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Passing a DataReader between methods and getting RETURN_VALUE

P: n/a
Hi all,

I have the following problem:

I have a private method that returns a SqlDataReader. For this to work I
have not to close the DB connection in the above method. I do this only to
have the possibility to iterate through the entire rows set in a while loop,
located in the calling method.

I have included a few lines of code to get the number of rows fetched from
the DB. I do this with SqlParameter("RETURN_VALUE", SqlDbType.Int) [ I am
using a stored procedure that return @@rowcount].

I have found out that I am getting the appropriate value for the stored
procedure parameter ("RETURN_VALUE") ONLY when I have explicitly close the
DB connection. Unfortunately when the control is returned to the calling
method the usual error message

Invalid attempt to Read when reader is closed

is being received as the connection is closed and there's no such DataReader
already.

Does anyone know a workaround for this?

Thanks,

Martin

------------------------

private SqlDataReader GetReader(string parameter, string date)

{

DateTime MyDateTime;

.....//. date parsing
SqlConnection myConn = new SqlConnection(ConnectionString());
SqlCommand myCmd = new SqlCommand();

SqlDataReader myReader=null;

myCmd.CommandType = CommandType.StoredProcedure;
myCmd.Connection = myConn;
myCmd.CommandText = "GetData";
myCmd.CommandTimeout = 250;

SqlParameter Param1 = new SqlParameter();
Param1 = myCmd.Parameters.Add("@parameter", SqlDbType.VarChar, 12);
Param1.Direction = ParameterDirection.Input;
Param1.Value = parameter;

SqlParameter Param2 = new SqlParameter();
Param2 = myCmd.Parameters.Add("@date", SqlDbType.VarChar, 20);
Param2.Direction = ParameterDirection.Input;
Param2.Value = MyDateTime.Date.ToShortDateString();
SqlParameter outValue = new SqlParameter();
outValue = myCmd.Parameters.Add("RETURN_VALUE", SqlDbType.Int);
outValue.Direction = ParameterDirection.ReturnValue;

myConn.Open();
myReader = myCmd.ExecuteReader();

// this works only is myConn.Close() is executed but then

// we cannot return a READER to the calling method???

intRowsReturned =
Convert.ToInt32(myCmd.Parameters["RETURN_VALUE"].Value);
return myReader;
}

// the calling method

private void btnSQLGet_Click(object sender, System.EventArgs e)

{

/// ... .

// get the data in a reader

SqlDataReader myReader = GetReader(cboParameter.Text, txtDate.Text);
if (myReader==null)
return;
///.....

}

Nov 18 '05 #1
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2 Replies


P: n/a
You can't read output parameters in a DataReader until the DataReader is
closed. Close the DataReader, and leave the Connection opened to read the
value.

--
HTH,
Kevin Spencer
..Net Developer
Microsoft MVP
Big things are made up
of lots of little things.

"Martin Raychev" <ma*******@hotmail.com> wrote in message
news:#R**************@TK2MSFTNGP09.phx.gbl...
Hi all,

I have the following problem:

I have a private method that returns a SqlDataReader. For this to work I
have not to close the DB connection in the above method. I do this only to
have the possibility to iterate through the entire rows set in a while loop, located in the calling method.

I have included a few lines of code to get the number of rows fetched from
the DB. I do this with SqlParameter("RETURN_VALUE", SqlDbType.Int) [ I am
using a stored procedure that return @@rowcount].

I have found out that I am getting the appropriate value for the stored
procedure parameter ("RETURN_VALUE") ONLY when I have explicitly close the
DB connection. Unfortunately when the control is returned to the calling
method the usual error message

Invalid attempt to Read when reader is closed

is being received as the connection is closed and there's no such DataReader already.

Does anyone know a workaround for this?

Thanks,

Martin

------------------------

private SqlDataReader GetReader(string parameter, string date)

{

DateTime MyDateTime;

.....//. date parsing
SqlConnection myConn = new SqlConnection(ConnectionString());
SqlCommand myCmd = new SqlCommand();

SqlDataReader myReader=null;

myCmd.CommandType = CommandType.StoredProcedure;
myCmd.Connection = myConn;
myCmd.CommandText = "GetData";
myCmd.CommandTimeout = 250;

SqlParameter Param1 = new SqlParameter();
Param1 = myCmd.Parameters.Add("@parameter", SqlDbType.VarChar, 12);
Param1.Direction = ParameterDirection.Input;
Param1.Value = parameter;

SqlParameter Param2 = new SqlParameter();
Param2 = myCmd.Parameters.Add("@date", SqlDbType.VarChar, 20);
Param2.Direction = ParameterDirection.Input;
Param2.Value = MyDateTime.Date.ToShortDateString();
SqlParameter outValue = new SqlParameter();
outValue = myCmd.Parameters.Add("RETURN_VALUE", SqlDbType.Int);
outValue.Direction = ParameterDirection.ReturnValue;

myConn.Open();
myReader = myCmd.ExecuteReader();

// this works only is myConn.Close() is executed but then

// we cannot return a READER to the calling method???

intRowsReturned =
Convert.ToInt32(myCmd.Parameters["RETURN_VALUE"].Value);
return myReader;
}

// the calling method

private void btnSQLGet_Click(object sender, System.EventArgs e)

{

/// ... .

// get the data in a reader

SqlDataReader myReader = GetReader(cboParameter.Text, txtDate.Text);
if (myReader==null)
return;
///.....

}

Nov 18 '05 #2

P: n/a
1) the return value and parameters values of a stored proc are returned
after all result sets in the proc are returned.
2) a datareader is a forward only cursor, so to get to the return value, you
need to read thru all rows, and result sets
3) a close will read thru all rows and result sets for you, but is not
necessary, the following code will also work:

// process all result sets to get to parameters and reutn value

do
{
while (dr.Read())
;
} while (dr.NextResult())

// now you can access output parameters and the return value

returning a row count makes little sesnse, as you could add up the row
count yourself, as you have to read them all to get to the count return
value.

-- bruce (sqlwork.com)
"Martin Raychev" <ma*******@hotmail.com> wrote in message
news:#R**************@TK2MSFTNGP09.phx.gbl...
Hi all,

I have the following problem:

I have a private method that returns a SqlDataReader. For this to work I
have not to close the DB connection in the above method. I do this only to
have the possibility to iterate through the entire rows set in a while loop, located in the calling method.

I have included a few lines of code to get the number of rows fetched from
the DB. I do this with SqlParameter("RETURN_VALUE", SqlDbType.Int) [ I am
using a stored procedure that return @@rowcount].

I have found out that I am getting the appropriate value for the stored
procedure parameter ("RETURN_VALUE") ONLY when I have explicitly close the
DB connection. Unfortunately when the control is returned to the calling
method the usual error message

Invalid attempt to Read when reader is closed

is being received as the connection is closed and there's no such DataReader already.

Does anyone know a workaround for this?

Thanks,

Martin

------------------------

private SqlDataReader GetReader(string parameter, string date)

{

DateTime MyDateTime;

.....//. date parsing
SqlConnection myConn = new SqlConnection(ConnectionString());
SqlCommand myCmd = new SqlCommand();

SqlDataReader myReader=null;

myCmd.CommandType = CommandType.StoredProcedure;
myCmd.Connection = myConn;
myCmd.CommandText = "GetData";
myCmd.CommandTimeout = 250;

SqlParameter Param1 = new SqlParameter();
Param1 = myCmd.Parameters.Add("@parameter", SqlDbType.VarChar, 12);
Param1.Direction = ParameterDirection.Input;
Param1.Value = parameter;

SqlParameter Param2 = new SqlParameter();
Param2 = myCmd.Parameters.Add("@date", SqlDbType.VarChar, 20);
Param2.Direction = ParameterDirection.Input;
Param2.Value = MyDateTime.Date.ToShortDateString();
SqlParameter outValue = new SqlParameter();
outValue = myCmd.Parameters.Add("RETURN_VALUE", SqlDbType.Int);
outValue.Direction = ParameterDirection.ReturnValue;

myConn.Open();
myReader = myCmd.ExecuteReader();

// this works only is myConn.Close() is executed but then

// we cannot return a READER to the calling method???

intRowsReturned =
Convert.ToInt32(myCmd.Parameters["RETURN_VALUE"].Value);
return myReader;
}

// the calling method

private void btnSQLGet_Click(object sender, System.EventArgs e)

{

/// ... .

// get the data in a reader

SqlDataReader myReader = GetReader(cboParameter.Text, txtDate.Text);
if (myReader==null)
return;
///.....

}

Nov 18 '05 #3

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