c# - Conditions fails when 2 user are doing the delete action -


my problem pretty straightforward, have page admins can manage list of authorized admin problem there should @ least 1 admin left in database wrote simple if checks number of admins in database should higher 1 before deleting

here controller delete action

 public actionresult deleteadmin(int idadmin)     {          using (inscriptionformationentities dbm = new inscriptionformationentities())         {             administrateurs admin = dbm.administrateurs.firstordefault(x => x.id == idadmin);             if(admin.nomlogin == session["utilisateur"].tostring())             {                 modelstate.addmodelerror("current user", "you can't delete yourself");             }             if(dbm.administrateurs.tolist().count <= 1)             {                 modelstate.addmodelerror("lastadmin", "at least 1 admin must left");             }             if (modelstate.isvalid)             {                 dbm.administrateurs.remove(admin);                 dbm.savechanges();             }             list<administrateurs> listeadmin = dbm.administrateurs.tolist();             return redirecttoaction("utilisateurs", "admin");         }     }

this code works fine expect in 1 case : if there 2 admin left , try delete eachother @ same time able to. tried change put condition(for instance before delete) still condition returns false. wondering if there way prevent defining 1 instance can delete @ time or that.

edit

i looked question: how can lock table on read, using entity framework?

but dosen't solve problem because don't want lock on read on delete instead, because if lock read 1 person able access page @ time ( work in worse case scenario hope there better solution)

if willing use stored procedures use sp_getapplock. works mutex in stored procedure. in protected code section record count , delete knowing call procedure not execute code until lock released.

i have added example procedure, ignore set @msg , raiserror statements these there display status, important bit starts @ exec statement.

run procedures in 2 separate tabs, both start second wait 15 seconds acquire lock , continue if gets it.

exec critical_rhz '00:00:20' simulates process take 20 seconds 

create proc dbo.critical_rhz  @wait_duration varchar(30) = '00:01:00' -- default 1 minute /* performs task in critical section of code can run    1 session or transaction @ time.     task simulated wait     raiseerror() nowait real time status displays */ declare @rc int = 0 -- return code   , @msg varchar(2000) set @msg = convert(varchar,getdate(), 114) + ' critical_section_worker starting' raiserror (@msg, 0, 1) nowait  begin try begin tran set @msg= convert(varchar,getdate(), 114) + ' requesting lock' raiserror (@msg, 0, 1) nowait exec @rc = sp_getapplock @resource='criticalsectionworker' -- resource locked      , @lockmode='exclusive'  -- type of lock      , @lockowner='transaction' -- transaction or session      , @locktimeout = 15000 -- timeout in milliseconds, 15 seconds set @msg= convert(varchar,getdate(), 114) + ' sp_getapplock returned ' + convert(varchar(30), @rc) + ' -- '   + case when @rc < 0 'could not obtain lock'  else 'lock obtained'  end raiserror (@msg, 0, 1) nowait  if @rc >= 0 begin   set @msg= convert(varchar,getdate(), 114) + ' got lock starting critical work '   raiserror (@msg, 0, 1) nowait waitfor delay @wait_duration -- critical work simulated waiting   commit tran -- release lock   set @msg= convert(varchar,getdate(), 114) + ' work complete released lock'    raiserror (@msg, 0, 1) nowait   end   else begin   rollback tran   set @rc = 50000 end end try begin catch  set @msg = 'error: ' + error_message() + ' @ '          + coalesce(error_procedure(), '')         + coalesce (' line:' + convert(varchar(30), error_line()), '')  raiserror (@msg, 0, 1) nowait -- ensure message gets out          if @@trancount > 1 rollback tran raiserror (@msg, 16, 1) end catch return @rc go

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