上传一个文件路径到本地数据库(data.sdf)并绑定到gridview，也使用存储文件路径从数据库下载相同的文件

Upload button 
--->> file open dialog box 
 ---->> select file
    --->> Catch the path of the file
      --->> Convert the path of file to bytes
        --->>send to local database (data.sdf)
           --->> bind the filename && path to grid view.

Select the file (single cell) from grid view
  --->>> Download button
     --->> receive the selected file path from local database (data.sdf)
        --->> converts to bytes
           -->> convert to original file
             -->> save dialog box
               --->> save the file on my computer

我找到了解决问题的方法。现在我需要上传一个文件路径到本地数据库(data.sdf)并绑定到gridview，还可以使用存储的文件路径

从数据库下载相同的文件

保存在数据库中的文件代码。

  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.SqlClient;
  using System.IO;
namespace sqlFileExample
{
  public partial class frmMain : Form
{
    SqlConnection objConn = new SqlConnection();
    string strSqlConn = @"Data Source=.'SQLEXPRESS;AttachDbFilename=C:'Users'honesty'Downloads'sqlFileExample'sample db'db2.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
    string strQuery_AllAttachments = "select [id], [fileName], [fileSize] from [tblAttachments] order by [fileName]";
    string strQuery_GetAttachmentById = "select * from [tblAttachments] where [id] = @attachId";
    string strQuery_AllAttachments_AllFields = "select * from [tblAttachments]";
    public frmMain()
    {
        InitializeComponent();
        //prevent resize at runtime
        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle; 
        this.MaximizeBox = false;
        this.MinimizeBox = false;
        this.Text = "SQL file upload/download example";
    }
    private void frmMain_Load(object sender, EventArgs e)
    {
        objConn.ConnectionString = strSqlConn; //set connection params
        FillDataGrid(gridViewMain, strQuery_AllAttachments);
    }
    private void ConnectToDb()
    {
        //objConn.ConnectionString = strSqlConn; //set our connection params
        //objConn.Open(); //open connection
    }
    private void frmMain_FormClosing(object sender, FormClosingEventArgs e)
    {
        //objConn.Close();  //close connection
    }
    private void FillDataGrid(DataGridView objGrid, string strQuery)
    {
        DataTable tbl1 = new DataTable();
        SqlDataAdapter adapter1 = new SqlDataAdapter();
        SqlCommand cmd1 = new SqlCommand();
        cmd1.Connection = objConn;  // use connection object
        cmd1.CommandText = strQuery; // set query to use
        adapter1.MissingSchemaAction = MissingSchemaAction.AddWithKey;  //grab schema
        adapter1.SelectCommand = cmd1; //
        adapter1.Fill(tbl1);  // fill the data table as specified
        objGrid.DataSource = tbl1;  // set the grid to display data
    }
    private void btnAddFile_Click(object sender, EventArgs e)
    {
        if (ofdMain.ShowDialog() != DialogResult.Cancel)
        {
            CreateAttachment(ofdMain.FileName);  //upload the attachment
        }
        FillDataGrid(gridViewMain, strQuery_AllAttachments);  // refresh grid
    }
    private void CreateAttachment(string strFile)
    {
        SqlDataAdapter objAdapter = new SqlDataAdapter(strQuery_AllAttachments_AllFields, objConn);
        objAdapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;
        SqlCommandBuilder objCmdBuilder = new SqlCommandBuilder(objAdapter);
        DataTable objTable = new DataTable();
        FileStream objFileStream = new FileStream(strFile, FileMode.Open, FileAccess.Read);
        int intLength = Convert.ToInt32(objFileStream.Length);
        byte[] objData;
        objData = new byte[intLength];
        DataRow objRow;
        string[] strPath = strFile.Split(Convert.ToChar(@"'"));
        objAdapter.Fill(objTable);
        objFileStream.Read(objData, 0, intLength);
        objFileStream.Close();
        objRow = objTable.NewRow();
        objRow["fileName"] = strPath[strPath.Length - 1]; //clip the full path - we just want last part!
        objRow["fileSize"] = intLength / 1024; // KB instead of bytes
        objRow["attachment"] = objData;  //our file
        objTable.Rows.Add(objRow); //add our new record
        objAdapter.Update(objTable);
    }
    private void btnDownloadFile_Click(object sender, EventArgs e)
    {
        SaveAttachment(sfdMain, gridViewMain);
        FillDataGrid(gridViewMain, strQuery_AllAttachments);  // refresh grid
    }
    private void SaveAttachment(SaveFileDialog objSfd, DataGridView objGrid)
    {
        string strId = objGrid.SelectedRows[0].Cells["id"].Value.ToString();
        string fileName = objGrid.SelectedRows[0].Cells["fileName"].Value.ToString();
        if (!string.IsNullOrEmpty(fileName))
        {
            SqlCommand sqlCmd = new SqlCommand(strQuery_GetAttachmentById, objConn);
            sqlCmd.Parameters.AddWithValue("@attachId", strId);
            SqlDataAdapter objAdapter = new SqlDataAdapter(sqlCmd);
            DataTable objTable = new DataTable();
            DataRow objRow;
            objAdapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;
            SqlCommandBuilder sqlCmdBuilder = new SqlCommandBuilder(objAdapter);
            objAdapter.Fill(objTable);
            objRow = objTable.Rows[0];

            byte[] objData;
            objData = (byte[])objRow["attachment"];
            FileInfo fileInfo = new FileInfo(fileName);
            string fileExtension = fileInfo.Extension;
            //Set Save dialog properties
            objSfd.Filter = "Files (*" + fileExtension + ")|*" + fileExtension;
            objSfd.Title = "Save File as";
            objSfd.CheckPathExists = true;
            objSfd.FileName = fileName;
            if (objSfd.ShowDialog() == DialogResult.OK)
            {
                string strFileToSave = objSfd.FileName;
                FileStream objFileStream = new FileStream(strFileToSave, FileMode.Create, FileAccess.Write);
                objFileStream.Write(objData, 0, objData.Length);
                objFileStream.Close();
            }
        }
    }