Dropdown - ASP.NET MVC

Question

I’m a beginner in ASP.NET MVC and I need to create a Dropdown in a vehicle registration form where I can choose only one driver related to the vehicle that is previously registered in the database (created via Entity Framework). My code is currently like this:

Conductor

public class Condutor
{
    public int CondutorId { get; set; }

    [Required]
    public int Matricula { get; set; }

    [Required]
    public string PrimeiroNome { get; set; }

    [Required]
    public string UltimoNome { get; set; }

    [Required]
    public string CPF { get; set; }
}

Vehicle

public class Veiculo
{
    public int Id { get; set; }

    [Required]
    public string Modelo { get; set; }

    [Required]
    public string Marca { get; set; }

    [Required]
    public string Tipo { get; set; }
}

Controller

[AutorizacaoFilter] // filtro de autorizacao, localizado na pasta "Filters"
public class VeiculoController : Controller
{
    // atributos do controller para acesso ao banco de dados
    private VeiculoDAO dao;

    // construtor da classe
    public VeiculoController(VeiculoDAO dao)
    {
        this.dao = dao;
    }

    public IActionResult Index()
    {
        IList<Veiculo> lista = dao.Lista();
        return View(lista);
    }


    [HttpPost]
    public IActionResult IncluirVeiculo(Veiculo veiculo)
    {
        dao.IncluirVeiculo(veiculo);
        return RedirectToAction("Index");   
    }


    public IActionResult Cadastro()
    {
        var model = new Veiculo();
        return View(model);

    }


    // remove um veículo, através do seu id cadastrado na tabela do banco de dados
    public IActionResult RemoverVeiculo(int id)
    {
        dao.RemoverVeiculo(id);
        return RedirectToAction("Index");
    }


    // localiza um veículo pelo seu Id e o exibe na View "Ver Cadastro", para ser editado
    public IActionResult VerCadastro(int id)
    {
        Veiculo veiculo = dao.BuscaVeiculoPorId(id);
        return View(veiculo);
    }


    // edita o registro do veículo e reflete as alterações no BD
    [HttpPost]
    public IActionResult EditarVeiculo(Veiculo veiculo)
    {
        dao.AtualizaCadastro(veiculo);
        return RedirectToAction("Index");
    }

    public IActionResult BuscaVeiculo(string termo)
    {
        IList<Veiculo> veiculos = dao.BuscaPeloTermo(termo);
        return View("Index", veiculos);
    }

}

View

Ignore Enum, it was just for testing, while I couldn’t solve Dropdown

@model Veiculo

<div class="container">
	<br />
	<h2>Cadastrar veículo</h2>
	<br />

	<form class="form-horizontal" action="/Veiculo/IncluirVeiculo" method="post">
		<div class="form-group">
			<label class="control-label col-sm-2" for="text">Modelo:</label>
			<div class="col-sm-10">
				<input type="text" class="form-control" id="modelo" style="max-width:50%" placeholder="Ex: Palio, Gol, Corsa, etc" name="modelo" />
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="text">Marca:</label>
			<div class="col-sm-10">
				<input type="text" class="form-control" id="marca" style="max-width:50%" placeholder="Ex: Chevrolet, Honda, Nissan, etc" name="marca" />
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="text">Tipo:</label>
			<div class="col-sm-10" style="max-width:43%">
				@Html.DropDownListFor(v => v.Tipo,
		 new SelectList(Enum.GetValues(typeof(Tipo))),
		 "-- Escolha uma opção --",
		 new { @class = "form-control"})
			</div>
		</div>
		<div class="form-group">
			<div class="col-sm-offset-2 col-sm-10">
				<button type="submit" class="btn btn-success">Salvar</button>
				<button type="reset" class="btn btn-info">Limpar dados</button>
			</div>
		</div>
	</form>
</div>

Solving this example, the idea is to use other dropdowns as well, among different models. The current difficulty of mine was that, as the View is strongly typed in Vehicle, I could not create this "link" with the Driver class.

In this case, how could I create this type of Dropdown, via Entity Framework using LINQ and LAMBDA?

Answer 1

You can use Viewbag to pass a listing from Controller to the View. And to make the relationship between Veiculo and Condutor would have to create a property Condutor in class Veiculo.

Would look like this:

In class VeiculoController in action Cadastro (if this is really the action of your sign-up view), you load Viewbag with the list of Drivers.

public IActionResult Cadastro()
{
    var model = new Veiculo();

    var condutores = dbContext.Condutor.Select(c => new SelectListItem()
        {
            Value = c.CondutorId.ToString(),
            Text = c.PrimeiroNome
        });

    ViewBag.Condutores = condutores;

    return View(model);
}

For you to retrieve the Condutor selected and save it on Veiculo, needs to have relationship of Condutor in the Veiculo.

public class Veiculo {

public int Id { get; set; }

[Required]
public string Modelo { get; set; }

[Required]
public string Marca { get; set; }

[Required]
public string Tipo { get; set; }

public Condutor CondutorVeiculo { get; set; }

}

And finally in view would look like this:

 @Html.DropDownListFor(model => model.CondutorVeiculo.CondutorId, (IEnumerable<SelectListItem>)ViewBag.Condutores, new { @id = "ddlCondutores", @class = "form-control" })

See if this works for you.

Answer 2

Dropdown worked correctly, with new options added to the list as drivers are registered. However, several problems in the Vehicle CRUD. One of them is the Exception 'Sqlexception: Cannot Insert Explicit value for Identity column in table 'Conductor' when IDENTITY_INSERT is set to OFF." when registering a new vehicle. Below, follow the tables (created via Migrations in the Entity Framework):

Table Vehicles

CREATE TABLE [dbo].[Veiculos] (
[Id]                        INT NOT NULL,
[Modelo]                    NVARCHAR (MAX) NOT NULL,
[Tipo]                      NVARCHAR (MAX) NOT NULL,
[Marca]                     NVARCHAR (MAX) NOT NULL,
[CondutorVeiculoCondutorId] INT            NULL,
CONSTRAINT [PK_Veiculos] PRIMARY KEY CLUSTERED ([Id] ASC),
CONSTRAINT [FK_Veiculos_Condutor_CondutorVeiculoCondutorId] FOREIGN KEY ([CondutorVeiculoCondutorId]) REFERENCES [dbo].[Condutor] ([CondutorId])

);

Table Conductor

CREATE TABLE [dbo].[Condutor] (
[CondutorId]                INT            IDENTITY (1, 1) NOT NULL,
[Matricula]                 INT            NOT NULL,
[PrimeiroNome]              NVARCHAR (MAX) NOT NULL,
[UltimoNome]                NVARCHAR (MAX) NOT NULL,
[CPF]                       NVARCHAR (MAX) NOT NULL,
[CondutorVeiculoCondutorId] INT            NULL,
CONSTRAINT [PK_Condutor] PRIMARY KEY CLUSTERED ([CondutorId] ASC),
CONSTRAINT [FK_Condutor_Condutor_CondutorVeiculoCondutorId] FOREIGN KEY ([CondutorVeiculoCondutorId]) REFERENCES [dbo].[Condutor] ([CondutorId])

);