CoreData with multiple databases - ios

Question

I'm building an app that is going to rely on 3 separate .sqlite databases. What methods in my App Delegate am I going to have to edit to allow for this? Right now, my managedObjectContext and managedObjectModel haven't been touched from how the template created them. My persistantStoreCoordinator looks like this:
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
if (_persistentStoreCoordinator != nil)
{
return _persistentStoreCoordinator;
}
NSURL *storeURLConfigA = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:#"dbA.sqlite"];
NSURL *storeURLConfigB = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:#"dbB.sqlite"];
NSURL *storeURLConfigC = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:#"dbC.sqlite"];
// // Pre-load .sqlite db in Project Navigator into app on first run after deleting app
if (![[NSFileManager defaultManager] fileExistsAtPath:[storeURLConfigA path]])
// dbA
{
NSURL *preloadURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"dbA" ofType:#"sqlite"]];
NSError* err = nil;
if (![[NSFileManager defaultManager] copyItemAtURL:preloadURL toURL:storeURLConfigA error:&err])
{
NSLog(#"Error preloading database A - %#",error.description);
}
}
if (![[NSFileManager defaultManager] fileExistsAtPath:[storeURLConfigB path]])
// dbB
{
NSURL *preloadURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"dbB" ofType:#"sqlite"]];
NSError* err = nil;
if (![[NSFileManager defaultManager] copyItemAtURL:preloadURL toURL:storeURLConfigB error:&err])
{
NSLog(#"Error preloading database B - %#",error.description);
}
}
if (![[NSFileManager defaultManager] fileExistsAtPath:[storeURLConfigC path]])
// dbC
{
NSURL *preloadURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:#"dbC" ofType:#"sqlite"]];
NSError* err = nil;
if (![[NSFileManager defaultManager] copyItemAtURL:preloadURL toURL:storeURLConfigC error:&err])
{
NSLog(#"Error preloading database C - %#",error.description);
}
}
// // Put the Configs into the PersistantStoreCoordinator and tie them to their database file
NSError *error = nil;
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSDictionary *options = #{NSSQLitePragmasOption : #{#"journal_mode": #"DELETE"}};
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:#"Config_A" URL:storeURLConfigA options:options error:&error])
{
NSLog(#"Error setting up dbA - %#",error.description);
abort();
}
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:#"Config_B" URL:storeURLConfigB options:options error:&error])
{
NSLog(#"Error setting up dbB - %#",error.description);
abort();
}
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:#"Config_C" URL:storeURLConfigC options:options error:&error])
{
NSLog(#"Error setting up dbC - %#",error.description);
abort();
}
return _persistentStoreCoordinator;
}
Then, I have a single .xcdatamodelID in my mainBundle that has all of my tables/Entities in it, for all three databases. I used XCode's CoreData editor interface to add Configurations Config_A, Config_B, and Config_C, in addition to the Default Configuration. I've moved the Entities into the Configurations for the databases I want them to be in (each Entity should only be in one database).
I run the app and everything runs fine, and I can read and write data without any problem. The problem comes when I view the tables (through the terminal or Firefox's SQLite Manager, for example). All 3 of the databases contain all of the tables, but the tables only have data in the database they are supposed to exist in (there are 0 rows in that table in the other two databases).
Why are all of the tables in each database? How can I get each database to only include the couple tables I want them to have?

Answer 1

You have added all 3 of your databases (NSPersistentStores) to the same NSPersistentStoreCoordinator. Therefore, when you perform a save on a Managed Object Context, the store coordinator distributes those changes to all of its stores. Instead, create a persistent store coordinator for each database, perhaps keeping them in an NSDictionary, with a key #"A" for the A database persistent store coordinator, key #"B" for the B database coordinator, etc. Then when you create a new managed object context, you will have to determine which database (NSPersistentStoreCoordinator) it belongs to. This will allow you to keep your tables/changes separated and prevent all data going into all 3 databases.

Answer 2

I started with what Patrick Goley had in his answer, but I still couldn't get the behavior I was looking for. After reading what he had, I got the idea to just go and break my three databases into totally separate pieces everywhere I could think of doing so, and that seems to be working. If someone needs me to post my whole app delegate I will, but the gist of it is:
I have properties for 3 NSManagedObjectContexts, 3 NSManagedObjectModels, and 3 NSPersistantStoreCoordinators.
I copied the factory methods to create each (which were originally written when I created my app from a template) and hardcoded each to use the appropriate contexts/models/store coordinators.
I have 3 NSSets that holds the table names for it's respective database, and when I want to read from (or save to) a table, I pass the name of that table, and use the NSSets to get the appropriate context/model/store coordinator.
After spending a lot of time reading all the Apple docs and other threads I could find, I feel like it wasn't supposed to be this difficult to support separate databases, but this was the only thing that's actually doing what I want so far. I don't know what I was missing before, but this is working, so it will do for now. If I get more free time in the future I might look into it more and try to figure out the right way, and if I find it I'll update.