Use string to reference variable

Question

I wish to move on to the function execSQL the name of the variable I want to use in base.consulta() and from the string SQL, directly pass the variable to the function base.consulta(), that is, pass the variable that has the same name as the string.

An example for you to have an idea of what I’m looking for.

OBS: I know the way it is doesn’t work and I know why.

// variáveis com algum SQL
string sqlConsultaEspecifica = "...";
string sqlMonitoramento = "...";
string sqlVerificacao = "...";

function execSQL(string sql = "sqlMonitoramento") {
  // ...
  // realizar algumas ações aqui
  // ...
  return base.consulta(sql);
}

Is it possible to do this? How could I do this?

Answer 1

First of all this syntax is not C#.

It is always possible to build a sophisticated mechanism that allows this. But for what?

One of the ways is to use reflection, but almost 100% of the cases that one uses reflection is doing something wrong. It is a tremendous complication, a huge loss of performance, chance of failure, of insecurities for a gain that is often small or zero. I can almost guarantee you that this case is zero.

Where is the call of that method execSQL()? It is there where you will define what to pass. If the method already knows what it wants, then it makes no sense to use this.

If these variables are local to a method, it makes zero sense to try to do something like this. If the variables are of the object it is quite simple:

void ExecSQL() {
    ...
    return base.consulta(sqlMonitoramento);
}

If it is a local variable the reflection does not work. If it is a class variable or instance the reflection is unnecessary, zero gain.

If you want to do things differently, go to string different.

void ExecSQL(string sql) {
    ...
    return base.consulta(sql);
}

There to call you pass, for example:

ExecSQL(sqlMonitoramento);

I put in the Github for future reference.

This code is very strange and may have an architectural flaw there. I can’t say because it has no context.

Answer 2

To obtain the value of a variable of some object it is possible to do as follows:

Imagine an object named "Test" with 2 properties (Description and Name).

Let’s say I want to take the value of some of these two properties, but I still don’t know which, so follow an example code with one of the ways to solve this.

Teste teste = new Teste()
        {
            Descricao = "Descrição aqui",
            Nome = "nome aqui"
        };

        string valorDesejado = teste.GetType().GetProperty("Descricao").GetValue(teste, null).ToString();

Inside the "Getproperty()" goes the name of the variable that I want to get the value. So just adapt.

Answer 3

You can try this way:

public void execSQL(string sql)
{
    //A variável "valor" vai estar com o valor da variável que você passou como parâmetro.
    //O objeto "classe" deve ser o objeto que possui a sua variável "sql"
    string valor = teste.GetType().GetProperty(sql).GetValue(classe, null).ToString()   
}

The call to the method would look like this:

//Aqui você iria passar a variável que gostaria de passar o nome para o método, porém ela deve ser visível para esse escopo
execSQL(nameof(sqlMonitoramento));