Two list synchronization

Question

I'm doing the synchronization between the two lists. IList<Event> GoogleEvents and Table<myEvent> DB.Events;

On google side i'm using this

String Summary,
String Description,
EventDateTime Start,
EventDateTime End,
Event.RemindersData Reminders;

On db side like this

my code is like this

foreach (myEvent item in DB.Events)
{
    if (item.GoogleID == "" || item.GoogleID == null)// i add event my db
    {
        //Add dbEvent to google and save id to googleid column
    }
}

foreach (Event item in myGoogleCalendar.Items)
{
    if (DB.Events.Where(o => o.GoogleID == item.Id).Count() == 0)// i add event google
    {
        //Add googleEvent to dbEvent
    }
    else
    {
        //This event also existing in two server
        myEvent dbEvent = DB.Olaylar.Where(o => o.GoogleID == item.Id).First();
        if(item.Updated.Value == dbEvent.UpdateTime) continue;//Same

        if (item.Updated.Value > dbEvent.UpdateTime)
        {
            //Google event is new 
        }
        else
        {
            //dbEvent is new 
        }

    }

}

There is one big problem : I forgot deletion

Where should I add deleting events part and how ?

Loathly

Answer 1

The problem is not to implement a delete synchronization, but to recognize, whether the event has been deleted in one list or added to the other list.

I recommend not to delete events from the DB.Events list, but to mark them as deleted.

Therefore, you need a flag

bool IsDeleted = false;

in your type myEvent.

In Google list (I assume you use https://developers.google.com/google-apps/calendar/v3/reference/events) you don't have such a flag. So your algorithm needs to be a bit tricky.

So you need the first synchronize from the Google list

foreach (Event item in myGoogleCalendar.Items)
{
    if (DB.Events.Where(o => o.GoogleID == item.Id).Count() == 0)
    {
        // create new DB event from Google event, because since it is 
        // not in the DB.Events list, it has not been deleted there earlier, 
        // else there would be an event with IsDeleted=true
    }
    else
    {
        //This event exists in both
        myEvent dbEvent = DB.Events.Where(o => o.GoogleID == item.Id).First();
        if (dbEvent.IsDeleted)
        {
           // delete Google event, since the flag in DB.Events list shows that 
           // it existed earlier and has been deleted in DB.Events list.
        }
        else
        {
            if(item.Updated.Value == dbEvent.UpdateTime) continue;//Same

            if (item.Updated.Value > dbEvent.UpdateTime)
            {
                // update DB event
            }
            else
            {
                // update Google event
            }
        }
    }
}

Then your synchronize from your DB.Events list

foreach (myEvent item in DB.Events)
{
    if (!item.IsDeleted && string.IsNullOrEmpty(item.GoogleID))
    {
        // Create new Google Event from DB event
    }
    else if (!item.IsDeleted && !string.IsNullOrEmpty(item.GoogleID))
    {
        // Mark DB event as deleted
        item.IsDeleted = true;
    }
}

This works in the scenarios

• You create an event in DB
• You create an event in Google
• You delete an event in DB
• You delete an event in Google

Titograd

Firstly thank you for answer. I thought something like this. And i don't understand else if (!item.IsDeleted && !string.IsNullOrEmpty(item.GoogleID)) block. if an event in my db has googleID isDeleted flag = true; But why don't check is not in google. Indeed i must not modify db. Maybe that will work. But if db is change everything change. – Loathly

If the GoogleID of an event is not null or empty, this shows that it once existed in Google. Since it is no more in Google existing, it has been deleted there, hence it has to be marked as deleted. – Titograd

Answer 2

I created a Gist: https://gist.github.com/ricjac/947991ba96488c640bfe

        // Prepare DTO to delta
        var mergeDict = DeltaExtensions.MergeDictionary(
            sourceIEnum,        //Source
            destinationIEnum,   //Destination
            s => s.SomeIdKey,
            d => d.SomeIdKey);

        // Get the delta between the two
        var mergeDelta = DeltaExtensions.GetMergeDelta(mergeDict);

        // You now have the delta of the two:
        mergeDelta.InsertedOnly
        mergeDelta.DeletedOnly
        mergeDelta.Inserted
        mergeDelta.Updated
        mergeDelta.Deleted

Superintendency

i like it too much, definitely reasonable but a little delayed – Loathly

gist not exists – Kerns