c# - Getting return value from stored procedure in ADO.NET

Question

I have a stored procedure, which returns the unique identifier after insertion @@identity. I tried it in the server explorer and it works as expected @RETURN_VALUE = [identifier].

In my code I added a parameter called @RETURN_VALUE, with ReturnValue direction first, than any other parameters, but when I run my query with ExecuteNonQuery() that parameter remains empty. I don't know what I've done wrong.

Stored Procedure

 ALTER PROCEDURE dbo.SetAuction
 (
  @auctionID int,
  @itemID int,
  @auctionType tinyint,
  @reservationPrice int,
  @maxPrice int,
  @auctionEnd datetime,
  @auctionStart datetime,
  @auctionTTL tinyint,
  @itemName nchar(50),
  @itemDescription nvarchar(MAX),
  @categoryID tinyint,
  @categoryName nchar(50)
 ) AS
 IF @auctionID <> 0
  BEGIN
   BEGIN TRAN T1
   
   UPDATE Auction
   SET  AuctionType   = @auctionType,
     ReservationPrice = @reservationPrice,
     MaxPrice    = @maxPrice,
     AuctionEnd    = @auctionEnd,
     AuctionStart   = @auctionStart,
     AuctionTTL    = @auctionTTL
   WHERE AuctionID    = @auctionID;
   
   UPDATE Item
   SET
    ItemName  = @itemName,
    ItemDescription = @itemDescription
   WHERE
    ItemID = (SELECT ItemID FROM Auction WHERE AuctionID = @auctionID);
   
   COMMIT TRAN T1
   
   RETURN @auctionID
  END
 ELSE
  BEGIN
   BEGIN TRAN T1
    INSERT INTO Item(ItemName, ItemDescription, CategoryID)
    VALUES(@itemName, @itemDescription, @categoryID);
    
    INSERT INTO Auction(ItemID, AuctionType, ReservationPrice, MaxPrice, AuctionEnd, AuctionStart, AuctionTTL)
    VALUES(@@IDENTITY,@auctionType,@reservationPrice,@maxPrice,@auctionEnd,@auctionStart,@auctionTTL);
   COMMIT TRAN T1
   RETURN @@IDENTITY
  END

C# Code

cmd.CommandText = cmdText;
SqlParameter retval = new SqlParameter("@RETURN_VALUE", System.Data.SqlDbType.Int);
retval.Direction = System.Data.ParameterDirection.ReturnValue;
cmd.Parameters.Add(retval);
cmd.Parameters.AddRange(parameters);
cmd.Connection = connection;

connection.Open();
cmd.ExecuteNonQuery();

return (int)cmd.Parameters["@RETURN_VALUE"].Value;

Answer 1

Just tried on my box and this works for me:

In SQL Server:

DROP PROCEDURE TestProc;
GO
CREATE PROCEDURE TestProc
AS
   RETURN 123;
GO

In C#

        string cnStr = "Server=.;Database=Sandbox;Integrated Security=sspi;";
        using (SqlConnection cn = new SqlConnection(cnStr)) {
            cn.Open();
            using (SqlCommand cmd = new SqlCommand("TestProc", cn)) {
                cmd.CommandType = CommandType.StoredProcedure;
                SqlParameter returnValue = new SqlParameter();
                returnValue.Direction = ParameterDirection.ReturnValue;
                cmd.Parameters.Add(returnValue);

                cmd.ExecuteNonQuery();
                Assert.AreEqual(123, (int)returnValue.Value);
            }
        }