如何检查我是否有来自 SQL 服务器数据库的图像或不使用 C#

Question

I have a Winforms application which stores products from clients. Those products can have an image to describe them.

My problem is that when I want to change my product information I'm getting the following exception:

System.InvalidCastException: 'Impossible to cast an object of type "System.DBNull" in type "System.Byte[]"

I know this exception occurs because I don't have an image in my database, but I want to know how to check if the image exists.

My code:

private void chargeImage()
{
    SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["db"].ConnectionString);

    SqlCommand com1 = new SqlCommand("SELECT * FROM [dbo].[Product] WHERE RFID = '" + dataview.SelectedRows[0].Cells[0].Value.ToString() + "'", con);   // Charge image

    con.Open();

    SqlDataReader dr = com1.ExecuteReader();

    if (dr.Read())
    { 
        byte[] picArr = (byte[])dr["image"];
        ms = new MemoryStream(picArr);
        ms.Seek(0, SeekOrigin.Begin);
        pictureBox1.Image = Image.FromStream(ms);
    }

    con.Close();
}

Answer 1

You can check is it is not DBNull. Before

byte[] picArr = (byte[])dr["image"];

you can check

if (!Convert.IsDBNull(dr["image"]))

Answer 2

you can check if they contain null value:

byte[] picArr = dr.IsDBNull("image")? null: (byte[])dr["image"];