Compare string to Enum, inside the lambda?

Question

the problem is:

I have a dropdownlist loaded from an Enum, which can come with the null value of the screen.

listaItensSolicitados = os.Site == null ? 
   this.itemSolicitadoService.Consultar(o =>
            o.ItemServico.Servico.Chave == 9 &&
            o.ChaveOrgao == os.Orgao.Chave && o.Numero.Contains(ramal)
            && o.CategoriaDiurna == ddlCategoriaDiurna
            && o.Instalado == true
            && (o.Depreciado == null
            || o.Depreciado == false)).Take(200).ToList() :

As you know, you can’t use ToString() within the lambda, I wonder if there’s a way I can make that comparison, in my ActionResult i get from the screen the value of DDL as string, and when comes the value null, doesn’t work.

@Edit

This is my enum:

public enum CategorizacaoRamaisEnum : int
{     
    [Description("Categoria 1")]
    Categoria1 = 1,
    [Description("Categoria 2")]
    Categoria2,
    [Description("Categoria 3")]
    Categoria3,
    [Description("Categoria 4")]
    Categoria4,
    [Description("Categoria 5")]
    Categoria5,
    [Description("Categoria 6")]
    Categoria6,
    [Description("Categoria 7")]
    Categoria7,
    [Description("Categoria 8")]
    Categoria8,
    [Description("Categoria 9")]
    Categoria9,
    [Description("Categoria 10")]
    Categoria10,
    [Description("Categoria 11")]
    Categoria11       
}

@Edit 2

Creation of dropdownlist:

@Html.DropDownList("ddlCategoriaDiurna", 
           (ViewBag.CategoriaDiurna as SelectList), 
            string.Empty)                   

Answer 1

The value of this ddlCategoriaDiurna comes from Category 1, as an example?

If so, you could read the value Description of your enum

public static string Descricao(this System.Enum itemEnum)
{
   DescriptionAttribute descricao = (DescriptionAttribute)itemEnum.GetType()
        .GetField(itemEnum.ToString())
          .GetCustomAttributes(typeof(DescriptionAttribute), false)
        .FirstOrDefault();
   string retorno = itemEnum.ToString();
   if (descricao != null)
       retorno = descricao.Description;
   return retorno;
}

In a enum

public enum Carro
{
    [Description("Carro Mercedes")]
    Mercedes,
    [Description("Carro Ferrari")]
    Ferrari,
    [Description("Carro Jaguar")]
    Jaguar,
    Porche
}

An example of use with lambda

Carro[] carros = new []{ Carro.Ferrari, Carro.Jaguar };
string texto = Carro.Ferrari.Descricao();
// texto = "Carro Ferrari"
if (carros.Any(c => c.Descricao() == texto))
    Console.WriteLine("Correto");
else
    Console.WriteLine("Incorreto");

// Resultado: Correto

Answer 2

I was able to solve it this way :

I created a method to find the string passed on screen on my Enum, if it was null, return to categorie1 by default :

public CategorizacaoRamaisEnum retornarEnum(string ddlSelecionado) 
{
     return string.IsNullOrEmpty(ddlSelecionado) 
             ? CategorizacaoRamaisEnum.Categoria1 
             :(CategorizacaoRamaisEnum)System.Enum.Parse(typeof(CategorizacaoRamaisEnum),
               ddlSelecionado);
}

I validated the return and if the past value existed in enum:

CategorizacaoRamaisEnum retornoCategoriaDiurna = retornarEnum(ddlCategoriaDiurna);
bool result = Enum.GetNames(typeof(CategorizacaoRamaisEnum)).Contains(ddlCategoriaDiurna);

And finally in mine query Linq:

listaItensSolicitados = os.Site == null ?      this.itemSolicitadoService.Consultar(o =>
            o.ItemServico.Servico.Chave == 9 &&
            o.ChaveOrgao == os.Orgao.Chave
            && o.Numero.Contains(ramal)
            && o.Instalado == true          
            && (result ? o.CategoriaDiurna == retornoCategoriaDiurna : o.Instalado == true)
            && (o.Depreciado == null
            || o.Depreciado == false)).Take(200).ToList()

I know it got redundant in the fake ternary, but that way it solved my problem. If anyone thinks of a more elegant way, kindly put it there, that will help me improve.

Answer 3

From what I understand the problem is that you have an "Enum" with strings.

Point 1: If you do not explicitly state the value of that enum it assumes the launch order and infers numbers

Example:

enum Meses:short
{
    Janeiro,
    Fevereiro,
    ...
}

In this case the values would be 0, 1 and so on.

The best solution I can give you is to map this enum to a dictionary or to create a class enum with the strings you want to compare. Another solution would be to create an auxiliary table in the database to have these values registered there, in case they can be changed or added and not leave this enum hard coded.