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I have an Order which has a "to-many" relationship with Units. When I try to log the units (NSSet) in Order, I get a fault error:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Order" inManagedObjectContext:mainContext]; [fetchRequest setEntity:entity]; NSArray *fetchedObjects = [mainContext executeFetchRequest:fetchRequest error:nil]; for (Order *order in fetchedObjects) { NSLog(@"%@", [order units]); break; } [fetchRequest release]; results in:
Relationship 'units' fault on managed object (0x6d9dd00) <Order: 0x6d9dd00> (entity: Order; id: 0x6d88e40 <x-coredata://97A3F3D5-ABA7-499A-A460-5E25CF49C528/Order/p1> ; data: { composition = Hemlock; condition = ""; consignee = ""; consigneeCompanyName = ""; contactAlternatePhone = ""; contactEmail = ""; contactFirstName = ""; contactLastName = ""; contactPhone = ""; customer = "Havard Empire"; customerCompanyName = ""; customerNotes = ""; dateDue = "1/13/2012 12:00:00 AM"; dateEntered = "1/6/2012 12:00:00 AM"; dateOrdered = "1/6/2012 12:00:00 AM"; deliveryAddress1 = ""; deliveryAddress2 = ""; deliveryCity = ""; deliverySpecialInstructions = ""; deliveryState = ""; deliveryZip = ""; depth = 01; detail = ""; freightRate = ""; grade = Cull; instructionsDirectionsNotes = ""; lastUpdated = "1/6/2012 3:00:43 PM"; length = 01; location = "Lucedale, ms"; matsPerLoad = ""; memoLineNotes = ""; notes = ""; orderID = 201205134922479; orderNumber = 01062012; pUP = Cable; pricePerItem = ""; purchaseOrderNumber = ""; pushToQuickBooks = True; quantity = 0; quickbooksCompany = 1; salesman = "Accounting Adj"; separateRate = False; taxRate = ""; totalLoads = ""; type = "2ply Mat"; units = "<relationship fault: 0x6dacf20 'units'>"; vendorID = 10; width = 01; }) The units aren't printed. It says "<relationship fault: 0x6dacf20 'units'>";
Also, why is it printing the entire object when I only want units?
600
In Core Data, faults are placeholders, or “unrealized objects”. They are small objects which refer to other NSManagedObjects, which are fetched into memory only as needed. This faulting mechanism is designed to enhance performance and reduce memory use.
Inverse relationships enable Core Data to propagate change in both directions when an instance of either the source or destination type changes. Every relationship must have an inverse. When creating relationships in the Graph editor, you add inverse relationships between entities in a single step.
Core Data is designed to work in a multithreaded environment. However, not every object under the Core Data framework is thread safe. To use Core Data in a multithreaded environment, ensure that: Managed object contexts are bound to the thread (queue) that they are associated with upon initialization.
Faulting reduces your application's memory usage by keeping placeholder objects (faults) in the persistent store. A related feature called uniquing ensures that, in a given managed object context, you never have more than one managed object to represent a given record.
This isn't an error - it is a feature of Core Data called 'faulting'. Here is Apple's description:
Faulting reduces the amount of memory your application consumes. A fault is a placeholder object that represents a managed object that has not yet been fully realized, or a collection object that represents a relationship:
A managed object fault is an instance of the appropriate class, but its persistent variables are not yet initialized. A relationship fault is a subclass of the collection class that represents the relationship. Faulting allows Core Data to put boundaries on the object graph. Because a fault is not realized, a managed object fault consumes less memory, and managed objects related to a fault are not required to be represented in memory at all.
If you want to see each Unit object then you will have to specifically access them. Try the following:
for (Order *order in fetchedObjects) { for (Unit *unit in [order units]) { NSLog(@"%@", unit); //I am not at a computer, so I cannot test, but this should work. You might have to access each property of the unit object to fire the fault, but I don't believe that is necessary. } } In order to see all the objects of a "to-many" relationship, you can call it with the allObjects method of the relationship's NSSet.
In your specific case, the code to print all the Units of the first Order in fetchedObjects would be like this:
for (Order *order in fetchedObjects) { NSLog(@"%@", [order.units allObjects]); break; } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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