A simple queue for EpiServer

Intro
Queuing is one of the base procedures that you may need as a software developer specially if you are working on web.Think as a task that you want to make sure that it will be done, but you don’t want to suspend your current process for it. for instance you want to send an email in a part of a method or task. you don’t want to wait for email response and you want to try sending it for many times, but you never want your methods to wait for it.
If you are developing on EpiServer, you probably know that there is a dynamic data type which is pretty good for implementing a queue.

Cecilia von Wachenfeldt has a post in here where she describes a simple solution for that. However, I don't like to have both queue and queue item on the same class. From the software architectural view, we have to have a queue class that handles primitive queuing functions (adding to queue, finding unprocessed items, Processing items and deleting them). Then for each type queue, we can just create a corresponding queue-able Item and ask use our queue to handle the object :)

Theory

There has to be a queue, with queue functions. There has to be an enum for the status of the item. Then the queue has to handle everything using each items methods.

This is the list of classes that we need:

1- Queue
2- An interface for Queueable Items (IQueueable)
This interface contains properties that the queue will use like ErrorCount, LastError, Status, etc. and basic methods for processing each special type Like Process().
3- Queueable item which inherits from our IQueueable
This item is simply the object that we want to save into DB. It contains our queue properties/methods and also the required data that you need to use, in order to proceed.

Implementation

Lets say that we want to implement an email queue system, so if the network was down or etc, we won't loose any emails. Our queue and IQueueable are of course the same but for the Queueble Item we have something like this:
First, we have to implement our enum to decide if the item is

Code:

public enum QueueItemState
{
Queued = 0,
Processed = 1,
Retrying = 2,
Failed = 3
}
Then we have to write our Interface:
public interface IQueueableItem
{
int ErrorCount { get; set; }
string LastError { get; set; }
DateTime? QueuedTime { get; set; }
DateTime? CompeletedTime { get; set; }
EnumsQueueItemState State { get; set; }
void AddError(string errorMessage);
bool Process();
Identity Save();
void SetToFaild(string errorMessage);
}

Then we have to implement our interface and add our additional functionality/properties:

(Pay attention to EPiServerDataStore property that cause Episerver to save this item into DynamicData )

Code:

[EPiServerDataStore(AutomaticallyRemapStore = true, AutomaticallyCreateStore = true)]
public class QueueableEmailItem : IDynamicData, IQueueableItem
{
.... [IQueueableItem properties]
public string EmailSubject { get; set; }
public string EmailBody { get; set; }
public string EmailTo { get; set; }
public int? EMailPriority { get; set; }
public bool Process()
{
var priority = EMailPriority.HasValue ? (MailPriority)EMailPriority.Value : System.Net.Mail.MailPriority.Normal;
MailService.Service.Send(EmailSubject, EmailBody, EmailTo, priority, attachedItems);
return true;
}
}

We will need a QueueBase class that handles your queue items. The queue will try to read and execute data that implement IQueueableItem. 

There is only one problem, which is reading items from DB with generics, So I just do the process in the queue base and do the other stuff in the inherited classes using polymorphism.

Code:

public abstract class QueueBase where T : IDynamicData, IQueueableItem
{
public void Proceed()
{
var queue = GetQueuedItems();
if (!queue.Any())
return ;
foreach (var item in queue)
{
try
{
// Exit if the error count is greater or equal to the retry count
if (item.ErrorCount >= RetryCount)
{
item.SetToFaild("RetryCount limit");
continue;
}
if (item.TryProcess())
{
item.State = Enums.QueueItemState.Processed;
item.Save();
continue;
}
item.State = Enums.QueueItemState.Retrying;
item.Save();
}
catch (Exception ex)
{
if (item.State!= Enums.QueueItemState.Failed)
{
item.State = Enums.QueueItemState.Retrying;
}
item.AddError(ex.message);
item.Save();
}
}
}
}

Of course you can have a better code, add logs/ return report/ send email to admin if failed, etc. but this is the simplest code that I could come up with :)

Now we will need to inherit from this class for the emailQueue:

Code:

public class EmailQueue : QueueBase<QueueableEmailItem>
{
public Identity AddToQueue(string to, string emailSubject, string body, MailPriority mailPriority = MailPriority.Normal)
{
var item = new QueueableEmailItem
{
EmailTo = to,
EmailSubject = emailSubject,
QueuedTime = DateTime.Now,
State = Enums.QueueItemState.Queued,
ErrorList = new List<string>(),
EmailBody = body,
EMailPriority = (int)mailPriority
};
return item.Save();
}
protected override List<QueueableEmailItem> GetQueuedItems()
{
var store = typeof(QueueableEmailItem).GetStore();
var query = (
from item in store.Items<QueueableEmailItem>()
where item.State == Enums.QueueItemState.Queued || item.State == Enums.QueueItemState.Retrying
select item);
return query.ToList();
}
}