MVC Drop Down list with entity framework

问题:

I've created an MVC project using entity framework code first. My model is simply a form that gathers information.

public class Application
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string MiddleInitial { get; set; }
    public string LastName { get; set; }
    public int SSN { get; set; }
    public DateTime DOB { get; set; }
    public string Street { get; set; }
    public string City { get; set; }
    public string State {get; set; }
    public string Zip { get; set; }
    public int HomePhone { get; set; }
    public int BusinessPhone { get; set; }
    public int MobilePhone { get; set; }

}

My goal is to create a drop down list with all of the states, but I'm finding this to be very difficult given that I've already created the database via scaffolding with views and controllers. Is there a simple way to do this and tie it in with the existing database? I've searched for almost the entire day with no luck. An overview/explanation of what to include for the model/controller/view would be amazing!

---

Update: I've created a new model named "State" with properties "Id" and "StateName" and have created some states in the database. In my "Application" controller inside the Create action method I have:

Controller

public ActionResult Create()
    {

        ApplicationDbContext db = new ApplicationDbContext();
        this.ViewData["Id"] = new SelectList(db.States.ToList(), "Id", "StateName");
        return View();
    }

View

@Html.DropDownList("Id")

Now the problem is I'm getting this error " There is no ViewData item of type 'IEnumerable' that has the key 'Id'." Would really appreciate help!

回答1:

Its quite simple. Add an IEnumerable<SelectListItem> property to your model(Here I suggest you make a ViewModel that can have the exact same properties as Application with the below code included as a property). Then you just need to build the list and send it to your view

public IEnumerable<SelectListItem> States{ get; set; }

I will assume you want to retrieve the State values from the db. Here is how you will do it:

private IEnumerable<SelectListItem> GetAllStates()
{
    IEnumerable<SelectListItem> list = from s in db.Applications
                                       select new SelectListItem
                                       {
                                           Selected = false,
                                           Text = s.State,
                                           Value = s.State
                                       };
    return list;
}

Or this...

private IEnumerable<SelectListItem> GetAllStates()
{
    IEnumerable<SelectListItem> list = db.Applications.Select(s => new SelectListItem
                                       {
                                           Selected = false,
                                           Text = s.State,
                                           Value = s.State
                                       });

    return list;
}

Then do something like this in your action:

var app = new Application
{
    States = GetAllStates()
};

return View(app);

Then finally, use Razor on the view to display the Dropdown list like this

@Html.DropDownListFor(m => m.State, Model.States, "--Select a State--")

The 1st parameter is the property of the model to update, the 2nd is the list of data, and 3rd is the default message that will be displayed

Hope this helps.

回答2:

Create a data layer that retrieves a list of what you want. Then use EF to get all the states.

//assuming you have a table of states..
var states = db.States();

The states table should be a Unique list of states.

var selectList = new List<SelectListItem>(); 
foreach(var thing in states){
    //if you got everything, thus the ID field for the value...   
   selectList.Add(new SelectListItem {Text =thing.State, Selected = false, Value = thing.ID);
}

Make sure in your Viewmodel class that selectlist is a public property.....and set to what you did above. You also need to provied a string for the view selection post back.

StatesSelectList = selectList;
public IEnumberable<SelectListItem> StatesSelectList {get;set;}
public string SelectedState {get;set;}

In your view, do this:

@Html.DropDownListFor(p=>Model.SelectedState, Model.StatesSelectList)

回答3:

Very simple Code step by step

1) In Entity Framework Class

var productsList = (from product in dbContext.Products
                     select new ProductDTO
                     {
                       ProductId = product.ProductId,
                       ProductName = product.ProductName,
                       }).ToList();

2) In Controller

ViewBag.productsList = new EntityFrameWorkClass().GetBusinessSubCategoriesListForDD();

3) In View

@Html.DropDownList("Product_ProductId", new SelectList(ViewBag.productsList, "ProductId", "ProductName"), new { @class = "form-control" })

OR

@Html.DropDownListFor(m=>m.Product_ProductId, new SelectList(ViewBag.productsList , "ProductId", "ProductName"), new { @class = "form-control" })

回答4:

I assume there is a States model that has a Id and a StateName property.

Change to the list to ViewData["State"] to ensure easy binding on POST.

Id is the value that will be sent in the POST data ie.. State = Id. The StateName is what will be displayed in the Select list. So for your model this is not correct as State is a string. So needs to be

this.ViewData["State"] = new SelectList(db.States.ToList(), "StateName", "StateName");

Then in your view

@Html.DropDownList("State")