How to use FMDB in background with SQLCipher?

Question

I have some problems to make my queries in the background.

I download a JSON from internet, parse it with Reskit and save an array of objects with FMDB into my sqlite3 database encrypted with SQLCipher.

This is an example:

FMDatabaseQueue *_queueSelect = [FMDatabaseQueue databaseQueueWithPath:[DataBaseController getPathBaseDatos]];

    [_queueSelect inDatabase:^(FMDatabase *db) {

        [db setKey:DATABASE_KEY];

        FMResultSet *existeConsulta = [db executeQuery:sql];
            while([existeConsulta next]) {

                [results addObject:[existeConsulta resultDictionary]];

            }
    }];

I tried to use "inTransaction" and "dispatch_async" but without success.

What is the right way to do this task?

Answer 1

To run this asynchronously, FMDatabaseQueue doesn't do this asynchronous operation for you, but just gives you a framework so that when you interact with this queue from multiple threads, the interaction will be synchronized for you.

So, one would (a) instantiate a single FMDatabaseQueue object for the entire app; and (b) when you want to run something asynchronously, you have to run that from a background dispatch or operation queue.

For example:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT), ^{
    [_queueSelect inDatabase:^(FMDatabase *db) {
        // do your stuff here
    }];
});