[英]ASP.NET CORE stored procedure error : InvalidCastException
[英]Stored procedure InvalidCastException error
我試圖在一個簡單的控制台應用程序中訪問存儲過程,由於某種原因,我收到了InvalidCastException
。
有人可以幫忙嗎?
class Customer
{
public int CustomerID { get; set; }
public string FirstName { get; set; }
public string SecondName { get; set; }
public int Age { get; set; }
}
static void Main(string[] args)
{
string storedProc = "dogssimple";
List<Customer> custList = new List<Customer>();
SqlConnection conn = new SqlConnection("server=localhost;" +
"Trusted_Connection=yes;" +
"database=mydatabase; " +
"connection timeout=30");
try
{
conn.Open();
SqlCommand cmd = new SqlCommand(storedProc, conn);
cmd.CommandType = CommandType.StoredProcedure;
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Customer addCustomer = new Customer() //..... cast exception here
{
CustomerID = (int)rdr["CustomerID"],
FirstName = (string)rdr["FirstName"],
SecondName = (string)rdr["SecondName"],
Age = (int)rdr["Age"],
}; //....
Console.WriteLine("Customer: {0}, {1}, {2}, {3}", addCustomer.CustomerID, addCustomer.FirstName, addCustomer.Age, addCustomer.Age);
custList.Add(addCustomer);
}
var age = from x in custList
select x.Age;
var avgAge = age.Average();
Console.WriteLine("The average age of the customers is " + avgAge);
}
catch (Exception e)
{
Console.WriteLine(e); ;
}
Console.ReadLine();
}
ADO.NET返回空值作為DBNull實例(如果您問我,這很奇怪)。 因此,請通過以下檢查來讀取值:
SecondName = rdr["SecondName"] is DBNull ? null : (string)rdr["SecondName"]
還要確保數字類型匹配,例如。 您可能需要一個整數,但可能會得到一個浮點數或一個十進制數。
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