Question

I’m out in the woods with this one: I have a universal, navigation-based app that displays data currently stored in a plist file. In a future release, I want to migrate the database to a JSON file on my server which the app can download to it’s bundle, then parse it. Can anyone suggest a simple light-weight way of checking that the currently stored file in the bundle matches the version hosted on the server? Essentially checking for updates to the db without re-downloading the entire JSON file.

Here’s a snippet of what the beginning of the JSON file currently looks like.

{
"version" : "0.2",
"description" : "1. Corrections to several entries.\n2. Added 21 new departments from Alameda & Fresno Counties.",
"counties" : {............... *Rest of the JSON file here* .....}

My idea was to store the “version” (“0.2”) value to NSUserDefaults and use that value to check against the available JSON file online every time the app launches.

Am I on the right track or is there a better way of doing this altogether?

Thank you

Romeo

Answer 1

You can add the If-Modified-Since header to an instance of NSMutableURLRequest. If the document on the server has changed since that date, you’ll get the data back. If it hasn’t changed, you get a 304 Not Modified and no data.

This is much better than making a HEAD request because in the event of an updated file, you’re only making one request instead of two.