/// <summary>
/// Tries to renew the registration session. This method locks tables
/// during processing. After returning, you must check the <see cref="RegistrationSession.RegistrationCount"/>
/// property to ensure that enough spots still exist. This can happen if
/// the session was expired but was able to be partially renewed.
/// </summary>
/// <param name="sessionGuid">The session unique identifier.</param>
/// <returns>The <see cref="RegistrationSession"/> that was renewed or <c>null</c> if it could not be found.</returns>
public static RegistrationSession TryToRenewSession(Guid sessionGuid)
{
using (var rockContext = new RockContext())
{
var registrationSessionService = new RegistrationSessionService(rockContext);
var registrationService = new RegistrationService(rockContext);
RegistrationSession registrationSession = null;
var wasRenewed = rockContext.WrapTransactionIf(() =>
{
/*
* This is an anti-pattern. Do not just copy this and use it
* as a pattern elsewhere. Discuss with the team before trying
* to use this anywhere else.
*
* This single use-case was discussed between Jon and Daniel on
* 9/17/2021 and deemed the best choice for the moment. In the
* future we might convert this to a helper method that doesn't
* require custom SQL each place it is used - but we really
* shouldn't do full table locks as a matter of practice.
*
* Daniel Hazelbaker 9/17/2021
*/
// Initiate a full table lock so nothing else can query data,
// otherwise they might get a count that will no longer be
// valid after our transaction is committed.
rockContext.Database.ExecuteSqlCommand("SELECT TOP 1 Id FROM [RegistrationSession] WITH (TABLOCKX, HOLDLOCK)");
// Try to find the session to renew, if we can't find it then
// return a failure indication.
registrationSession = registrationSessionService.Get(sessionGuid);
if (registrationSession is null)
{
return(false);
}
// Attempt to get the context that describes the registration
// and the number of available slots.
var context = registrationService.GetRegistrationContext(registrationSession.RegistrationInstanceId, out var errorMessage);
if (errorMessage.IsNotNullOrWhiteSpace())
{
return(false);
}
// Check if the session has expired already before we set the new
// expiration window.
var wasExpired = registrationSession.ExpirationDateTime < RockDateTime.Now;
// Set the new expiration
registrationSession.ExpirationDateTime = context.RegistrationSettings.TimeoutMinutes.HasValue
? RockDateTime.Now.AddMinutes(context.RegistrationSettings.TimeoutMinutes.Value)
: RockDateTime.Now.AddDays(1);
// If the session was expired then the number of reserved spots
// might no longer be valid. Check if there are fewer spots
// actually available and update the count.
if (wasExpired && context.SpotsRemaining.HasValue)
{
if (context.SpotsRemaining.Value < registrationSession.RegistrationCount)
{
registrationSession.RegistrationCount = context.SpotsRemaining.Value;
}
}
// Persist the new session information to the database.
rockContext.SaveChanges();
return(true);
});
return(wasRenewed ? registrationSession : null);
}
}
/// <summary>
/// Creates or update a registration session. This method operates
/// inside a database lock to prevent other sessions from being
/// modified at the same time.
/// </summary>
/// <param name="sessionGuid">The session unique identifier.</param>
/// <param name="createSession">The method to call to get a new <see cref="RegistrationSession"/> object that will be persisted to the database.</param>
/// <param name="updateSession">The method to call to update an existing <see cref="RegistrationSession"/> object with any new information.</param>
/// <param name="errorMessage">The error message.</param>
/// <returns>The <see cref="RegistrationSession"/> that was created or updated; or <c>null</c> if an error occurred.</returns>
public static RegistrationSession CreateOrUpdateSession(Guid sessionGuid, Func <RegistrationSession> createSession, Action <RegistrationSession> updateSession, out string errorMessage)
{
using (var rockContext = new RockContext())
{
var registrationSessionService = new RegistrationSessionService(rockContext);
RegistrationSession registrationSession = null;
string internalErrorMessage = null;
rockContext.WrapTransactionIf(() =>
{
/*
* This is an anti-pattern. Do not just copy this and use it
* as a pattern elsewhere. Discuss with the team before trying
* to use this anywhere else.
*
* This single use-case was discussed between Jon and Daniel on
* 9/17/2021 and deemed the best choice for the moment. In the
* future we might convert this to a helper method that doesn't
* require custom SQL each place it is used - but we really
* shouldn't do full table locks as a matter of practice.
*
* Daniel Hazelbaker 9/17/2021
*/
// Initiate a full table lock so nothing else can query data,
// otherwise they might get a count that will no longer be
// valid after our transaction is committed.
rockContext.Database.ExecuteSqlCommand("SELECT TOP 1 Id FROM [RegistrationSession] WITH (TABLOCKX, HOLDLOCK)");
var registrationService = new RegistrationService(rockContext);
// Load the registration session and determine if it was expired already.
registrationSession = registrationSessionService.Get(sessionGuid);
var wasExpired = registrationSession != null && registrationSession.ExpirationDateTime < RockDateTime.Now;
var oldRegistrationCount = registrationSession?.RegistrationCount ?? 0;
// If the session didn't exist then create a new one, otherwise
// update the existing one.
if (registrationSession == null)
{
registrationSession = createSession();
registrationSessionService.Add(registrationSession);
}
else
{
updateSession(registrationSession);
}
// Get the context information about the registration, specifically
// the timeout and spots available.
var context = registrationService.GetRegistrationContext(registrationSession.RegistrationInstanceId, out internalErrorMessage);
if (internalErrorMessage.IsNotNullOrWhiteSpace())
{
return(false);
}
// Set the new expiration date.
registrationSession.ExpirationDateTime = context.RegistrationSettings.TimeoutMinutes.HasValue
? RockDateTime.Now.AddMinutes(context.RegistrationSettings.TimeoutMinutes.Value)
: RockDateTime.Now.AddDays(1);
// Determine the number of registrants. If the registration was
// expired then we need all spots requested again. Otherwise we
// just need to be able to reserve the number of new spots since
// the last session save.
var newRegistrantCount = wasExpired
? registrationSession.RegistrationCount
: (registrationSession.RegistrationCount - oldRegistrationCount);
// Handle the possibility that there is a change in the number of
// registrants in the session.
if (context.SpotsRemaining.HasValue && context.SpotsRemaining.Value < newRegistrantCount)
{
internalErrorMessage = "There is not enough capacity remaining for this many registrants.";
return(false);
}
rockContext.SaveChanges();
internalErrorMessage = string.Empty;
return(true);
});
errorMessage = internalErrorMessage;
return(errorMessage.IsNullOrWhiteSpace() ? registrationSession : null);
}
}