[英]What is “The parameterized query … which was not supplied.” error?
我在遇到错误
"The parametrized query '(@blue nvarchar(4000))SELECT blueBallImage FROM CorrespondingBal' expects the parameter '@blue',
which was not supplied."
我正在做一个HttpHandler。
我想从数据库中检索图像。 我的代码如下。
public void ProcessRequest (HttpContext context) {
string image = context.Request.QueryString["image"];
SqlConnection con = new SqlConnection(@"Data Source=localhost;Initial Catalog=MyCloudGames;Integrated Security=True");
SqlCommand cmd = new SqlCommand("SELECT blueBallImage FROM CorrespondingBall WHERE objective = blue", con);
cmd.CommandType = CommandType.Text;
cmd.Parameters.Add("blue", image);
con.Open();
byte[] ballImage = (byte[])cmd.ExecuteScalar();
con.Close();
context.Response.ContentType = "image/png";
context.Response.OutputStream.Write(ballImage, 78, ballImage.Length - 78);
}
错误发生在
byte[] ballImage = (byte[])cmd.ExecuteScalar();
使用AddWithValue
而不是Add
方法。
SqlCommand cmd = new SqlCommand("SELECT blueBallImage FROM CorrespondingBall WHERE objective = @blue", con);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@blue", image);
您应该在命令中使用@
来提供参数。
SonerGönül,图片为空。 我该如何纠正?
因此,如果image
为null
,则应返回DBNull.Value
。 您不能在必填参数上传递null
。 您可以将方法用作替代方法;例如:
SqlCommand cmd = new SqlCommand("SELECT blueBallImage FROM CorrespondingBall WHERE objective = @blue", con);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@blue", CheckForDbNull(image));
...
public static object CheckForDbNull(object value)
{
if(value == null)
{
return DBNull.Value;
}
return value;
}
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