Strange behaviour when inserting data into core-data - ios

Question

Edit 1
While I understand that for this particular scenario (and other alike) I could use the mapping editor alone to migrate my store correctly so that the values in the persistent store don't jump around, but that's not a solution to my current problem but only avoids addressing the root of the problem. I am keen on sticking with my custom migration policy as this will give me a lot of control through the migration process, especially for future scenarious where setting up a custom migration policy will work for me. This is for a long term solution and not just for this scenario.
I urge you to try and help me solve the current situation at hand rather than diverting me to lightweight migration or advising me to avoid using a migration policy. Thank you.
I really do look forward to sorting this out and your valuable input/ideas on what I could do to fix this problem.
What I have done:
I have a migration policy set up so that the source data can be copied into the new destination data from version 1 of the core model to version 2.
This is the migration policy:
- (BOOL)createDestinationInstancesForSourceInstance:(NSManagedObject *)sInstance entityMapping:(NSEntityMapping *)mapping manager:(NSMigrationManager *)manager error:(NSError **)error {
// Create the product managed object
Product *newProductInstance = [NSEntityDescription insertNewObjectForEntityForName:[mapping destinationEntityName]
inManagedObjectContext:[manager destinationContext]];
NSString *productCode = [sInstance valueForKey:#"productCode"];
NSNumber *productPrice = [sInstance valueForKey:#"productPrice"];
[newProductInstance setProductCode: productCode];
[newProductInstance setProductPrice:productPrice];
/**
The previous old product entries didnt have anything for the last attribute,
where as the new instances of product entity should have a default value of YES.
*/
[newProductInstance setProductPriceNeedsUpdating:[NSNumber numberWithBool:YES]];
/*
A test statement to make sure the destination object contains the correct
values int he right properties:
Product description: <NSManagedObject: 0xb983780> (entity: Product; id: 0xb9837b0 <x-coredata:///Product/t97685A9D-09B4-475F-BDE3-BC9176454AEF6> ; data: {
productCode = 9999;
productPrice = "2.09";
productPriceNeedsUpdating = 1;
})
*/
NSLog(#"Product description: %#", [newProductInstance description]);
// Set up the association between the old source product and the new destination Product for the migration manager
[manager associateSourceInstance:sInstance
withDestinationInstance:newProductInstance
forEntityMapping:mapping];
return YES;
}
So even though the tested properties show the correct values in runtime, the resultant values saved in the data model store is incorrect as seen in the snapshots.
Here is a comparison from version 1 to version 2 of the data store.
Version 1: Correct
to Version 2: Which is now storing the values incorrectly.
The expected output should have the Product price inserted into the productPrice field and not in the ProductPriceNeedsUpdating field which should actually only have boolean values.
Can anyone help me understand what I am doing wrong, or explain whats happening here?
UPDATE 1 - Here are my entity mappings:
Update 2 - 20/aug/2014 01:02 GMT
When I remove the attribute ProductPriceLastUpdated of type date from version 1, and remove the attribute ProductPriceNeedsUpdate of type boolean in version 2, leaving only the two attributes that both match in version 1 and 2, then everything works. Even though I can leave it here and move on, I cant ignore the users that are currently using version 1 of the database which does have that pointless ProductPriceLastUpdated attribute which I need the type converted to boolean and also have the name changed to ProductPriceNeedsUpdate. Thats when things start going weird, and the price values are shown in the ProductPriceNeedsUpdate field instead of the productPrice field.
I hope someone can address the original problem and tell me why it is that the entityMapping, or more so, property mapping is not being saved properly?
Update 3 - EntityMapping and properties:
Version 1
Version 2

Answer 1

For your scenario there is no need for a migration policy. You can just use the mapping model and do the following:
Map the non-changing entities to each other. In the mapping model editor it should say something like A productCode | $source.productCode. This is already filled in for you.
The attribute to be dropped (productPriceLastUpdated) should not appear at all because when you created the mapping model you specified the source and destination models. As the destination model does not contain this attribute, it won't show up.
Where the new boolean attribute productPriceNeedsUpdating is shown, enter '1' for the "Value Expression" (this is equivalent to #YES). It should look like this:
A productPriceNeedsUpdating | 1
Rather than define a policy, you can now just call
migrateStoreFromURL:type:options:withMappingModel:toDestinationURL:
destinationType:destinationOptions:error
You can do very complex operations by just using the mapping model editor.
Your screen shots are from the model editor. Make sure you get familiar with the mapping editor.