Design discussion: Handling conflicts in offline services

[adrianhall]

I’m wondering about improving the conflict handling in the offline “PushAsync” code. Right now, you have to check the PushResult and divine what to do based on the results. This is less than ideal.

My thought is to provide something on the PushOptions - something like

Func<TEntity, TEntity, TEntity> OnConflictHandler;

Let’s say you wanted to use a “last update wins”, you could do something like

TEntity MyConflictHandler(TEntity clientEntity, TEntity serverEntity)
  => clientEntity.UpdatedAt > serverEntity.UpdatedAt ? ClientEntity : serverEntity; 

PushOptions options = new() 
{
    OnConflictHandler = MyConflictHandler;
}

The conflicts would then be handled “in-push-operation” rather than after the fact, with no additional operations afterwards - just the single “force” operation to get the client entity up to the server if necessary. Nor would you need to deal with the operations queue.

Wondering:

1. Do you do much UI work to handle conflicts, or is it generally “accept client” or “accept server”?
2. Do you need an async OnConflictHandler? What would you do that requires async?
3. Does the design make sense to everyone? Would you use it? Would you like to see something else?

Appreciate the design discussion with the community!

[atexinspect]

Hi Adrian,
While using your previous sync package I removed the conflict option from the user and defaulted to 'Server wins'. I found if the user is given a choice they always choose themselves as the conflict winner which is not always the best option. An option of 'Server wins' would be a great feature.

Paul.