Question :
I have combobox that is receiving data from a table in my MySQL DB. So far so good.
However, when I return to the initial screen, where it is, it ends up giving a problem. (There is already a% open% associated with this command that must be closed first.)
I’ve already tried and done what solved the third-party problem (create a second connection), but it did not work very well. Here is the method code:
public DataTable GetUF()
{
DataTable dataUf = new DataTable();
MySqlConnection bdConn = new MySqlConnection("Persist Security Info=False;server=localhost;database=controle;uid=root;pwd=''");
try
{
bdConn.Open();
if (bdConn2.State == ConnectionState.Open)
{
//Se estiver aberta faz a consulta dos dados do BD
MySqlCommand cmd = new MySqlCommand("SELECT identificador FROM computador WHERE status=0", bdConn);
cmd.BeginExecuteNonQuery();
dataUf.Load(cmd.ExecuteReader());
}
}
catch (Exception ex)
{
MessageBox.Show("Impossível estabelecer conexão.n" + ex.Message);
}
return dataUf;
}
Code of the ComboBox that is receiving the data:
public Form1()
{
InitializeComponent();
cbComputador.ValueMember = "identificador";
cbComputador.DisplayMember = "identificador";
cbComputador.DataSource = GetUF();
}
Note: I found this DataReader , but it did not help me much:
There is already an open DataReader associated with this command that should be closed first.
Answer :
The method Dispose() failed to call close the connection to the bank , actually every time you use an IDataReader needs to close shortly after its use and give the command Dispose() to free resources.
public DataTable GetUF()
{
DataTable dataUf = new DataTable();
MySqlConnection bdConn
= new MySqlConnection(
"Persist Security Info=False;server=localhost;database=controle;uid=root;pwd=''");
try
{
bdConn.Open();
if (bdConn2.State == ConnectionState.Open)
{
MySqlCommand cmd = new MySqlCommand(
"SELECT identificador FROM computador WHERE status=0", bdConn);
dataUf.Load(cmd.ExecuteReader());
cmd.Dispose();
}
bdConn.Close();
bdConn.Dispose();
}
catch (Exception ex)
{
MessageBox.Show("Impossível estabelecer conexão.n" + ex.Message);
}
return dataUf;
}
Note:
In the SQL Server 2005 and higher versions, there is a way to configure the connection to work with multiple IDataReader , which is to set up the MARS – Multiple Active Result Sets as follows: in% with connection add configuration:
MultipleActiveResultSets=True;
Example:
connectionString="Data Source=.SQLEXPRESS;" +
"Initial Catalog=Banco;Integrated Security=True;" +
"MultipleActiveResultSets=true;"
References