When using a Stored procedure on SQL 2008 and C# 4.0, I am unable to retrieve OUTPUT information and return info from a Select statement. I keep getting "Object reference not set to an instance of an object.". When i do ExecuteScalar() i get the rows, but not the data. Found a few examples out there and they look like what i'm doing, so i think i'm missing something simple in front of me. Thanks.
Stored procedure
USE [PhoneDb]
GO
/****** Object: StoredProcedure [dbo].[TestPagingProcedure] Script Date: 06/16/2011 08:39:03 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[TestPagingProcedure]
-- Add the parameters for the stored procedure here
@startRowIndex int,
@maximumRows int,
@totalRows int OUTPUT
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
DECLARE @first_id UNIQUEIDENTIFIER
DECLARE @startRow int
SET @startRowIndex = (@startRowIndex - 1) * @maximumRows
IF @startRowIndex = 0
SET @startRowIndex = 1
SET ROWCOUNT @startRowIndex
SELECT @first_id = ExtensionGUID FROM ExtItem ORDER BY ExtensionGUID
PRINT @first_id
SET ROWCOUNT @maximumRows
SELECT
ExtensionGUID, AesExt, AesHashPassword, ToNumber, AgentExt, Name, JpgImageName, BigImageName, WbmpImageName
FROM ExtItem WHERE
ExtensionGUID >= @first_id
ORDER BY ExtensionGUID
SET ROWCOUNT 0
-- GEt the total rows
SELECT @totalRows = COUNT(ExtensionGUID) FROM ExtItem
END
C# Code
public bool GetPagedResults(string startRowIndex, string maxRows, ref double totalRowsReturned)
{
bool IsSuccess = false;
string clearPassword = "";
Log.WriteLine("GetExtList : ENTERED GETEXTITEM: ", Log.DEBUG_LEVEL.VERBOSE);
SqlConnection MyConnection = null;
EnDecrypt hasher = null;
try
{
if (SQLLookup.DatabaseString == "")
{
Log.WriteLine("GetPagedResults : SQLLookup.DatabaseString is empty:", Log.DEBUG_LEVEL.VERBOSE);
SQLLookup.SQLFinder();
Log.WriteLine("GetPagedResults : SQL FINDER RUN: SQLLookup.DatabaseString:'" + SQLLookup.DatabaseString + "'", Log.DEBUG_LEVEL.VERBOSE);
}
Log.WriteLine("GetPagedResults: SQL Server '" + SQLLookup.DatabaseString + "'", Log.DEBUG_LEVEL.VERBOSE);
_extItemList.Clear(); // Keep new records from just being appended to existing list.
hasher = new EnDecrypt("SetMyKey", "SaltGenerator");
// Create a Connection to SQL Server
MyConnection = new SqlConnection(@"Data Source= " + SQLLookup.DatabaseString + @"; Initial Catalog=PhoneDb;Integrated Security=True");
SqlCommand myCommand = new SqlCommand("TestPagingProcedure", MyConnection);
myCommand.CommandType = CommandType.StoredProcedure;
/* ASSIGN PARAMETERS */
myCommand.Parameters.Add(new SqlParameter("@startRowIndex", startRowIndex));
myCommand.Parameters.Add(new SqlParameter("@maximumRows", maxRows));
myCommand.Parameters.Add("@totalRows", SqlDbType.Int, 4);
myCommand.Parameters["@totalRows"].Direction = ParameterDirection.Output;
Log.WriteLine("GetPagedResults:3 After try ", Log.DEBUG_LEVEL.VERBOSE);
Log.WriteLine("GetPagedResults:3 startRowIndex = " + startRowIndex + " maxRows = " + maxRows, Log.DEBUG_LEVEL.VERBOSE);
MyConnection.Open();
SqlDataReader Reader = myCommand.ExecuteReader();
Log.WriteLine("GetPagedResults BEFORE WHILE LOOP", Log.DEBUG_LEVEL.VERBOSE);
while (Reader.Read())
{
/* BUILD EXT ITEM*/
ExtItem extItem = new ExtItem();
if (Reader.IsDBNull(0) || Reader.GetGuid(0) == Guid.Empty)
extItem.ExtensionGUID = Guid.Empty;
else
extItem.ExtensionGUID = Reader.GetGuid(0);
if (Reader.IsDBNull(1) || Reader.GetString(1) == "")
extItem.AesExt = "No value";
else
extItem.AesExt = Reader.GetString(1);
/* ADD ITEM TO LIST */
AddItem(extItem);
//Log.WriteLine("GetExtList extItem: " + extItem.ToString(), Log.DEBUG_LEVEL.VERBOSE);
}
// get the total rows
Log.WriteLine("GetPagedResults: New Total number of pages: " + (int)myCommand.Parameters[2].Value, Log.DEBUG_LEVEL.TERSE);
// totalRowsReturned = myCommand.Parameters["@totalRows"];
IsSuccess = true;
MyConnection.Close();
Log.WriteLine("GetPagedResults: RETURNING:", Log.DEBUG_LEVEL.VERBOSE);
}
catch (Exception ex)
{
Log.WriteLine("GetPagedResults: Unable to retrieve Extension list. Caught Exception " + ex.Message,
Log.DEBUG_LEVEL.TERSE);
IsSuccess = false;
}
MyConnection.Close();
return IsSuccess;
}
To retrieve data using a DataReader, create an instance of the Command object, and then create a DataReader by calling Command. ExecuteReader to retrieve rows from a data source.
1) Duplicate the stored procedure and add the FOR XML to the return statement(not pretty but works). 2) Have a second stored procedure call the non-XML version and just return the results using FOR XML . 3) Build the XML in the SELECT statement of the stored procedure.
ExecuteReader() Sends the CommandText to the Connection and builds a SqlDataReader. ExecuteReader(CommandBehavior) Sends the CommandText to the Connection, and builds a SqlDataReader using one of the CommandBehavior values.
According to, http://msdn.microsoft.com/en-us/library/ms971497, you must close the datareader before you process the output parameters.
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