Add Quartz Job&Trigger to running Razor Pages application - asp.net

Question

I have a razor pages app that implements Quartz.NET to store jobs in a MySQL Database. The implementation works fine so far, I can connect to the db, store jobs and they are executed at the specified times. The issue I'm having currently is that I need to schedule and execute jobs based on user inputs(without restarting the app) and that I can't get to work. I'm very new to Quartz&Asp.net and I haven't been coding for very long either, so apologies if I've made any stupid mistakes.
I've read somewhere that I shouldn't initialize multiple schedulers so I've tried storing the scheduler object I've got so I can access and use it later. However when I try to access it from another class later then I get a Null reference exception. Tbh, this feels like it shouldn't even work so I'm not surprised it doesn't...can anyone please look at my code below and tell me if this can work? Or is there a better way to do this?
I've found one other solution where they basically create a job on startup that periodically checks a db for new jobs and adds them to the scheduler. I guess that would work, seems a bit clunky, though. Plus it's from 10 years ago so maybe there's a better way today? How to add job with trigger for running Quartz.NET scheduler instance without restarting server?
One other idea I've had was to open(and close) a new app whenever I need to create a job. I'm not sure I like that idea but seems less resource intensive than the recurring job described above. Would that be a viable option?
The code for my current solution:
Scheduler:
//Creating Scheduler
Scheduler = await schedulerFactory.GetScheduler();
Scheduler.JobFactory = jobFactory;
var key = new JobKey("Notify Job", "DEFAULT");
if (key == null)
{
//Create Job
IJobDetail jobDetail = CreateJob(jobMetaData);
//Create Trigger
ITrigger trigger = CreateTrigger(jobMetaData);
//Schedule Job
//await Scheduler.ScheduleJob(jobDetail, trigger, cancellationToken);
await Scheduler.AddJob(jobDetail, true);
}
//Start Scheduler
await Scheduler.Start(cancellationToken);
//Copying the scheduler object into a different class where it's easier to access.
ScheduleStore scheduleStore = new ScheduleStore();
scheduleStore.tempScheduler = Scheduler;
ScheduleStore:
public class ScheduleStore
{
public IScheduler tempScheduler { get; set; }
public ScheduleStore()
{
}
}
runtime Scheduler:
public class RunningScheduler : IHostedService {
public IScheduler scheduler { get; set; }
private readonly JobMetadata jobMetaData;
public RunningScheduler(JobMetadata job)
{
ScheduleStore scheduleStore = new ScheduleStore();
this.scheduler = scheduleStore.tempScheduler;
this.jobMetaData = job;
}
public async Task StartAsync(CancellationToken cancellationToken)
{
IJobDetail jdets = CreateJob(jobMetaData);
if (jobMetaData.CronExpression == "--")
{
ITrigger jtriggz = CreateSimpleTrigger(jobMetaData);
//the next line throws the exception.
await scheduler.ScheduleJob(jdets, jtriggz, cancellationToken);
//It's definitely the scheduler that's throwing the null pointer exception.
}
// the else does basically the same as the if, only with a cron trigger instead of a simple one so I've omitted it.

Answer 1

I see that you are using a hosted service. Have you noticed that Quartz has that support already built-in?
Quartz cannot handle new jobs "new code that runs" dynamically, but triggers for sure. You just need to obtain a reference to IScheduler and then you can add new triggers pointing to existing job or just call scheduler.TriggerJob which will call your job once with given parameters (job data map is powerful feature to pass execution parameters).
I'd advice checking the GitHub repository and its examples, there a specific ones for different features and ASP.NET Core and worker integrations.
Generatlly Quartz already has database persistence support which you can use. Just call scheduler methods to add jobs and triggers - they will be persisted and available between application restarts (and take effect immediately without the need for restart).