How To Read and Write BLOB Data by Using ADO.NET with Visual Basic .NET

For a Microsoft Visual C# .NET version of this article, see
309158 .
This article refers to the following Microsoft .NET Framework Class Library namespaces:
  • System.Data.SqlClient
  • System.IO

IN THIS TASK

Summary

The GetChunk and the AppendChunk methods are not available in ADO.NET to read and write binary large object (BLOB) fields. This article describes how to use the FileStream object and a byte array to read and to write BLOB data from Microsoft SQL Server to a file.

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

Create the Project

  1. Add a table named MyImages to your SQL Server Northwind database. Include the following fields in your table:
    • Identity field that is named "ID" of type Int.
    • Field that is named "Description" of type VarChar with a length of 50.
    • Field that is named "ImgField" of type Image.

  2. Start Visual Studio .NET, and then create a new Visual Basic Windows Application project.
  3. Add two Button controls to the default form, Form1.
  4. In the Properties window, change the Text property of Button1 to Save to Database (from File), and then change the Text property of Button2 to Save to File (from Database).
  5. Add the following code to the top of the Code window:
          Imports System.Data.SqlClient
    Imports System.IO
  6. Double-click Button1, and then add the following code to the Button1_Click event handler:
    Note You must change uid<username> and pwd =<strong password> to the correct values before you run this code. Make sure that User ID has the appropriate permissions to perform this operation on the database.
          Dim con As New SqlConnection _
    ("Server=YourServer;uid=<username>;pwd=<strong password>;database=northwind")
    Dim da As New SqlDataAdapter _
    ("Select * From MyImages", con)
    Dim MyCB As SqlCommandBuilder = New SqlCommandBuilder(da)
    Dim ds As New DataSet()

    da.MissingSchemaAction = MissingSchemaAction.AddWithKey

    Dim fs As New FileStream _
    ("C:\winnt\Gone Fishing.BMP", FileMode.OpenOrCreate, _
    FileAccess.Read)
    Dim MyData(fs.Length) As Byte
    fs.Read(MyData, 0, fs.Length)
    fs.Close()
    con.Open()
    da.Fill(ds, "MyImages")
    Dim myRow As DataRow
    myRow = ds.Tables("MyImages").NewRow()

    myRow("Description") = "This would be description text"
    myRow("imgField") = MyData
    ds.Tables("MyImages").Rows.Add(myRow)
    da.Update(ds, "MyImages")

    fs = Nothing
    MyCB = Nothing
    ds = Nothing
    da = Nothing

    con.Close()
    con = Nothing
    MsgBox ("Image saved to database")
  7. Double-click Button2, and then add the following code to the Button2_Click event handler:
    Note You must change uid <username> and pwd =<strong password> to the correct values before you run this code. Make sure that User ID has the appropriate permissions to perform this operation on the database.
          Dim con As New SqlConnection _
    ("Server=YourServer;uid=<username>;pwd=<strong password>;database=northwind")
    Dim da As New SqlDataAdapter _
    ("Select * From MyImages", con)
    Dim MyCB As SqlCommandBuilder = New SqlCommandBuilder(da)
    Dim ds As New DataSet()

    con.Open()
    da.Fill(ds, "MyImages")
    Dim myRow As DataRow
    myRow = ds.Tables("MyImages").Rows(0)

    Dim MyData() As Byte
    MyData = myRow("imgField")
    Dim K As Long
    K = UBound(MyData)

    Dim fs As New FileStream _
    ("C:\winnt\Gone Fishing2.BMP", FileMode.OpenOrCreate, _
    FileAccess.Write)
    fs.Write(MyData, 0, K)
    fs.Close()

    fs = Nothing
    MyCB = Nothing
    ds = Nothing
    da = Nothing

    con.Close()
    con = Nothing
    MsgBox ("Image retrieved")
  8. Press F5 to compile and to run the application.
  9. Click Save to Database (from File) to load the image, C:\WinNT\Gone Fishing.bmp, into the SQL Server Image field. After you receive the confirmation message that the image has been saved, check your table to verify.
  10. Click Save to File (from Database) to save the data from the SQL Server Image field back to a file. Verify that C:\WinNT\Gone Fishing2.bmp now exists.

References

For additional information about a similar topic in Visual Basic 6.0, click the following article number to view the article in the Microsoft Knowledge Base:
258038 How To Access and Modify SQL Server BLOB Data by Using the ADO Stream Object
Properties

Article ID: 308042 - Last Review: Oct 16, 2012 - Revision: 1

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