How To Access and Modify SQL Server BLOB Data by Using the ADO Stream Object (258038)

MORE INFORMATION

The following code samples are based on the data stored in the pub_info table in the SQL Server 7.0 pubs sample database. You need to modify the ADO connection string to point to your SQL Server installation.

Example 1 : Saving the Data in a SQL Server Image Column to a File on the Hard Disk

The code in this example opens a recordset on the pub_info table in the pubs database and saves the binary image data stored in the logo column of the first record to a file on the hard disk, as follows:

1. Open a new Standard EXE Visual Basic project.
2. On the Project menu, click to select References, and then set a reference to the Microsoft ActiveX Data Objects 2.5 Object Library.
3. Place a CommandButton control on Form1.
4. Make the following declarations in the form's General declarations section:

   Dim cn As ADODB.Connection
   Dim rs As ADODB.Recordset
   Dim mstream As ADODB.Stream
   					

5. Cut and paste the following code into the Click event of the CommandButton that you added to the form:

   Set cn = New ADODB.Connection
   cn.Open "Provider=SQLOLEDB;data Source=<name of your SQL Server>;
   Initial Catalog=pubs;User Id=<Your Userid>;Password=<Your Password>"
   
   Set rs = New ADODB.Recordset
   rs.Open "Select * from pub_info", cn, adOpenKeyset, adLockOptimistic
   
   Set mstream = New ADODB.Stream
   mstream.Type = adTypeBinary
   mstream.Open
   mstream.Write rs.Fields("logo").Value
   mstream.SaveToFile "c:\publogo.gif", adSaveCreateOverWrite
   
   rs.Close
   cn.Close
   					

6. Save and run the Visual Basic project.
7. Click the CommandButton to save the binary data in the logo column of the first record to the file c:\publogo.gid. Look for this file in Windows Explorer and open it to view the saved image.
   
   The code in this example declares an ADODB Stream object and sets its Type property to adTypeBinary to reflect that this object will be used to work with Binary data. Following this, the binary data stored in the logo column of the first record in the pub_info table is written out to the Stream object by calling its Write method. The Stream object now contains the binary data that is saved to the file by calling its SaveToFile method and passing in the path to the file. The adSaveCreateOverWrite constant passed in as the second parameter causes the SaveToFile method to overwrite the specified file if it already exists.

Example 2 : Transfer the Image Stored in a .gif File to an Image Column in a SQL Server Table

The code in this example saves an image stored in a .gif file to the logo column in the first record of the pub_info table by overwriting its current contents, as follows:

1. Open a new Standard EXE Visual Basic project.
2. On the Project menu, click to select References, and then set a reference to the Microsoft ActiveX Data Objects 2.5 Object Library.
3. Place a CommandButton on Form1.
4. Make the following declarations in the form's General declarations section:

   Dim cn As ADODB.Connection
   Dim rs As ADODB.Recordset
   Dim mstream As ADODB.Stream
   					

5. Cut and paste the following code in the Click event of the CommandButton that you added to the form:

   Set cn = New ADODB.Connection
   cn.Open "Provider=SQLOLEDB;data Source=<name of your SQL Server>;
   Initial Catalog=pubs;User Id=<Your Userid>;Password=<Your Password>"
   
   Set rs = New ADODB.Recordset
   rs.Open "Select * from pub_info", cn, adOpenKeyset, adLockOptimistic
   
   Set mstream = New ADODB.Stream
   mstream.Type = adTypeBinary
   mstream.Open
   mstream.LoadFromFile "<path to .gif file>"
   rs.Fields("logo").Value = mstream.Read
   rs.Update
   
   rs.Close
   cn.Close
   					

6. Save and run the Visual Basic project.
7. Click on the CommandButton to run the code to stream the contents of the .gif file to the ADO Stream object, and save the data in the Stream to the logo column in the first record of the recordset.
8. Verify that the image in the logo column has been modified by using the code in Example 1.