Object getting Null seems like deserialization issue in Hangfire

Question

It seems like Hangfire is unable to deserialize my original Scheduler object with all its state, whose Execute method I am calling in BackgroundJob.Enqueue() as shown below:

Scheduler = new FileInFileOut
{
    FileIn = new FileInput()
    {
        FileName = "SampleInput.txt",
        DirectoryPath = @"C:\Users\LENOVO\Desktop\iRule",
        FileFormat = new System.Collections.Generic.Dictionary<string, string>
        {
            {"X", "ParseInt(input.Substring(0, 2))"},
            {"Y", "ParseInt(input.Substring(3, 2))"},
            {"Z", "ParseInt(input.Substring(6, 2))"},
        }
    },
    FileOut = new FileOutput()
    {
        FileName = "SampleOutput.txt",
        DirectoryPath = @"C:\Users\LENOVO\Desktop\iRule"
    },
    Trigger = new FireAndForgetTrigger()
};
BackgroundJob.Enqueue(() => Scheduler.Execute());

The Scheduler is of type IScheduler as shown below:

public interface IScheduler
{
    IEntityBaseDef EntityItemBase { get; set; }
    ITrigger Trigger { get; set; }
    RuleApp RuleApp { get; set; }
    Type JobType { get; set; }
    void Execute();
}

[Serializable()]
[DataContract()]
public abstract class Scheduler : EntityModel, IScheduler
{
    public abstract void Execute();
}

[Serializable()]
[DataContract()]
public class FileInFileOut : Scheduler, IFileInFileOut
{
    private FileInput _fileIn;
    public FileInput FileIn
    {
        get { return _fileIn; }
        set { SetProperty(ref _fileIn, value); }
    }

    private FileOutput _fileOut;
    public FileOutput FileOut
    {
        get { return _fileOut; }
        set { SetProperty(ref _fileOut, value); }
    }

    public override void Execute()
    {
        // ERROR on below line, FileIn object is null 
        var directoryInfo = new DirectoryInfo(FileIn.DirectoryPath); 
        var files = directoryInfo.GetFiles();
        if (FileIn.SearchSubDirectories)
        {
            var directories = directoryInfo.GetDirectories().Flatten(x => x.GetDirectories());
        }
    }
}

My Current Scheduler Publishing Logic:

public void Publish()
{
    if (Scheduler != null)
    {
        var trigger = Scheduler.Trigger;
        if (trigger is IFireAndForgetTrigger)
        {
            BackgroundJob.Enqueue(() => Scheduler.Execute());
        }
        else if (trigger is IDelayedTrigger)
        {
            var delayedTrigger = (IDelayedTrigger)trigger;
            BackgroundJob.Schedule(() => Scheduler.Execute(), delayedTrigger.Delay);
        }
    }
}

Is it some kind of deserialization issue? How to identify and correct this issue?

Answer 1

Hangfire does not attempt to store the state of the FileInFileOut object when the Enqueue method is called. It recreates the FileInFileOut object on the worker using a parameterless constructor (or one with parameters using a IOC activator) and then calls the method from your Enqueue expression. This results in the null reference (FileIn / FileOut not set).

You could modify your FileInFileOut method to pass the FileIn and FileOut objects to the Execute method (using a more functional programming approach). This may break other parts of your program so it's probably more appropraite to create a second wrapper class that instantiates the FileInFileOut object for you like:

public class FileInFileOutTasks
{
    public FileInFileOutTasks()
    {

    }
    public void RunExecute(FileIn fileIn, FileOut, fileout)
    {
        var scheduler = new FileInFileOut { FileIn = fileIn, FileOut = fileOut };
        scheduler.Execute();
    }
}

You would then call:

BackgroundJob.Enqueue<FileInFileOutTasks>(x => x.RunExecute(fileIn, fileOut));

and not even create the FileInFileOut object in your code if you didn't want to (just the FileIn / FileOut objects to be passed to the wrapper).