通过ADO.NET存取文件

时我们需要把一些大的数据对象如图片、可执行文件、视频和文档等数据存入数据库。在MS SQL Server中，这要用到Image数据类型，可以保存多达2G的数据。以下给出一个通过ADO.NET和MS SQL Server实现的小小的例子。

先创建一个测试数据表。
在查询分析器中输入并执行以下语句：
Create table [imgtable](
[imgid] [int] IDENTITY(1,1) NOT NULL,
[imgname] [varchar](100) COLLATE Chinese_PRC_CI_AS NULL,
[imgData] [image] NULL,
PRIMARY KEY CLUSTERED
(
[imgid]
) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

这要在你所选的数据库中就多了一个名叫imgtable的表。

VS中的代码如下：
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient;
using System.IO;

namespace ADO_Demo
{
/// <summary>
/// Form1 的摘要说明。
/// </summary>
public class ADO_Demo : System.Windows.Forms.Form
{
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Button button2;
private System.Windows.Forms.PictureBox pictureBox1;
private System.Windows.Forms.OpenFileDialog openFileDialog1;
private System.Windows.Forms.Button button3;
/// <summary>
/// 必需的设计器变量。
/// </summary>
private System.ComponentModel.Container components = null;

public ADO_Demo()
{
//
// Windows 窗体设计器支持所必需的
//
InitializeComponent();

//
// TOD 在 InitializeComponent 调用后添加任何构造函数代码
//
}

/// <summary>
/// 清理所有正在使用的资源。
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows 窗体设计器生成的代码
/// <summary>
/// 设计器支持所需的方法 – 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.button2 = new System.Windows.Forms.Button();
this.pictureBox1 = new System.Windows.Forms.PictureBox();
this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
this.button3 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(368, 48);
this.button1.Name = “button1″;
this.button1.Size = new System.Drawing.Size(104, 23);
this.button1.TabIndex = 0;
this.button1.Text = “保存图片”;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// button2
//
this.button2.Location = new System.Drawing.Point(368, 120);
this.button2.Name = “button2″;
this.button2.Size = new System.Drawing.Size(104, 23);
this.button2.TabIndex = 1;
this.button2.Text = “显示图片”;
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// pictureBox1
//
this.pictureBox1.Location = new System.Drawing.Point(8, 16);
this.pictureBox1.Name = “pictureBox1″;
this.pictureBox1.Size = new System.Drawing.Size(312, 288);
this.pictureBox1.TabIndex = 2;
this.pictureBox1.TabStop = false;
//
// openFileDialog1
//
this.openFileDialog1.FileOk += new System.ComponentModel.CancelEventHandler(this.openFileDialog1_FileOk);
//
// button3
//
this.button3.Location = new System.Drawing.Point(368, 200);
this.button3.Name = “button3″;
this.button3.Size = new System.Drawing.Size(104, 23);
this.button3.TabIndex = 1;
this.button3.Text = “读取文件并打开”;
this.button3.Click += new System.EventHandler(this.button3_Click);
//
// ADO_Demo
//
this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
this.ClientSize = new System.Drawing.Size(496, 317);
this.Controls.Add(this.pictureBox1);
this.Controls.Add(this.button2);
this.Controls.Add(this.button1);
this.Controls.Add(this.button3);
this.Name = “ADO_Demo”;
this.Text = “ADO_Demo”;
this.ResumeLayout(false);

}
#endregion

/// <summary>
/// 应用程序的主入口点。
/// </summary>
[STAThread]
static void Main()
{
Application.Run(new ADO_Demo());
}

/// <summary>
/// 点击打开文件对话框确定按钮，将文件保存到数据库中
/// </summary>
/// <param name=”sender”></param>
/// <param name=”e”></param>
private void openFileDialog1_FileOk(object sender, System.ComponentModel.CancelEventArgs e)
{
string filename = this.openFileDialog1.FileName;
SqlConnection conn = new SqlConnection(“server=192.168.2.200;integrated security = sspi;database = northwind”);
SqlCommand cmd = new SqlCommand(“insert imgtable values(@imgname,@imgData)”,conn);
SqlParameter pm = new SqlParameter(“@imgname”,SqlDbType.VarChar,100);
pm.Value = filename;
SqlParameter pm1 = new SqlParameter(“@imgData”,SqlDbType.Image);
FileStream fs = new FileStream(filename,FileMode.Open);
int len = (int)fs.Length;
byte[] fileData = new byte[len];
fs.Read(fileData,0,len);
fs.Close();

pm1.Value = fileData;
cmd.Parameters.Add(pm);
cmd.Parameters.Add(pm1);

conn.Open();
try
{
cmd.ExecuteNonQuery();
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}

}

private void button1_Click(object sender, System.EventArgs e)
{
this.openFileDialog1.ShowDialog();
}

/// <summary>
/// 从数据库中读取bitmap图片并显示
/// </summary>
/// <param name=”sender”></param>
/// <param name=”e”></param>
private void button2_Click(object sender, System.EventArgs e)
{
SqlConnection conn = new SqlConnection(“server=192.168.2.200;integrated security = sspi;database = northwind”);
SqlCommand cmd = new SqlCommand(“select * from imgtable where imgname like ‘%bmp%’”,conn);
conn.Open();
SqlDataReader dr;
try
{
dr = cmd.ExecuteReader();
dr.Read();
System.Data.SqlTypes.SqlBinary sb = dr.GetSqlBinary(2);
//或byte[] imageData = (byte[])dr[2];
MemoryStream ms = new MemoryStream(sb.Value);//在内存中操作图片数据
Bitmap bmp = new Bitmap(Bitmap.FromStream(ms));
this.pictureBox1.Image = bmp;
dr.Close();
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
conn.Close();
}
}

/// <summary>
/// 读取文件并保存到硬盘，然后打开文件
/// </summary>
/// <param name=”sender”></param>
/// <param name=”e”></param>
private void button3_Click(object sender, System.EventArgs e)
{
SqlConnection conn = new SqlConnection(“server=192.168.2.200;integrated security = sspi;database = northwind”);
SqlCommand cmd = new SqlCommand(“select * from imgtable where imgname like ‘%doc’”,conn);
conn.Open();
SqlDataReader dr;
try
{
dr = cmd.ExecuteReader();
dr.Read();
System.Data.SqlTypes.SqlBinary sb = dr.GetSqlBinary(2);
//或byte[] imageData = (byte[])dr[2];
//FileStream fs = new FileStream(@”C:\\temp.bmp”,FileMode.Create);
string filename = @”C:\\” + System.IO.Path.GetFileName(dr.GetString(1));
FileStream fs = new FileStream(filename,FileMode.Create);
fs.Write(sb.Value,0,sb.Value.Length);
fs.Close();
//this.pictureBox1.Image = Image.FromFile(@”C:\\temp.bmp”);
System.Diagnostics.Process.Start(filename);
dr.Close();
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
conn.Close();
}
}
}
}

直接把整个文件读取到内存中的数组里对于小文件来说是没问题的，但如果是大文件，特别是大小都超过了物理内存的文件，可能会导致严重的内存问题，需要分段读取，并分段写到数据库。

来源:网络