C# SQL Transaction (Process ID 72) was deadlocked

Question

I have created a WinForm in Visual Studio which multiple users will access. Whenever a user access the data I want to lock the data so that the other users cannot view the same data at the same time due to some business logic.

Below is my c# code

using (SqlConnection conn = new SqlConnection(connectString))
{
    using (SqlCommand cmd=new SqlCommand("get_First_Unscan_Record_withUpdate",conn))
    {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@usrName", username_Form);
        conn.Open();
        record_number = cmd.ExecuteScalar().ToString();
    }
}

And My SQL Procedure

    CREATE PROCEDURE [dbo].[get_First_QC_Record_withUpdate]
@usrName nvarchar(50)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

Declare @srno int

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

select top 1 @srno=srno from [KYC].[dbo].[KYC_Index] (XLOCK) where  [qc]='N' and [qc_int]='N' and transform_int='Y' and transform_status='Y' order by srno

update KYC_Index set [qc_int]='Y',[qc_int_by]=@usrName,[qc_int_time]=GETDATE(),@srno=KYC_Index.srno where srno = @srno

select @srno

Still my users are getting deadlock error

{"Transaction (Process ID 72) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction."}

What am I doing wrong? Or should I change? Please guide.

Answer 1

You cannot hide the data by locking it. To hide from other users, there must be column like hidden in the same table or better in externally linked table like hidden_rows . SERIALIZABLE level is also not necessary. You need only BEGIN TRAN / COMMIT TRAN or you can do the same from C# side (begin_tran - try { do_work, commit_tran } catch { rollback }).

https://msdn.microsoft.com/en-us/library/86773566(v=vs.110).aspx

In SELECT statement use (UPDLOCK) hint - it will lock the row for writing until end of transaction and it will be readable for others.