Question

Original question was “I have a sqlite 3 db (a dictionary), that I want to use in a new app. Is there a short cut to creating the core data relationship model, based on the db structure?”

This is how I solved the problem – with lots of help all over the net.

I simplified the DB and that made writing the core data model pretty easy.

I used a Python script from this great site, to manage the conversion.

The script is as follows:

import sqlite3;

inConn = sqlite3.connect('dictold.sqlite')
outConn = sqlite3.connect('dictnew.sqlite')

inCursor = inConn.cursor()
outCursor = outConn.cursor()

maxId = 0
inCursor.execute("select * from lexicon")
for row in inCursor:

    if row[0] > maxId:
        maxId = row[0]

    # Create ZLEXICONENTITY entry
    vals = []
    vals.append(row[3]) # Z_PK
    vals.append(1) # Z_OPT
    vals.append(2) # Z_ENT  
    vals.append(row[0]) # ZIND
    vals.append(row[1]) # ZENGLISH
    vals.append(row[2]) # ZGREEK
    outConn.execute("insert into ZLEXICONENTITY values(?, ?, ?, ?, ?, ?)", vals)


outConn.execute("update Z_PRIMARYKEY set Z_MAX=?", [maxId])

outConn.commit()

Once I had the database built, I had a problem connecting it to the Core Data model. I got a message that the “model did not match the database”.

The solution is to let Core Data create the empty data base from the model, and then have Core Data import the data itself.

I first exported my sqlite database (created with Python) to sql calling the file db.sql (imaginative!). I only exported the data table and the primary key table, not the metadata table. You can also do this at the command line. I used an app called SQLiteManager.

All the code in Core Data is stock stuff except for handling the Persistent Store Controller..

That code is as follows:

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (persistentStoreCoordinator_ != nil) {
        return persistentStoreCoordinator_;
    }


    NSString *storePath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"db.sql"];

    // set up the backing store
    NSFileManager *fileManager = [NSFileManager defaultManager];
    // If the expected store doesn't exist, copy the default store.
    if (![fileManager fileExistsAtPath:storePath]) {
        NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@"dict" ofType:@"sqlite"];
        if (defaultStorePath) {
            [fileManager copyItemAtPath:defaultStorePath toPath:storePath error:NULL];
        }
    }

    NSURL *storeURL = [NSURL fileURLWithPath:storePath];

    NSError *error = nil;
    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return persistentStoreCoordinator_;
}

Many probably know all this, but I had to tough it out for a few days. There are probably easier ways to do this too. But perhaps it will help others..

Answer 1

No.

Core Data cannot infer your model from your existing schema, you will have to create the model and then migrate the store on your own.