如何使用Visual C＃从SQL Server表中获取ID号

作为初学者，我一直在培训数据库和C＃编程概念。 我刚刚在SQL Server中创建了一个表，并在其中插入了一些图像文件。

我还创建了一个表单项目，将图像保存到该数据库表并检索以在图片框中显示它们。

我正在尝试获取ID号并加载到combobox，以便我可以选择相关图像的ID号。 我设法将图像文件保存到DB但我无法将ID号检索到combobox中。

我恳请您提供简单的解释和一些建议。 你可以在下面查看我的代码。

public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void button1_Click(object sender, EventArgs e) { SqlConnection con = new SqlConnection(DBHandler.GetConnectionString()); try { OpenFileDialog fop = new OpenFileDialog(); fop.InitialDirectory = @"C:\"; fop.Filter = "[JPG,JPEG]|*.jpg"; if (fop.ShowDialog() == DialogResult.OK) { FileStream FS = new FileStream(@fop.FileName, FileMode.Open, FileAccess.Read); byte[] img = new byte[FS.Length]; FS.Read(img, 0, Convert.ToInt32(FS.Length)); if (con.State == ConnectionState.Closed) con.Open(); SqlCommand cmd = new SqlCommand("SaveImage", con); cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.Add("@img", SqlDbType.Image).Value = img; cmd.ExecuteNonQuery(); //loadImageIDs(); MessageBox.Show("Image Save Successfully!!", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information); } else { MessageBox.Show("Please Select a Image to save!!", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information); } } catch (Exception ex) { MessageBox.Show(ex.Message, "Exception", MessageBoxButtons.OK, MessageBoxIcon.Error); } finally { if (con.State == ConnectionState.Open) con.Close(); } } private void button3_Click(object sender, EventArgs e) { SqlConnection con2 = new SqlConnection(DBHandler.GetConnectionString()); SqlCommand cmd2 = new SqlCommand("ReadImage",con2); cmd2.CommandType = CommandType.StoredProcedure; cmd2.Parameters.Add("@imgId", SqlDbType.Int).Value = Convert.ToInt32(comboBox1.SelectedValue.ToString()); // I am not sure if this line is correct to get images from the table using "ReadImage" procedure. SqlDataAdapter da = new SqlDataAdapter(); da.SelectCommand = cmd2; DataTable dt = new DataTable(); da.Fill(dt); dataGridView1.DataSource = dt; } private void button2_Click(object sender, EventArgs e) // I have a problem within this code block, I think :) { SqlConnection con3 = new SqlConnection(DBHandler.GetConnectionString()); SqlCommand cmd3 = new SqlCommand("ReadAllImageIDs", con3); cmd3.CommandType = CommandType.StoredProcedure; SqlDataAdapter dc = new SqlDataAdapter(); dc.SelectCommand = cmd3; DataTable dtt = new DataTable(); dc.Fill(dtt); comboBox1.DataSource = dtt; //dataGridView1.DataSource = dtt; } 

Answer 1

我认为你需要为你的ComboBox设置你的DisplayMember和ValueMember 。 例如

  comboBox1.DisplayMember = "ID"; 

当使用实现IDisposable （SqlConnection，SqlCommand，SqlDataAdapter）的对象using块来确保它们被正确处理时，这也是一个好主意。 所以你的方法可能变成：

 private void button2_Click(object sender, EventArgs e) { var dtt = new DataTable(); using (var con3 = new SqlConnection(DBHandler.GetConnectionString())) using (var cmd3 = new SqlCommand("ReadAllImageIDs", con3)) { cmd3.CommandType = CommandType.StoredProcedure; using(var dc = new SqlDataAdapter()) { dc.SelectCommand = cmd3; dc.Fill(dtt); comboBox1.DataSource = dtt; comboBox1.DisplayMember = "ID"; comboBox1.ValueMember = "ID"; } } } 

您还可以使用带有select命令的SqlDataAdapter构造函数和连接字符串作为参数来快速执行此操作，因此您可以简化为：

 private void button2_Click(object sender, EventArgs e) { var dtt = new DataTable(); using (var dc = new SqlDataAdapter("ReadAllImageIDs", DBHandler.GetConnectionString())) { dc.SelectCommand.CommandType = CommandType.StoredProcedure; dc.Fill(dtt); } comboBox1.DataSource = dtt; comboBox1.DisplayMember = "ID"; comboBox1.ValueMember = "ID"; } 

另外请注意，将数据访问层（DAL）与UI分离通常是个好主意。 所以你可能有一个单独的类，可能在一个单独的库中：

 public class ImageService { public static void SaveImage(string fileName) { byte[] img; using(var fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read)) { img = new byte[fileStream.Length]; fileStream.Read(img, 0, Convert.ToInt32(fileStream.Length)); } using (var con = new SqlConnection(DBHandler.GetConnectionString())) using (var cmd = new SqlCommand("SaveImage", con)) { con.Open(); cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.Add("@img", SqlDbType.Image).Value = img; cmd.ExecuteNonQuery(); } } public static DataTable GetAllImageIDs { var dtt = new DataTable(); using (var dc = new SqlDataAdapter("ReadAllImageIDs", DBHandler.GetConnectionString())) { dc.SelectCommand.CommandType = CommandType.StoredProcedure; dc.Fill(dtt); } return dtt; } } 

然后在您的UI中，您只需：

 private void button1_Click(object sender, EventArgs e) { try { OpenFileDialog fop = new OpenFileDialog(); fop.InitialDirectory = "C:\\"; fop.Filter = "[JPG,JPEG]|*.jpg"; if (fop.ShowDialog() == DialogResult.OK) { ImageService.SaveImage(fop.FileName); } } catch (Exception ex) { MessageBox.Show(ex.Message, "Exception", MessageBoxButtons.OK, MessageBoxIcon.Error); } } private void button2_Click(object sender, EventArgs e) { comboBox1.DataSource = ImageService.GetAllImageIDs(); comboBox1.DisplayMember = "ID"; comboBox1.ValueMember = "ID"; } 

Answer 2

如果你正在努力使用combobox或SQL，那就不太清楚了。

这应该给你一个良好的开端：

  List ids = new List(); using (SqlConnection conn = new SqlConnection("MyConnectionString")) { using (SqlCommand cmd = new SqlCommand("MyStoredProcedure", conn)) { conn.Open(); using (SqlDataReader rdr = cmd.ExecuteReader()) { while (rdr.Read()) { ids.Add(rdr["NameOfIsField"].ToString()); } } } } MyListBox.DataSource = ids; 

考虑：

• 您的存储过程正在返回
• 是否向用户显示ID是有意义的