Is there any difference in using the Read() method of the Sqldatareader object?

Question

I am running the code snippet below, however, I was left with doubt related to the method Read() of the object Sqldatareader.

using (SqlDataReader reader = cmd.ExecuteReader())
{
    if (reader.HasRows)
    {
        if (reader.Read())
        {
             pconfigWS.Usuario = reader["usuario"].ToString();
             pconfigWS.Senha = reader["senha"].ToString();
             pconfigWS.EndConWSPorto = reader["endConWSPorto"].ToString();
        }
    }
}

I wonder if there’s a difference in using While(reader.Read()), if(reader.Read()) and reader.Read()

I know that the result of the query will be only one line, however, I am with this doubt.

Does anyone know how to say ?

Thank you

Answer 1

Every call to Read() will advance the reading of the search results.

In that case, the difference would be:

//contiuna lendo o próixmo até não houver mais
while (reader.Read())
{
  ...
}

//lê o próximo e me fala se for sucedido...
if (reader.Read())
{
  ...
}

//lê o próximo
reader.Read();

I think it’s important to know that if(reader.Read()) will advance to the next record, then the next reader.Read() will be the record next, not the current.

For example, your codex explained:

using (SqlDataReader reader = cmd.ExecuteReader())
{
    if (reader.HasRows) //verifique se o leitor tem dado algum
    {
        if (reader.Read()) //lê os dados - se tiver mais de um registro, não está sendo lido
        {
             pconfigWS.Usuario = reader["usuario"].ToString();
             pconfigWS.Senha = reader["senha"].ToString();
             pconfigWS.EndConWSPorto = reader["endConWSPorto"].ToString();
        }
    }
}

And an example that can give unexpected results:

using (SqlDataReader reader = cmd.ExecuteReader())
{
    List<PConfigWS> resultados = new List<obj>();
    if (reader.Read())
    {
        while (reader.Read())
        {
             var pconfigWS = new PConfigWS();
             pconfigWS.Usuario = reader["usuario"].ToString();
             pconfigWS.Senha = reader["senha"].ToString();
             pconfigWS.EndConWSPorto = reader["endConWSPorto"].ToString();
             resultados.Add(pconfigWS);
        }
    }
}

In this case, the first record would be ignored (because of the if(reader.Read()), that probably wouldn’t be the desired result. Use reader.HasRows it would be the right way, as you used.

There is not necessarily 'good practice' between these functions - they are literally the same function, being used in different forms. It all depends on whether you are reading just one record or several.