vb.net qr code generator free Figure 9-3. Accessing Northwind via the SQL Server data provider in VB.NET

Drawer Data Matrix 2d barcode in VB.NET Figure 9-3. Accessing Northwind via the SQL Server data provider

Figure 9-3. Accessing Northwind via the SQL Server data provider
DataMatrix Drawer In VB.NET
Using Barcode creation for VS .NET Control to generate, create Data Matrix ECC200 image in .NET framework applications.
www.OnBarcode.com
Reading Data Matrix ECC200 In VB.NET
Using Barcode recognizer for .NET framework Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
CHAPTER 9 s GETTING TO KNOW ADO.NET
EAN13 Creator In VB.NET
Using Barcode creator for .NET framework Control to generate, create EAN 13 image in .NET applications.
www.OnBarcode.com
Data Matrix 2d Barcode Printer In Visual Basic .NET
Using Barcode drawer for .NET framework Control to generate, create Data Matrix ECC200 image in VS .NET applications.
www.OnBarcode.com
How It Works
Code 128 Code Set A Drawer In Visual Basic .NET
Using Barcode maker for VS .NET Control to generate, create Code128 image in Visual Studio .NET applications.
www.OnBarcode.com
Barcode Maker In VB.NET
Using Barcode generation for VS .NET Control to generate, create Barcode image in VS .NET applications.
www.OnBarcode.com
Let s take a look at how the code works, starting with the using directives: Imports System Imports System.Data Imports System.Data.SqlClient The reference to System.Data is not needed in this small program, since you don t explicitly use any of its members, but it s a good habit to always include it. The reference to System. Data.SqlClient is necessary since you want to use the simple names of its members. You specify the connection string with parameters (key-value pairs) suitable for a SQL Server Express session: 'Set up connection string Dim conn As New SqlConnection conn.ConnectionString = "Data Source=.\sqlexpress;" & _ "Initial Catalog=Northwind;Integrated Security=True" The connection string contains this parameter: Integrated Security=True which specifies Windows Authentication, so any user logged on to Windows can access the SQLEXPRESS instance. You then code the SQL query: 'Set up query string Dim sql As String = "select * from employees" You next declare variables for data reader, so that becomes available to the rest of your code: 'Declare data reader variables Dim reader As SqlDataReader = Nothing You then create the connection and open it: Try ' Open connection conn.Open() You do this (and the rest of your database work) in a try block to handle exceptions, in particular exceptions thrown by ADO.NET in response to database errors. Here, ADO.NET will throw an exception if the connection string parameters aren t syntactically correct, so you may as well be prepared. If you had waited until you entered the try block to declare the connection (and data reader) variable, you wouldn t have it available in the finally block to close the connection. Note that creating a connection doesn t actually connect to the database. You need to call the Open method on the connection. To execute the query, you first create a command object, passing its constructor the SQL to run and the connection on which to run it. Next, you create a data reader by calling ExecuteReader() on the command object. This not only executes the query, but also sets up
Barcode Drawer In VB.NET
Using Barcode creator for VS .NET Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
ISSN - 10 Drawer In Visual Basic .NET
Using Barcode generation for Visual Studio .NET Control to generate, create ISSN image in Visual Studio .NET applications.
www.OnBarcode.com
CHAPTER 9 s GETTING TO KNOW ADO.NET
Generating Data Matrix In Java
Using Barcode maker for Java Control to generate, create DataMatrix image in Java applications.
www.OnBarcode.com
Decoding DataMatrix In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
the data reader. Note that unlike with most objects, you have no way to create a data reader with a new expression. ' Execute the query Dim cmd As New SqlCommand(sql, conn) reader = cmd.ExecuteReader() You then produce a header for your output, using connection and command properties (Database and CommandText, respectively) to get the database name and query text: ' Display output header Console.WriteLine("This program demonstrates the use of " & _ "the SQL Server Data Provider.") Console.WriteLine("Querying database {0} with query {1}" & _ ControlChars.NewLine, conn.Database, cmd.CommandText) Console.WriteLine("First Name" + ControlChars.Tab & _ "Last Name" + ControlChars.Lf) You retrieve all the rows in the result set by calling the data reader s Read method, which returns true if there are more rows and false otherwise. Note that the data reader is positioned immediately before the first row prior to the first call to Read: ' Process the result set While reader.Read() Console.WriteLine("{0} | {1}", _ reader("FirstName").ToString().PadLeft(10), _ reader(1).ToString().PadLeft(10)) End While You access each row s columns with the data reader s indexer (here, the SqlDataReader. Item property), which is overloaded to accept either a column name or a zero-based integer index. You use both so you can see the indexer s use, but using column numbers is more efficient than using column names. Next you handle any exceptions, quite simplistically, but at least you re developing a good habit. We ll cover exception handling much more thoroughly in 16. Catch e As Exception Console.WriteLine("Error: ", e) At last, in a finally block, you close the data reader and the connection by calling their Close methods. As a general rule, you should close things in a finally block to be sure they get closed no matter what happens within the try block. Finally ' Close reader and connection reader.Close() conn.Close() End Try Technically, closing the connection also closes the data reader, but closing both (in the previous order) is another good habit. A connection with an open data reader can t be used for any other purpose until the data reader has been closed.
Recognize QR Code ISO/IEC18004 In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
UPC-A Supplement 2 Scanner In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Code 128B Printer In None
Using Barcode maker for Microsoft Excel Control to generate, create Code 128 Code Set A image in Excel applications.
www.OnBarcode.com
2D Barcode Printer In .NET Framework
Using Barcode generation for .NET framework Control to generate, create Matrix 2D Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
EAN13 Creator In VS .NET
Using Barcode maker for ASP.NET Control to generate, create GTIN - 13 image in ASP.NET applications.
www.OnBarcode.com
UPC Code Creator In None
Using Barcode drawer for Microsoft Excel Control to generate, create GS1 - 12 image in Microsoft Excel applications.
www.OnBarcode.com
Barcode Printer In Objective-C
Using Barcode printer for iPad Control to generate, create Barcode image in iPad applications.
www.OnBarcode.com
ECC200 Drawer In VS .NET
Using Barcode generator for ASP.NET Control to generate, create Data Matrix 2d barcode image in ASP.NET applications.
www.OnBarcode.com
USS Code 128 Decoder In Visual Studio .NET
Using Barcode reader for .NET framework Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Encode Code 3/9 In Java
Using Barcode printer for Eclipse BIRT Control to generate, create Code 39 image in BIRT applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.