Posting DropDownList value from View to Controller in MVC4 - asp.net-mvc-4

Question

I have a MVC4 application and although I have get parameters for my DropDownList from the database, I encounter some kind of problems while posting the DropDownList value to the database. There is lots of samples for different approach, but I would like to apply a method without using an extra approach i.e. Ajax, Javascript, etc. On the other hand, I have run into "FormCollection" to pass data, but I am not sure if FormCollection is the best way in this scene. Here are some part of the view, controller and model I use:
View:
#using (Html.BeginForm("Add", "Product", FormMethod.Post,
new { enctype = "multipart/form-data" }))
{
<p>Product Type : #Html.DropDownListFor(m => m.SelectedLookupId, new SelectList(Model.Lookups.Where(x => x.LookupType == "Product Type"), "LookupID", "LookupValue"), "--- Select ---") </p>
Controller:
[HttpPost]
public ActionResult Add(Product product)
{
if (ModelState.IsValid)
{
product.ProductType = // ??? Cannot get the SelectedLookupId
...
repository.SaveProduct (product);
TempData["message"] = string.Format("{0} has been saved", product.Name);
return View("Completed");
}
else
{
//there is something wrong with the data values
return View(product);
}
}
ViewModel:
public class ProductViewModel
{
public IEnumerable<Product> Products { get; set; }
public IEnumerable<Lookup> Lookups { get; set; } //Lookup for Product Types
public int SelectedLookupId { get; set; }
public Product Product { get; set; }
}
Thanks in advance for your helps.

Answer 1

Your action method should be receiving the view model, not the Product itself, like so:
[HttpPost]
public ActionResult Add(ProductViewModel productViewModel)
Unless I'm confused. But I assume the view snippet you posted above is from the Add view and that view's model is of type ProductViewModel. In your action method you are returning the Add view when the model state is invalid however you are passing a Product to that view. Again I may be confused because this should give you a runtime error that the types don't match.

Answer 2

Thanks for reply. Actually by using ViewModel rather than View, I have managed to solve the problem. On the other hand, after some research, I have applied another effective method in order to populate Dropdownlist without needing ViewModel. Furthermore with this example, I could use multiple foreign keys on the same Lookup table as shown below. Here is an an Applicant entity having 3 foreign keys and Lookup entity related to these keys. What I wanted to achieve with this example is exactly to use a Lookup table for only several Dropdownlist parameters i.e. Gender, Yes/No, Status,... due to no needing to create a table for the several parameters (these parameters are distinguished LookupType property on Lookup table). Here is the full example (I have shorted unrelated properties for brevity) below:
Applicant Entity:
public class Applicant
{
[Key]
public int ApplicantID { get; set; }
public string Name { get; set; }
public string Surname { get; set; }
// for using "Multiple foreign keys within same table using Fluent API"
public int? HasDoneAnyProject { get; set; }
public int? IsInterestedAnyProgramme { get; set; }
public int? InterestedProgrammeId { get; set; }
public virtual Lookup PrimaryLookup { get; set; }
public virtual Lookup SecondaryLookup { get; set; }
public virtual Lookup TertiaryLookup { get; set; }
}
Lookup Entity:
public class Lookup
{
[Key]
public int LookupID { get; set; }
public string LookupType { get; set; }
public string LookupValue { get; set; }
// for using "Multiple foreign keys within same table using Fluent API"
public virtual ICollection<Applicant> PrimaryLookupFor { get; set; }
public virtual ICollection<Applicant> SecondaryLookupFor { get; set; }
public virtual ICollection<Applicant> TertiaryLookupFor { get; set; }
}
DbContext:
public class EFDbContext : DbContext
{
public DbSet<Applicant> Applicants { get; set; }
public DbSet<Lookup> Lookups { get; set; }
//for using "Multiple foreign keys within same table using Fluent API"
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Applicant>()
.HasOptional(b => b.PrimaryLookup)
.WithMany(a => a.PrimaryLookupFor)
.HasForeignKey(b => b.HasDoneAnyProject)
.WillCascadeOnDelete(false);
modelBuilder.Entity<Applicant>()
.HasOptional(b => b.SecondaryLookup)
.WithMany(a => a.SecondaryLookupFor)
.HasForeignKey(b => b.IsInterestedAnyProgramme)
.WillCascadeOnDelete(false);
modelBuilder.Entity<Applicant>()
.HasOptional(b => b.TertiaryLookup)
.WithMany(a => a.TertiaryLookupFor)
.HasForeignKey(b => b.InterestedProgrammeId)
.WillCascadeOnDelete(false);
}
}
Controller:
private void PopulateLookupsDropDownList(string lookupType, string foreignKey, object selectedLookups = null)
{
var lookupsQuery = repository.Lookups
.Select(x => x)
.Where(x => x.LookupType == lookupType)
.OrderBy(x => x.ParentLookupID).ToList();
ViewData[foreignKey] = new SelectList(lookupsQuery, "LookupID", "LookupValue", selectedLookups);
}
and for calling the Method for each of three Dropdownlist:
PopulateLookupsDropDownList("YesNo", "HasDoneAnyProject", applicant.HasDoneAnyProject);
PopulateLookupsDropDownList("YesNo", "IsInterestedAnyProgramme", applicant.IsInterestedAnyProgramme);
PopulateLookupsDropDownList("Programme", "InterestedProgrammeId", applicant.InterestedProgrammeId);
View: : Populating each of three Dropdownlist from the same Lookup table with different LookupType parameter:
<label>Has done any project before?</label>
#Html.DropDownList("HasDoneAnyProject", "---- Select ----")
<label>Are you interested in any programme?</label>
#Html.DropDownList("IsInterestedAnyProgramme", "---- Select ----")
<label>Interested programme name?</label>
#Html.DropDownList("InterestedProgrammeId", "---- Select ----")
I hope this approach will be useful for those who want to populate Dropdownlists from the same Lookup table. On the other hand, it is not only suitable for this, also can be used for populating Dropdownlists from different tables.
Regards.