在MVC4中下载文件方法

Question

当我尝试下面的代码时，我收到了“运算符不存在：整数= @整数”和ArgumentException。

有人可以帮我解决这个问题吗？

public FileContentResult GetFile(int fileid)
{
     NpgsqlDataReader rdr;
     byte[] fileContent = null;
     string mimeType=" ";
     string fileName=" "; 
    NpgsqlConnection conn = new       NpgsqlConnection(ConfigurationManager.ConnectionStrings["portalconnectionstring"].ConnectionString);
using (portalconnectionstring ps = new portalconnectionstring())
{
    var query = "select filename,content_type,filedata from tblfiles where     fileid='"+fileid+"'";
  var cmd = new NpgsqlCommand(query, conn);
  cmd.Parameters.AddWithValue("@fileid", fileid);
  conn.Open();
  rdr = cmd.ExecuteReader();
  if (rdr.HasRows)
  {
     rdr.Read();
     fileContent=(byte[]) rdr["filedata"];
     mimeType = rdr["content_type"].ToString();
    fileName = rdr["filename"].ToString()
  }
 }
conn.Close();
return File(fileContent, mimeType, fileName);
}