HOW TO: Read and Write BLOB Data by Using ADO.NET Through ASP.NET (326502)

SUMMARY

This article describes how to use the FileStream object and a byte array in ASP.NET to write binary large object (BLOB) data to Microsoft SQL Server. This article also describes how to load BLOB data from the SQL Server database and how to copy this data to a downloadable file through the .aspx page.

back to the top

Requirements

The following list outlines the recommended hardware, software, network infrastructure, and service packs that are required:

• Microsoft Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server, or Windows NT 4.0 Server
• Microsoft Visual Studio .NET
• Microsoft SQL Server

back to the top

Create the Project

This sample project connects to the SQL Server Pubs database. This project uses the existing Pub_info table and stores a .jpg file in the logo field of this table. The data type of the logo field is Image.

1. To create a new ASP.NET Web Application project in Microsoft Visual Basic .NET, follow these steps:
   1. Start Visual Studio .NET.
   2. On the File menu, point to New, and then click Project.
   3. In the New Project dialog box, click Visual Basic Projects under Project Types, and then click ASP.NET Web Application under Templates.
2. Drag two Button controls from the Web Forms section of the toolbox to the default Web form.
3. In the Properties window, change the Text property of Button1 to Save File to Database, and then change the Text property of Button2 to Load File from Database.
4. Add the following code to the top of the code-behind window:

         Imports System.Data.SqlClient
         Imports System.IO
   					

5. Double-click Button1, and then add the following code to the Button1_Click event handler:

           Dim con As New SqlConnection("Server=yileiw2;uid=sqlauth;pwd=sqlauth;database=pubs")
           Dim da As New SqlDataAdapter("Select * From pub_info", con)
           Dim MyCB As SqlCommandBuilder = New SqlCommandBuilder(da)
           Dim ds As New DataSet()
   
           da.MissingSchemaAction = MissingSchemaAction.AddWithKey
           con.Open()
           da.Fill(ds, "Pub_info")
   
           Dim fs As New FileStream _
            ("C:\SomePath\MyPhoto.jpg", FileMode.OpenOrCreate, _
             FileAccess.Read)
           Dim MyData(fs.Length) As Byte
           fs.Read(MyData, 0, fs.Length)
           fs.Close()
           ds.Tables("Pub_info").Rows(0)("logo") = MyData
           da.Update(ds, "Pub_info")
   
           fs = Nothing
           MyCB = Nothing
           ds = Nothing
           da = Nothing
   
           con.Close()
           con = Nothing
           Response.Write("File saved to database")
   					

6. Double-click Button2, and then add the following code to the Button2_Click event handler:

           Dim con As New SqlConnection("Server=yileiw2;uid=sqlauth;pwd=sqlauth;database=pubs")
           Dim da As New SqlDataAdapter("Select * From pub_info", con)
           Dim MyCB As SqlCommandBuilder = New SqlCommandBuilder(da)
           Dim ds As New DataSet()
   
           con.Open()
           da.Fill(ds, "Pub_info")
           Dim myRow As DataRow
           myRow = ds.Tables("Pub_info").Rows(0)
   
           Dim MyData() As Byte
           MyData = myRow("logo")
           
           Response.Buffer = True
           Response.ContentType = "Image/JPEG"
           Response.BinaryWrite(MyData)
   
           MyCB = Nothing
           ds = Nothing
           da = Nothing
   
           con.Close()
           con = Nothing
   					

7. Press F5 to compile and to run the application.
8. Click Save File to Database to save MyPhoto.jpg in the SQL Server Image field. After you receive the confirmation message that the image has been saved, check your table to verify.
9. Click Load File from Database to load the data from the SQL Server Image field to the Web browser.

back to the top

Additional Information

Although this sample uses a .jpg file, you can download any type of file from your Web application to the client browser. For example, to use a Microsoft Word document instead of a .jpg file, replace the following code

Response.ContentType = "Image/JPEG"
				

with this code:

Response.AddHeader("Content-Disposition", "attachment;filename=blob.doc")
Response.ContentType = "application/msword"
				

For a list of other content types and the code that is associated with each content type, visit the following AspTutorial.info Web site: back to the top