iOS - 知道PHP JSON文件何时更新

Question

I have a JSON file which displays data from my MySQL database. I have an app that fetches and stores that data in the app on the first launch. It's stored in CoreData so the user doesn't have to be connected to internet to be able to use the app.

I'd like to update the data if anything has changed in the database. The first method I've been using is storing the total length of the JSON data fetched and then comparing it, but I was wondering if there was a better method to do this.

Could I fetch the modification date of the JSON file? If so, how?

Thanks

Answer 1

Storing the length will still leave you with a place for error, and the data could change but keep the same length, what can be more efficient is to store the checksum of the file in your app and whenever it checks for updates from the server it will compare it with the newly generated file's checksum, if the checksum matches then there is no changes. you can use md5_file for this.

You can also cut bandwidth, please check ETag that could save you some time. http://bitworking.org/news/ETags__This_stuff_matters