How to compare with Guid Mvc

You just need to compare the property with Guid.Empty

Eg:

cliente.ClienteGuid == Guid.Empty;

About the displayed code: This second if, is not necessary, this way it will work, but it will bring you some problems later. For example, every time you create a new property you will have to enter the save method and edit it.

You can simplify everything to:

public void Salvar(Cliente cliente)
{
    if(cliente.ClienteGuid == Guid.Empty)
    {
        cliente.DataCadastro = DateTime.Now;
        _contexto.Clientes.Add(cliente);
    }
    else
    {
        _contexto.Entry(cliente).State = EntityState.Modified;
    }

    _contexto.SaveChanges();
}

  

I may have some typos because I wrote on my cell phone, anything tells me the comments I make as soon as I can.

Test whether the variable of type Guid is empty :

Example:

namespace ConsoleApplication5
{
    class Program
    {
        static void Main(string[] args)
        {
            Guid Id = Guid.Empty;

            if (Id == Guid.Empty)
            {
                Console.WriteLine("Guid is empty");                
            }

            Id = Guid.NewGuid();

            if (!(Id == Guid.Empty))
            {
                Console.WriteLine("Guid not empty");
            }

            Console.ReadKey();

        }
    }
}

DEMO

Another way that can happen is how much we define the type System.Nullable :

static void Main(string[] args)
{
    Guid? Id = null;

    if (Id.HasValue)
    {
        Console.WriteLine("Guid is not null");                
    }
    else
    {
        Console.WriteLine("Guid is null");                
    }

    Id = Guid.NewGuid();

    if (Id.HasValue)
    {
        Console.WriteLine("Guid not null");
    }

    Console.ReadKey();

}

DEMO

In your question, the code snippet can vary in these ways:

Guid.Empty

public void Salvar(Cliente cliente)
{
    if (cliente.ClienteID == Guid.Empty)
    {                
        cliente.DataCadastro = DateTime.Now;
        _contexto.Clientes.Add(cliente);
    }
    else
    {                
        Cliente cli = _contexto.Clientes.Find(cliente.ClienteID);

        if (cli != null)
        {
            cli.Nome = cliente.Nome;
            cli.Cpf = cliente.Cpf;
            cli.Telefone = cliente.Telefone;
            cli.Email = cliente.Email;
            cli.Cep = cliente.Cep;
            cli.Endereco = cliente.Endereco;
            cli.Bairro = cliente.Bairro;
            cli.Numero = cliente.Numero;
            cli.Complemento = cliente.Complemento;
            cli.DataCadastro = cli.DataCadastro;
        }
    }
    _contexto.SaveChanges();
}

Guid == null

public void Salvar(Cliente cliente)
{
    if (!cliente.ClienteID.HasValue)
    {                
        cliente.DataCadastro = DateTime.Now;
        _contexto.Clientes.Add(cliente);
    }
    else
    {                
        Cliente cli = _contexto.Clientes.Find(cliente.ClienteID);

        if (cli != null)
        {
            cli.Nome = cliente.Nome;
            cli.Cpf = cliente.Cpf;
            cli.Telefone = cliente.Telefone;
            cli.Email = cliente.Email;
            cli.Cep = cliente.Cep;
            cli.Endereco = cliente.Endereco;
            cli.Bairro = cliente.Bairro;
            cli.Numero = cliente.Numero;
            cli.Complemento = cliente.Complemento;
            cli.DataCadastro = cli.DataCadastro;
        }
    }
    _contexto.SaveChanges();
}

References:

• Estrutura Guid

• Campo Guid.Empty

• Estrutura Nullable<T>