Dropdown List from a table in the Database

Question

I’m developing in Asp.net-mvc and I have the following problem:

I need to create a dropdown list that displays the name of the instructors registered in the Database.

CRUD is already working perfectly. I used the Entity Framework to register students and instructors, each in its respective table in the Database.

In the view student registration, there is a input to manually insert which id the instructor of that student to be registered, but I want it to be a list with the names of all instructors registered in the table Instrutor, and so, automatically insert it into the table Aluno the id of the instructor I selected.

Here are my tables:

Below, the View student registration:

Taking advantage of the question, how do I edit the text on label?

Answer 1

It’s basically two steps.

Upload Instructor data to ViewBag

This step is simple. It can be done like this:

ViewBag.Instrutores = contexto.Instrutores.ToList()

Utilize @Html.DropDownListFor()

In the View, you will need to assemble a SelectList within the DropDownList. The use may seem a little scary as below, but I will explain argument to make it clearer:

@Html.DropDownListFor(model => model.InstrutorId, ((IEnumerable<Instrutor>)ViewBag.Instrutores).Select(option => new SelectListItem
{
    Text = option.NomeInstrutor,
    Value = option.InstrutorId.ToString(),
    Selected = (Model != null) && (Model.InstrutorId == option.InstrutorId)
}), "Selecione um Instrutor...", new { @class = "form-control" })

The first argument is the field of Id:

model => model.InstrutorId

Reads as follows::

Having the model inside the variable model, use InstrutorId.

The second argument is the biggest. It is not very complex, although it seems.

((IEnumerable<Instrutor>)ViewBag.Instrutores).Select(option => new SelectListItem
{
    Text = option.NomeInstrutor,
    Value = option.InstrutorId.ToString(),
    Selected = (Model != null) && (Model.InstrutorId == option.InstrutorId)
})

This part here:

((IEnumerable<Instrutor>)ViewBag.Instrutores)

Converts ViewBag.Instrutores (the one we selected in Controller) to a list of instructors. IEnumerable is one of the interfaces of List.

Then we take this list and "select", for each element of it, an element of the type SelectListItem:

Select(option => new SelectListItem
{
    Text = option.NomeInstrutor,
    Value = option.InstrutorId.ToString(),
    Selected = (Model != null) && (Model.InstrutorId == option.InstrutorId)
})

That is, we are actually creating, for each instructor, a SelectListItem, filled with instructor attributes. Note that I put each instructor in a variable option, and need to fill in Text (the field that will appear), Value (the value field, ie the instructor id), and Selected (which indicates which field will appear selected, and which I do this way for the edit screen).

Finally, the third argument indicates which text of the empty option:

"Selecione um Instrutor..."

And the last argument are additional HTML attributes that you might want to use. This one is to format the field as a input to the Bootstrap:

new { @class = "form-control" }

how do I edit the text in label?

If you will not internationalize, decorate the Model with

[DisplayName("Instrutor")]
public int InstrutorID { get; set; }

If it is, see this response.