读写数据库图象字段

从论坛上看到好多人在讨论这方面的问题，把代码整理出来，说不定回答问题的时候还能用上呢。

首先，是数据库的设计。我使用的Access数据库。定义一个数据表photo.mdb，定义两个字段photoID和photo ,其中photoID为主键，字段类型为“文本”，photoID的字段类型为“OLE对象”。（注意：如果采用SQL数据库photo的字段类型为“image “。

以字节形式读写数据库图象字段：

 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
using System.IO;

namespace WindowsApplication2
...{
    public partial class Form1 : Form
    ...{
        public OleDbConnection dbconn = new OleDbConnection();
        public OleDbCommand comm = new OleDbCommand();
        public Form1()
        ...{
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        ...{
            this.OpenConn();
            this.pictureBox1.Image = null;
            Image im;
            this.getPhoto("0000", out im);
            this.pictureBox1.Image = im;
           
        }
        /**//// <summary>
        /// 从数据库中读取图象
        /// </summary>
        /// <param name="pid"></param>
        /// <param name="im"></param>
        public void getPhoto(string pid, out Image im)
        ...{
            //读取图象 
            im = null;
            OleDbDataReader dr = SelectDR("select top 1 photo from photo where photoid='" + pid + "'");
            if (dr.HasRows)
            ...{
                dr.Read();
                if (dr[0] != DBNull.Value)
                ...{
                    try
                    ...{
                        Byte[] byteBLOBData = new Byte[0];

                        byteBLOBData = (Byte[])dr[0];
                        MemoryStream stmBLOBData = new MemoryStream(byteBLOBData);
                        im = Image.FromStream(stmBLOBData);
                    }
                    catch (Exception ex)
                    ...{
                        MessageBox.Show(ex.Message);
                    }
                }
                else
                ...{
                    im = null;
                }
            }
            dr.Close();

        }
        /**//// <summary>
        /// 查询
        /// </summary>
        /// <param name="SqlStr"></param>
        /// <returns></returns>
        public OleDbDataReader SelectDR(string SqlStr)
        ...{
            OleDbCommand cmd = new OleDbCommand(SqlStr, dbconn );
            return cmd.ExecuteReader();
        }
        /**//// <summary>
        /// 打开数据库连接。
        /// </summary>
        public void OpenConn()
        ...{
            if (dbconn.State.ToString() == "Closed")
            ...{
                //DBConn.ConnectionString=ConfigurationSettings.AppSettings["constring"];    //."user id=sa;data source=127.0.0.1;persist security info=True;initial catalog=PPF;password=7388";
                dbconn.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0 ;Data Source=" + Application.StartupPath + @"dataphoto.mdb;User ID=Admin;Password=";
                try
                ...{
                    dbconn.Open();
                }
                catch
                ...{
                    MessageBox.Show("数据库连接失败");
                }

            }
        }
        private void button1_Click(object sender, EventArgs e)
        ...{
            savePhoto("0000", this.pictureBox1.Image);
        }
        /**//// <summary>
        /// 保存图象到数据库
        /// </summary>
        /// <param name="pid"></param>
        /// <param name="im"></param>
        public void savePhoto(string pid, Image im)
        ...{
            OleDbCommand cmd;
            OleDbDataReader dr = SelectDR("select photoid from  photo where photoID='" + pid + "'");

            if (dr.HasRows) //is exist
            ...{
                cmd = new OleDbCommand("Update photo set photoID=@pid, photo=@photo where photoID='" + pid + "'", dbconn );
            }
            else  // not exist
            ...{
                cmd = new OleDbCommand("Insert Into photo (photoID,photo) Values(@pid,@photo) ", dbconn );
            }
            dr.Close();
            cmd.Parameters.Clear();
            cmd.Parameters.AddWithValue ("@pid", pid);
            cmd.Parameters.AddWithValue ("@photo", DBNull.Value);

            //将图片保存到数据库中 
            if (im == null)
            ...{
                cmd.Parameters["@photo"].Value = DBNull.Value;
            }
            else
            ...{
                try
                ...{
                    MemoryStream ms = new MemoryStream();
                    im.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                    byte[] myData = new Byte[ms.Length];
                    ms.Position = 0;
                    ms.Read(myData, 0, Convert.ToInt32(ms.Length));
                    cmd.Parameters["@photo"].Value = myData;

                }
                catch (System.Exception ee)
                ...{
                    MessageBox.Show(ee.Message);
                }
            }//else 

            cmd.ExecuteNonQuery();
        }
    }
}