooling help (intellisense).