It try to remove items from to-many relationship like this:
(application.selectedDiagrams as! NSMutableOrderedSet).removeObjectsInRange(NSMakeRange(1, 2))
mainMOC.save(nil)
After I carry out commands, it seems to work, but latter deleted items appears again. Why?
You are probably running into a Swift versus Objective-C conflict. You are much better off using the standard Core Data add and remove objects methods. Hence, create an array with the objects you would like to remove and then pass it to remove<Type>Objects:.
Related
I'm sorry the title may mislead you, since I'm not so good at English. Let me describe my problem as below (You may skip to the TL;DR version at the bottom of this question).
In Coredata, I design a Product entity. In app, I download products from a server. It return JSON string, I defragment it then save to CoreData.
After sometimes has passed, I search a product from that server again, having some interaction with server. Now, I call the online product XProduct. This product may not exist in CoreData, and I also don't want to save it to CoreData since it may not belong to this system (it come from other warehouse, not my current warehouse).
Assume this XProduct has the same properties as Product, but not belong to CoreData, the developer from before has designed another Object, the XProduct, and copy everything (the code) from Product. Wow. The another difference between these two is, XProduct has some method to interact with server, like: - (void)updateStock:(NSInteger)qty;
Now, I want to upgrade the Product properties, I'll have to update the XProduct also. And I have to use these two separately, like:
id product = anArrayContainsProducts[indexPath.row];
if ([product isKindOfClass:[XProduct class]] {
// Some stuff with the xproduct
}
else {
// Probably the same display to the cell.
}
TL;DR
Basically, I want to create a scenario like this:
Get data from server.
Check existed in CoreData.
2 == true => add to array (also may update some data from server).
2 == false => create object (contains same structure as NSManagedObject from JSON dictionary => add to array.
The object created in step 4 will never exist in CoreData.
Questions
How can I create an NSManagedObject without having it add to NSMangedObjectContext and make sure the app would run fine?
If 1 is not encouragement, please suggest me a better approach to this. I really don't like to duplicate so many codes like that.
Update
I was thinking about inheritance (XProduct : Product) but it still make XProduct the subclass of NSManagedObject, so I don't think that is a good approach.
There are a couple of possibilities that might work.
One is just to create the managed objects but not insert them into a context. When you create a managed object, the context argument is allowed to be nil. For example, calling insertNewObjectForEntityForName(_:inManagedObjectContext:) with no context. That gives you an instance of the managed object that's not going to be saved. They have the same lifetime as any other object.
Another is to use a second Core Data stack for these objects, with an in-memory persistent store. If you use NSInMemoryStoreType when adding the persistent store (instead of NSSQLiteStoreType), you get a complete, working Core Data stack. Except that when you save changes, they only get saved in memory. It's not really persistent, since it disappears when the app exits, but aside from that it's exactly the same as any other Core Data stack.
I'd probably use the second approach, especially if these objects have any relationships, but either should work.
I'm using Realm.io as database and I need a select * from all_tables in Realm.
I mean a method returning an RLMArray, but I have not found anything about this.
I need the class reference, such as Realm Browser.
Thanks.
You can use [realm.schema.objectSchema valueForKey:#"className"] to get an NSArray of all of the RLMObject subclasses used in the Realm.
I don't believe this is possible at the moment. You should request it on github. In the mean time you will have to create your own. First you have to know that an RLMArray can only hold one type so if in these different tables there are different types than you can not do the following. It would be as easy as creating your own method for this. It would consist of getting all objects from each table and just inserting them into the RLMArray; If your tables don't have the same type then you will have to use a NSMutableArray or an NSArray.
I am mapping data using RestKit 0.20 into a Core Data and displaying it in a UITable. I am writing the data, an 'Activity' object, to the mainQueue's ManagedObjectContext and it all works fine. Now I need a second table with Future-Activities and also a third table with Past-Activities. I need a ManagedObjectContext for each table as the sorting is done on the server side. How can I handle this and have persistent data. Is 'newChildManagedObjectContextWithConcurrencyType' what I need to use?
Keep a single store. Use a predicate to filter out the items you want.
If you can download all of the data (and you're happy to do that even though some of it may not be used by the user), and you can tag them for what they are used for then that is an option.
From a RestKit point of view, you can use metadata to tag the items during the mapping process so that you know how they should be used (and then filter on that). This requires that you add a new key to the item - but, if one item could be in all responses this will be problematic because the values would get overwritten.
To use metadata, simply add a new mapping like:
#"#metadata.URL": #"requestURL"
Where #metadata.URL is the URL used to make the request and requestURL is the property on your entity that you can use for filtering. The predicate will check for contains your types ("all_day" "start_time" "end_time").
Quick question, if I want to replace a to-many relationship completely. Do I need to delete all the previous objects, or is that done automatically
newVariable.hasRel = [NSSet setWithSet:newSet];
Where the variable has had some objects in that set, will just replacing it with the new set get rid of the old entities ???
Quick answer: Assigning a new set of related objects does not delete the previously related objects. You have to do that manually.
In the documentation and in the broad literature the generated factory method to delete/remove a subclassed managed object in CoreData for IOS is
(void)removeXXXObject:(NSManagedObject *)value
where XXX is the corresponding relationship or we can use simply removeObject.
In my code I used this:
Data *lastData = [[self sortedPersonDatas] objectAtIndex:0];
[selectedPerson removePersonDatasObject:lastData];
where PersonDatas is a one-to-many relationship to Data managed object from I took the last data (lastData resulted from a sorted array of all data)
But using the first two remove methods and checking the SQL database behind we can find that the actual data is existing just the inverse relationship is null.
To completely delete the data (all attributes and the object) I had to use:
[selectedPerson.managedObjectContext deleteObject:lastData];
The question: which is the better method and is it correct that CoreData leaves the data intact?
removeXXXObject only removes an object from a to-many relationship, but does not delete the object from the store. To do so, you have to indeed use deleteObject - this is the desired behavior. Calling deleteObject will by default also set the corresponding relationships to nil (see https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html#//apple_ref/doc/uid/TP40001857-SW1).