C# “什么是”呢;参数化查询。。。没有提供的;错误?
我在上遇到了一个错误C# “什么是”呢;参数化查询。。。没有提供的;错误?,c#,httphandler,C#,Httphandler,我在上遇到了一个错误 "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) {
"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();
使用替代方法
您应该在命令中为参数提供@
Soner Gönül,图像为空。我怎样才能纠正它
因此,如果image
为null
,则应返回DBNull.Value
。不能对所需参数传递null
。您可以使用一种方法作为替代方法,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;
}
嗨,谢谢你!然而,它不起作用。同样的错误仍然发生。@LiuJiaHui检查我更新的问题。记住使用
@blue
而不是blue
@LiuJiaHui您确定您的图像
不为空吗?请与调试器联系。@LiuJiaHui更新了我的问题。让我们
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;
}