如何在SQL Server c#中向image列插入null值

2019年7月28日 368次阅读

我一直试图弄清楚如何使用null和image值将图像保存到数据库中.对于我的代码,它保存图像,但如果图像丢失,则不保存空值.

public string STDNAME { get; set; }
public string Image { get; set; }
DateTime Date1 = DateTime.Now;

这是我用来保存数据的代码

public string imagepath { get; set; }

public bool Insert(StudentC c)
{
    bool isSuccess = false;

    SqlConnection conn = new SqlConnection(myconnstring);

    try
    {
        byte[] imageBT = null;

        FileStream fstream = new FileStream(this.Image, FileMode.Open, FileAccess.Read);
        BinaryReader br = new BinaryReader(fstream);
        imageBT = br.ReadBytes((int)fstream.Length);
        string sql = "INSERT INTO STUDENT (STDNAME,imagepath,Image,Date) VALUES (@STDNAME,@imagepath,@Image,@Date)";

        SqlCommand cmd = new SqlCommand(sql, conn);

        cmd.Parameters.AddWithValue("@STDNAME", c.STDNAME);
        cmd.Parameters.AddWithValue("@imagepath", c.imagepath);
        cmd.Parameters.AddWithValue("@Image", imageBT);
        cmd.Parameters.AddWithValue("@Date", Date1);

        conn.Open();

        int rows = cmd.ExecuteNonQuery();

        if (rows > 0)
        {
            isSuccess = true;
        }
        else
        {
            isSuccess = false;
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine("\nMessage ---\n{0}", ex.Message);
    }
    finally
    {
        conn.Close();
    }

    return isSuccess;
}

此代码用于浏览图像

//browse image
private void button6_Click(object sender, EventArgs e)
{
    OpenFileDialog f = new OpenFileDialog();
    f.Filter = "All Files|*.*|JPEGs|*.jpg|Bitmaps|*.bmp|GIFs|*.gif";
    f.FilterIndex = 2;

    if (f.ShowDialog() == DialogResult.OK)
    {
        pictureBox2.Image = Image.FromFile(f.FileName);
        pictureBox2.SizeMode = PictureBoxSizeMode.StretchImage;
        pictureBox2.BorderStyle = BorderStyle.Fixed3D;
        textBox7.Text = f.SafeFileName.ToString();
        string picPath = f.FileName.ToString();
        textBox7.Text = picPath;
        pictureBox2.ImageLocation = picPath;
    }
}

这是为存储提供值的代码

private void button5_Click(object sender, EventArgs e)
{
    c.STDNAME = textBox2.Text;

    c.Image = textBox7.Text;
    c.imagepath = textBox7.Text;

    bool success = c.Insert(c);

    if (success == true)
    {
        MessageBox.Show("Data has been saved");
        //Clear();
    }
    else
    {
        //    label4.Text = "Data Has not been saved";
        MessageBox.Show("Data has not been saved");
    }
}

最佳答案 要向图像列添加null,请确保指定类型(例如VarBinary),如下例所示.此外,请确保image列接受null.

cmd.Parameters.Add("@Image", SqlDbType.VarBinary).Value = DBNull.Value;

此外,以下方法可能会导致以下例外情况：

cmd.Parameters.AddWithValue("@Image", DBNull.Value);

—例外—

System.Data.SqlClient.SqlException (0x80131904): Implicit conversion from data type nvarchar to varbinary(max) is not allowed. Use the CONVERT function to run this query.
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