Load data into core-data schema

Question

I am implementing a navigation-based application. The user will drill down to the node of interest. I am using Core Data, mostly because I want to try it out. How do I load the database initially? Should I write custom code that loads the database initially, or is there some tool to do it for me ?

Answer 1

Currently as far as I know you have to write custom code to populate the database.

This does seem like a downside, I'd really like to see a tool for batch (shell) pre-population of data sources meant to be used by CoreData.

Answer 2

There is no automatic (i.e. built-in) method for importing data into a Core Data context. I suspect that this is because Core Data is really an object graph management framework (that just happens to be able to persist that object graph to disk) and the mapping between data and object instances necessarily depends on the schema (and so will require at least some code). If you already have the data in an other format, you should read the section of the Core Data pRogramming Guide on importing data into a Core Data context. If you don't already have the data in an other format, you will have to write code either way (to generate an intermediate format or to populate the context directly). Finally, although it is not really a public API, the Core Data XML format is pretty easy to work with by hand or using any number of XML-based tools. Depending on the complexity of your data, you may be able to reverse-engineer the XML schema enough to generate an XML-backed persistent store. You could then migrate this store to an SQLite persistent store and you're on your way.

Answer 3

Here's a simple way to preload the Core Data store using plists.

Make a property list containing an array of dictionaries. Make the keys of each dictionary correspond to the keys of your managed object.

Then, call this method the first time the app launches:

- (void)loadDataFromPropertyList {
    NSString *path = [[NSBundle mainBundle] pathForResource:@"someFile" ofType:@"plist"];
    NSArray *items = [NSArray arrayWithContentsOfFile:path];

    NSManagedObjectContext *ctx = self.managedObjectContext;

    for (NSDictionary *dict in items) {
        NSManagedObject *m = [NSEntityDescription insertNewObjectForEntityForName:@"TheNameOfYourEntity" inManagedObjectContext:ctx];
        [m setValuesForKeysWithDictionary:dict];
    }

    NSError *err = nil;
    [ctx save:&err];

    if (err != nil) {
        NSLog(@"error saving managed object context: %@", err);
    }
}

Call loadDataFromPropertyList the first time the app launches by including the following code in the implementation of application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];  
if (![defaults objectForKey:@"firstRun"])
{
    [defaults setObject:[NSDate date] forKey:@"firstRun"];
    [[NSUserDefaults standardUserDefaults] synchronize];
    [self loadDataFromPropertyList];
}