Strategies for syncing data with server in PhoneGap [closed]

Let me provide the answer to your question based on my experience related to the sync part as I don’t have enough experience with PhoneGap so will skip the question about PhoneGap local storage v SQLite.

I was wondering if you could point me toward some good resources for this type of syncing. Some recommended libraries?

There are a number of open source projects for syncing the PhoneGap app with the remote server. But you probably have to adjust them for your own needs or implement your own sync functionality. Below I listed some of the open-source projects. You must’ve already aware of them if you’d search the net.

• PhoneGap sync plugin
• Simple Offline Data Synchronization for Mobile Web and PhoneGap Applications
• Synchronize a local WebSQL Db to a server
• Couchbase Lite PhoneGap plugin

Additionally, you might consider the other options but that depends on your server side:

• Microsoft Sync Framework Toolkit (Html5 sample is available)
• OpenSync Framework - platform independent, general purpose synchronization engine

Also, my intent to build it Internet-dependent first, and then add syncing.... Is that a good idea, or am I shooting myself in the foot? Do I need to build it syncing from the start?

I believe the sync functionality is more like an additional module and shouldn’t be tightly coupled with the rest of your business logic. Once you start thinking about testing strategy for your sync you’ll realise it will be easier to test that if your sync facility is decoupled from the main code.

I think you can launch your app as soon as possible with the minimum required functionality without sync. But you’d better think about your architecture and the way you add the sync facility in advance.

To start with, I'm thinking of using UUIDs, rather than sequential integer primary keys. I've also thought about assigning each device an ID that is prefixed on any keys it generates, but that seems delicate. Anyone used either technique? Thoughts?

That depends on your project specifications and specifically your server side. For example, Azure mobile services allow only integer type for the primary keys. Although unique identifiers as primary keys are pretty handy in the distributed systems (has some disadvantages as well).

Related to assigning a device ID – I am not sure I understand the point although I don’t know your project specifics. Have a look at the sync algorithm that is used in our system (bidirectional sync using REST between multiple Android clients and central SQL Server).

What about records edited in multiple places? If two client edit, and then want to sync, you have some ambiguity about merging, like when merging branches in git or other version control systems. How do you handle that? I guess git does it by storing diffs of every commit. I guess you could store diffs? The more I think about this, the more complicated it sounds. Am I over-thinking it or under-thinking it?

This is where you need to think about how to handle the conflict resolution in your system.

If the probability of conflicts in your system will be high, e.g. users will be changing the same records quite often. Then you’d better track what fields (columns) of the records had been modified in your sync and then once the conflict is detected:

1. Iterate through each modified field of the server side record in conflict
2. Compare each modified field of the server record with the relevant field of the client.
3. If the client field was not modified then there is no conflict so just overwrite it with the server one.
4. Else there is a conflict so save the both field’s content into a temporary place for the report
5. At the end of sync produce the report of records in conflict.