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();

   //
   // TODO: 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。