Why Does \'DataReader Must Be Closed First\' Occur, and How Can I Resolve It?

Data Management Exception: Understanding and Resolving "DataReader Must Be Closed First" Error

In the provided code, you attempt to execute a new SQL statement using ExecuteNonQuery() while a DataReader is still open for the same connection. This raises the exception, "There is already an open DataReader associated with this Connection which must be closed first."

According to MSDN, this exception occurs because when a DataReader is open, the connection it uses is locked exclusively for the duration of its usage. This means no other commands, including creating a new DataReader, can be executed for that connection until the original DataReader is closed.

To resolve this error, you should ensure that the DataReader is closed before attempting to execute any other commands on the same connection. In the provided code, this can be achieved by adding a call to myReader.Close() immediately before the line that throws the exception:

myCommand.Dispose();
myReader.Close(); // Close DataReader
if (myReader.HasRows) {
    int i = 0;
    // Always call Read before accessing data.
    while (myReader.Read()) {
        if (myReader["frProductid"].ToString() == "") //there is no productid exist for this item
        {
            strInsertSQL = "Insert Into tblProduct_temp (Productid) Values('this istest') ";
            MySqlCommand cmdInserttblProductFrance = new MySqlCommand(strInsertSQL, myConnection);
            cmdInserttblProductFrance.ExecuteNonQuery(); // ExecuteNonQuery after closing DataReader
        }
    }
}

By closing the DataReader before executing the ExecuteNonQuery() command, you release the exclusive lock on the connection and allow the new command to execute successfully.

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