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

最新推荐文章于 2012-11-20 11:03:44 发布

原创最新推荐文章于 2012-11-20 11:03:44 发布 · 1.4k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#c# #microsoft #dataset #sql server #button #permissions

程序之路专栏收录该内容

30 篇文章

订阅专栏

博客围绕C#项目展开，提及了相关要求及项目创建过程，还涉及SQL Server的应用，可能与数据处理等信息技术相关内容有关。

SUMMARY

The GetChunk and the AppendChunk methods are not available in ADO.NET on DataReader columns, DataSet columns, or Command parameters. This article describes how to use Visual C# .NET to read and write binary large object (BLOB) fields.

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

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 C# Windows Application project.

3. Drag two Button controls from the toolbox 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).

Add the following code to the top of the Code window:

using System.Data;
using System.Data.SqlClient;
using System.IO;

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

Note Uid <user name> must have permissions to perform these operations on the database.

{
SqlConnection con = new SqlConnection("Server=Darkover;uid=<username>;pwd=<strong password>;database=northwind");
SqlDataAdapter da = new SqlDataAdapter("Select * From MyImages", con);
SqlCommandBuilder MyCB = new SqlCommandBuilder(da);
DataSet ds = new DataSet("MyImages");

da.MissingSchemaAction = MissingSchemaAction.AddWithKey;
FileStream fs = new FileStream(@"C:/winnt/Gone Fishing.BMP", FileMode.OpenOrCreate, FileAccess.Read);

byte[] MyData= new byte[fs.Length];
fs.Read(MyData, 0, System.Convert.ToInt32(fs.Length));

fs.Close();

da.Fill(ds,"MyImages");

DataRow myRow;
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");

con.Close();

}

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

Note Uid <user name> must have permissions to perform these operations on the database.

{
SqlConnection con = new SqlConnection("Server=Darkover;uid=<username>;pwd=<strong password>;database=northwind");
SqlDataAdapter da = new SqlDataAdapter("Select * From MyImages", con);
SqlCommandBuilder MyCB = new SqlCommandBuilder(da);
DataSet ds = new DataSet("MyImages");

byte[] MyData= new byte[0];

da.Fill(ds, "MyImages");
DataRow myRow;
myRow=ds.Tables["MyImages"].Rows[0];

MyData =  (byte[])myRow["imgField"];
int ArraySize = new int();
ArraySize = MyData.GetUpperBound(0);

FileStream fs = new FileStream(@"C:/winnt/Gone Fishing2.BMP", FileMode.OpenOrCreate, FileAccess.Write);
fs.Write(MyData, 0,ArraySize);
fs.Close();
}

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.

10. Click Save to File (from Database) to save the data from the SQL Server Image field back to a file.