Best practices - synchronize database with external source?

I have a bit of a technical issue that I'm working through that I'd like some advice on. I have an external source for data, it's a JSON string and I need to store the info in my database. The problem is this data can change - new elements can be added, modified, or removed. Whenever these changes happen I need to update the data in my database. This is Java, btw. Code has been simplified for easy reading.

This seems to handle creating and updating. What I haven't figured out is what if an element is deleted from the JSON. How do I tell if it no longer exists and then remove it from my database?

At the start I could get a list of all the elements currently in the database. As I'm looping through the JSON nodes add them to another list. Once i'm done adding new ones loop through both lists and remove elements not found in the first list. I'm just really trying to avoid this second loop. Anyone have any pointers?

Had to tweek it a little bit but works like a charm man, thanks.

Desidero_sl said:

Out of curiosity, what part did you have to tweak?

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Instead of adding the updates and new items to their own maps I just performed the operation right there.

Desidero_sl said:

Ah. I had it set up that way so you could do more efficient batch inserts/updates/deletes, but that works too.

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Humm interesting. My ORM package has a batch function, but I'm dealing with a small number of transactions (~10) at a time. It is on Android, though. I may look into it.