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I'm starting my first PhoneGap project, using AngularJS. It's a database driven app, using a REST API as the backend. To start with, I'm not going to store data locally at all, so it won't do much without Internet.
However, I would eventually like to have it store data locally, and sync when Internet is available, since I know I personally disable the Internet connections on my phone at times (air planes, low battery), or have no bars. I was wondering if you could point me toward some good resources for this type of syncing. Some recommended libraries? Or perhaps some discussions of the pitfalls and how to circumnavigate them. I've Googled a bit, but I think right now, I don't know the questions to ask.
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 had someone suggest building the app as local-only first, rather that the Internet-only part first, which has a certain logic to it. The remote storage is kind of important to me. I know the decision there has a lot to do with my goals for the app, but from the stand point of building this, with the eventual goal being local storage + Internet storage, and two-way syncing, what's going to be easier? Or does it even make a difference?
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?
I guess I need a good system to tell what data's been synced. On the client side, I guess any records that get created/edited, can be flagged for syncing. But on the server-side, you have multiple clients, so that wouldn't work. I guess you could have a last_updated timestamp, and sync everything updated sync the last successful sync.
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?
What about client side storage? I've thought about SQLite, or the PhoneGap local storage thing (http://docs.phonegap.com/en/1.2.0/phonegap_storage_storage.md.html). Recommendations? The syncing will be over a REST API, exchanging JSON, so I was thinking something that actually stores the data as JSON, or something JSON-like that's easy to convert, would be nice. On the other hand, if I'm going to have to exchange some sort of data diff format, maybe that's what I need to be storing?
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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.
Additionally, you might consider the other options but that depends on your server side:
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:
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