//method below are codes for connecting the database
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = "Provider = Microsoft.Jet.OLEDB.4.0";
+ "Data source= C:\Database\winbase.mdb";
return mDB;
}When i debug, i have a error saying unrecognized escape sequence. I tried adding @ and \\ but i have more errors.
Write the string as follows:
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; Data source= C:\Database\winbase.mdb";
return mDB;
}
This should work!or if you would like to have the string written in two (2) rows:
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; " +
@"Data source= C:\Database\winbase.mdb";
return mDB;
}
You get the error because C# considers the backslash character (\) and escape character to use to get a special characters (line return or linefeed). There are two ways to solve this problem, the first being the one Mitja posted, by prefixing the string with the "this is a literal string with no escape sequences" character (@) in front of the string. The second is to escape the escape character (use double \\). So these are equivalent:
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; Data source=C:\Database\winbase.mdb";
mDB.ConnectionString = "Provider = Microsoft.Jet.OLEDB.4.0; Data source=C:\\Database\\winbase.mdb";Hi. Thanks for replying.
I tried both ways and I got more errors.
this is my coding.
this is the one edited with the second way.
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace WineForUs
{
public class Stocks
{
OleDbCommand mDB = new OleDbCommand();
OleDbCommand cmd;
public int intQty;
//method below are codes for connecting the database
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; Data source=C:\Database\winbase.mdb";
return mDB;
}
//method below are codes to retrieve Product's quantity on hand
public Stocks(string strPName)
{
DbConnect(mDB);//this command calls DbConnect to activate the connection string
string strSQL = "Select QtyOnHand From Products Where ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Name", strPName);
// a try catch is used here to catch database errors
try
{
mDB.Open();
// the line below stores the QtyOnHand read by ExecuteScalar to oQty object
object oQty = cmd.ExecuteScalar();
intQty = (int)oQty;
mDB.Close();
return;
}
catch (Exception ex)
{
mDB.Close(); MessageBox.Show(ex.Message);
}
} // closing brace for Stocks(string strPName) method
// method below are codes to update Product's new quantity after a sale
public Stocks(string strPName, int intQty)
{
DbConnect(mDB);
String strSQL = "UPDATE Products SET QtyOnHand = @Qty WHERE ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Qty", intQty);
cmd.Parameters.AddWithValue("@Name", strPName);
try
{
mDB.Open();
cmd.ExecuteNonQuery();
mDB.Close();
MessageBox.Show("Stock quatity updated");
return;
}
catch (OleDbException e)
{
mDB.Close(); MessageBox.Show(e.Message);
}
}
}
}Hi. Thanks for replying.
I tried both ways and I got more errors.
this is my coding.
this is the one edited with the second way.
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace WineForUs
{
public class Stocks
{
OleDbCommand mDB = new OleDbCommand();
OleDbCommand cmd;
public int intQty;
//method below are codes for connecting the database
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; Data source=C:\Database\winbase.mdb";
return mDB;
}
//method below are codes to retrieve Product's quantity on hand
public Stocks(string strPName)
{
DbConnect(mDB);//this command calls DbConnect to activate the connection string
string strSQL = "Select QtyOnHand From Products Where ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Name", strPName);
// a try catch is used here to catch database errors
try
{
mDB.Open();
// the line below stores the QtyOnHand read by ExecuteScalar to oQty object
object oQty = cmd.ExecuteScalar();
intQty = (int)oQty;
mDB.Close();
return;
}
catch (Exception ex)
{
mDB.Close(); MessageBox.Show(ex.Message);
}
} // closing brace for Stocks(string strPName) method
// method below are codes to update Product's new quantity after a sale
public Stocks(string strPName, int intQty)
{
DbConnect(mDB);
String strSQL = "UPDATE Products SET QtyOnHand = @Qty WHERE ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Qty", intQty);
cmd.Parameters.AddWithValue("@Name", strPName);
try
{
mDB.Open();
cmd.ExecuteNonQuery();
mDB.Close();
MessageBox.Show("Stock quatity updated");
return;
}
catch (OleDbException e)
{
mDB.Close(); MessageBox.Show(e.Message);
}
}
}
}Which lines give you errors, and what errors are they? You need to give us as much information as possible.
okay. this is my codes.
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace WineForUs
{
public class Stocks
{
OleDbCommand mDB = new OleDbCommand();
OleDbCommand cmd;
public int intQty;
//method below are codes for connecting the database
private static OleDbCommand DbConnect(OleDbCommand mDB)
{
mDB.ConnectionString = @"Provider = Microsoft.Jet.OLEDB.4.0; Data source=C:\Database\winbase.mdb";
return mDB;
}
//method below are codes to retrieve Product's quantity on hand
public Stocks(string strPName)
{
DbConnect(mDB);//this command calls DbConnect to activate the connection string
string strSQL = "Select QtyOnHand From Products Where ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Name", strPName);
// a try catch is used here to catch database errors
try
{
mDB.Open();
// the line below stores the QtyOnHand read by ExecuteScalar to oQty object
object oQty = cmd.ExecuteScalar();
intQty = (int)oQty;
mDB.Close();
return;
}
catch (Exception ex)
{
mDB.Close(); MessageBox.Show(ex.Message);
}
} // closing brace for Stocks(string strPName) method
// method below are codes to update Product's new quantity after a sale
public Stocks(string strPName, int intQty)
{
DbConnect(mDB);
String strSQL = "UPDATE Products SET QtyOnHand = @Qty WHERE ProductName = @Name";
cmd = new OleDbCommand(strSQL, mDB);
cmd.Parameters.AddWithValue("@Qty", intQty);
cmd.Parameters.AddWithValue("@Name", strPName);
try
{
mDB.Open();
cmd.ExecuteNonQuery();
mDB.Close();
MessageBox.Show("Stock quatity updated");
return;
}
catch (OleDbException e)
{
mDB.Close(); MessageBox.Show(e.Message);
}
} //closing brace for stocks(string strPName, int intQty) method
} // closing brace for class
}// closing brace for namespacethere are 5 errors.
1. 'System.Data.OleDb.OleDbCommand' does not contain a definition for 'Close' and no extension method 'Close' accepting a first argument of type 'System.Data.OleDb.OleDbCommand' cound be found.
Line 35 Column 21, Line 40 Column 21, Line 55 Column 21, Line 61 Column 21.
2. 'System.Data.OleDb.OleDbCommand' does not contain a definition for 'ConnectionString' and no extension method 'ConnectionString' accepting a first argument of type 'System.Data.OleDb.OleDbCommand' cound be found.
Line 18 Column 17
3. 'System.Data.OleDb.OleDbCommand' does not contain a definition for 'Open' and no extension method 'Open' accepting a first argument of type 'System.Data.OleDb.OleDbCommand' cound be found.
Line 31 Column 21, Line 53 Column 21
4.Argument'2' : cannot convert from 'System.Data.OleDb.OleDbCommand'to 'System.Data.OleDb.OleDbConnection'
Line 26 Column 44, Line 48 Column 44
5. The best overloaded method match for 'System.Data.OleDb.OleDbCommand.OleDbCommand(string,System.Data.OleDb.OleDbConnection)' has some invalid arguments.
Line 26 Column 19, Line 48 Column 19
These errors has nothing to do with the connection string to your database. Your code is a bit weird.
Do you use "using" statement while accessing to db?
like this:
try
{
using (SqlConnection sqlConn = new SqlConnection( connectionString ) )
{
//query string and opening the connetion
sqlConn.Open();
}
}
catch ( Exception )
{
//catch errors
}
finally
{
//closing connection
}Example:
private static void CreateCommand(string queryString, string connectionString)
{
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
command.Connection.Open();
command.ExecuteNonQuery();
}
}This is the best approach, I would say.
To ensure that connections are always closed, open the connection inside of a using block, as shown in the following code fragment. Doing so ensures that the connection is automatically closed when the code exits the block.
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