asp.net – 错误：必须声明标量变量“@data”

当执行到达cmd.ExecuteNonQuery()时,我收到一个错误,其中说必须声明标量变量：

OleDbCommand cmd = new OleDbCommand();
cmd.Connection = Connection;
cmd.CommandTimeout = 0;

string commandText = "update groups set subjectline ='" +    txtSubjectLine.Text + "',data= @data where groupid = " + ddlGroup.SelectedItem.Value + " ";
cmd.CommandText = commandText;
cmd.CommandType = CommandType.Text;

cmd.Parameters.Add("@Data",OleDbType.VarBinary);
cmd.Parameters["@Data"].Value = binarydata;               
cmd.ExecuteNonQuery();

解决方法

更换

string commandText = "update groups set subjectline ='" +    txtSubjectLine.Text + "',data= @data where groupid = " + ddlGroup.SelectedItem.Value + " ";

同

string commandText = "update groups set subjectline ='" +    txtSubjectLine.Text + "',data= ? where groupid = " + ddlGroup.SelectedItem.Value + " ";

也就是说,将“@data”替换为“？”在命令文本中.这是使用OleDbCommand指定参数占位符的方法.

这是编辑过的原文：

OleDbCommand cmd = new OleDbCommand();
cmd.Connection = Connection;
cmd.CommandTimeout = 0;

cmd.CommandText = "update groups set subjectline ='" + txtSubjectLine.Text + "',data = ? where groupid = " + ddlGroupSelectedItem.Value;
cmd.CommandType = CommandType.Text;

cmd.Parameters.Add("p1",OleDbType.VarBinary);
cmd.Parameters["p1"].Value = binarydata;

cmd.ExecuteNonQuery();