I have been at this single task for several days trying to get the relationships between core data entities working. I have achieved this but now I need to change it so that the new attribute value has its relationship added to an existing object. It is a 1 - to - many database.
I am not sure how to add a relationship to a object that already exists. So in the new object that is getting added to RoutineDetail, how would I create the relationship to the object that already exists in the routine Entity?
I have looked at several examples all showing how to add relationships to newly added objects but I need it so the new object in RoutinesDetails has a relationship with the value that already exists in Routines.
The value of Routines is held in a string called RoutineText
rout is the NSmangedObject for the entity Routines
routDet is the NSmanagedObject for the entity RoutinesDetails
I have left the commented out code that allows me to add a relationship when both new objects are created.
This is the last thing I have to do in my project but it is driving me insane. I will be eternally grateful for the fix here. Any advice will be appreciated as this is the best knowledge portal there is. Thank You.
NSManagedObjectContext *context = [self managedObjectContext];
// Create a new device
ExcerciseInfo *info = [_fetchedResultsController objectAtIndexPath:indexPath];
//rout = [NSEntityDescription insertNewObjectForEntityForName:#"Routines" inManagedObjectContext:context];
routdet = [NSEntityDescription insertNewObjectForEntityForName:#"RoutinesDetails" inManagedObjectContext:context];
//Add attribute values
//[rout setValue: RoutineText forKey:#"routinename"];
[routdet setValue: info.name forKey:#"image"];
//Create Relationship
[rout addRoutinedetObject:routdet];
Your main problem statement is, I think, here:
I need it so the new object in RoutinesDetails has a relationship with the value that already exists in Routines.
I presume your data model looks like this:
Routine <----> RoutineDetail
i.e. every one routine has one routine detail (one-to-one relationship).
But this does not really make any sense. You could simply include the attributes of RoutineDetail in the Routine entity.
Instead of
desiredValue = routineDetail.routine.value;
you would simply have
desiredValue = routineDetail.value;
Also, please note that your code has a number of problems. The first line is completely unnecessary, just use self.managedObjectContext. Additionally, against the convention you are using Capital initials for variables. Those should be reserved for class names. Your method to add the relationship also does not look right.
You can add a relationship like this, without a method call:
routineObject.detail = detailObject;
Related
Platform
iOS 10, Xcode 8.3.3
Background
I have built a Notes application that takes advantage of Core Data and I'd like to use this app in my next application, which will also use Core Data. For simplicity, lets call my next application, "ListApp", and my notes application, "NotesApp". This ListApp has list items each of which can have one or more notes.
Here's what I've done so far:
Removed all unnecessary files from the NotesApp and compiled a "NotesApp Framework".
Linked the NotesApp Framework to the ListApp.
Designed the Core Data Model for ListApp. Specifically, I created an entity called "ListItem" and an entity called "Note". The ListItem has a to-many relationship with the Note (one list item can have multiple notes). The Note entity contains a "noteID" field to reference the note in the NotesApp model and, of course, the inverse relationship.
Problem
I need to form a "relationship" between an entity in the ListApp model and an entity in the NotesApp model.
I've researched configurations and that seems to be more for storing objects in the same model to different persistent stores unless there's something I'm missing. So, that doesn't help.
Then, I found that fetched properties can be used to form weak relationships between multiple stores. So, that doesn't help either.
Next, I found in the documentation that there's a method called NSManagedObjectModel.mergedModel(from:) so I'm assuming this is possible. Or maybe that's only for migration?
That's where I'm stuck.
Reason
I'd rather not redesign everything in the NotesApp model in to the ListApp model. I prefer to keep everything separate.
Questions
Is there a way to form a relationship between two entities in different models? Should I just add a function in the ListItem entity class to fetch the notes in the NotesApp model manually? Am I even going down the right path or is there a better option?
NOTE: What I mean by "relationship" is the ability to call on a property in the ListItem entity to fetch the notes and somehow "relate" specific notes to a specific ListItem.
P.S. If you know of any pitfalls, have any general advice, or know of any reading material please feel free to let me know.
Also, I've been researching this topic for a couple of hours and I can't seem to find anything about it. I'm assuming that's either because it's not possible, it's a terrible practice, or I'm not using the right keywords.
If anyone needs any more information feel free to let me know!
I think you're saying your bundle will have one model that contains the List entity and another that contains the Note entity. You can merge and tweak managed object models, as you suggested, and use the resulting managed object model which you have in code.
If you're creating your Core Data stack in code (that is, you are not using the new NSPersistentContainer), it is easy to splice in a custom managed object model.
If you are using NSPersistentContainer, you'd have to subclass it and override managedObjectModel(). I can't find any documentation saying you can't do that, but I wouldn't bet on that.
If you're document-based, overriding UIDocument's managedObjectModel should work.
To create your custom managed object model, merge your models using NSManagedObjectModel.mergedModel(from:). Then, get the Note and List entity decriptions, get the properties of each, mutate, add your new relationships, then set them back into the model. You would only do this on the first run; cache your custom managed model to a ivar for subsequent runs.
Hmmmm. What I've just described, essentially tearing apart, tweaking and reassembling that managed object model, is going to be quite a few lines of code. If this is a really just a simple "notes and lists" app, and if these are the only these two entities, it would probably be less code to ditch those .mom files and create the whole managed object model from scratch, in code. It's not that hard. Put on your Objective-C glasses and look at the managedObjectModel() function in main.m of Apple's old Core Data Utility sample project.
Alright, so turns out I had a slight misunderstanding of the Core Data Stack but, this is an extremely simple task. I was able to get this to work very easily based on some research and #Jerry Krinock's answer.
Create a framework containing the needed files from the NotesApp.
Link the framework to the ListApp.
Grab mutable references to the ListApp and NotesApp NSManagedObjectModel.
Programmatically add a NSRelationshipDescription between the ListItem entity in the ListApp Model and the Note entity in the NotesApp Model (and vice versa for the inverse).
Create a NSManagedObjectModel by merging the ListApp and NotesApp models.
NOTE: As #Jerry Krinock mentioned this only needs to be done once since we are merging the two models together and storing them in the same persistent store. This is the same as doing it through the CoreData Model Builder UI except programmatically since it doesn't support referencing entities from separate models (at least not that I know of or could find).
References:
Core Data Programming Guide
Core Data stack
Universal Cocoa Touch Frameworks for iOS8 – (Remix)
Adding relationships in NSManagedObjectModel to programmatically created NSEntityDescription
Objective-C:
NSManagedObjectModel * listModel = [[[NSManagedObjectModel alloc] initWithContentsOfURL:[self listModelURL]] mutableCopy];
NSManagedObjectModel * notesModel = [[[NSManagedObjectModel alloc] initWithContentsOfURL:[self notesModelURL]] mutableCopy];
NSEntityDescription * listEntity = [listModel.entitiesByName objectForKey:NSStringFromClass([JBListItemMO class])];
// The framework name is prepended to the class name. Remove it before getting the note's entityDescription.
NSString * noteClassName = [NSStringFromClass([JPSNoteMO class]) componentsSeparatedByString:#"."].lastObject;
NSEntityDescription * noteEntity = [notesModel.entitiesByName objectForKey:noteClassName];
NSRelationshipDescription * whichListRelationship = [[NSRelationshipDescription alloc] init];
whichListRelationship.minCount = 0;
whichListRelationship.maxCount = 1;
whichListRelationship.optional = NO;
whichListRelationship.name = #"whichList";
whichListRelationship.destinationEntity = listEntity;
whichListRelationship.deleteRule = NSNullifyDeleteRule;
NSRelationshipDescription * notesRelationship = [[NSRelationshipDescription alloc] init];
notesRelationship.ordered = NO;
notesRelationship.maxCount = 0;
notesRelationship.minCount = 0;
notesRelationship.optional = YES;
notesRelationship.name = #"notes";
notesRelationship.destinationEntity = noteEntity;
notesRelationship.deleteRule = NSCascadeDeleteRule;
notesRelationship.inverseRelationship = whichListRelationship;
whichListRelationship.inverseRelationship = notesRelationship;
listEntity.properties = [listEntity.properties arrayByAddingObject: notesRelationship];
noteEntity.properties = [noteEntity.properties arrayByAddingObject: whichListRelationship];
self.managedObjectModel = [NSManagedObjectModel modelByMergingModels:#[listModel, notesModel]];
I'll post the Swift 3 code when I've finished converting my CoreDataStack class.
How to update the data if it is already exist in the database, when we click on the button save?
Thanks for your help.
- (IBAction)save:(id)sender {
NSManagedObjectContext *context = [self.recipe managedObjectContext];
if (!self.material) {
self.material = [NSEntityDescription insertNewObjectForEntityForName:#"Material" inManagedObjectContext:context];
[self.recipe addMaterialsObject:self.material];
self.material.displayOrder = [NSNumber numberWithInteger:self.recipe.materials.count];
}
[self.parentViewController dismissViewControllerAnimated:YES completion:nil];
}
That depends on you how you define instances of your Material entity to be equal. For example, is 100g flour and 200g flour the same (they should be, and you should find a way to separate quantity from ingredient...).
You can implement a method isEqualToMaterial:(Material*)otherMaterial and compare the essential attributes, like name and perhaps category. Before inserting a new entity object you could instead use the existing one.
However, from your code I see that you store a displayOrder in the material object, which depends on the number of materials in the recipe. That would presumably overwrite any existing displayOrder - so your current setup with multiple largely identical materials, while not ideal, might be what you want.
Maybe you should re-think your data model setup and devise a way where the user can choose from a list of ingredients before starting to type in his own.
I'm trying to learn how to use core data, but i got stuck on creating a relationship between two entities, i dont know if i'm looking at this at wrong angle, but basically, i have two Entities: "Listas" and "Tarefas". In my xcdatamodeld, i created a one-to-many relation between the objects, i just dont know how to set the correct relation when adding a "Tarefa".
To my question more clear, here is a image of what i have:
When adding a "Tarefas", object how do i relate it, with the passed "Listas" object?
Thank you!
It works the same as any other object attribute.
If you do not have custom NSManagedObject subclasses,
Listas *myListas = // passed in
Tarefas *newTarefas = [NSEntityDescription insertNewObjectForEntityForName:#"Tarefas" inManagedObjectContext:myManagedObjectContext];
[newTarefas setValue:myListas forKey:#"tarefaLista"];
If you do have custom NSManagedObject subclasses,
Listas *myListas = // passed in
Tarefas *newTarefas = [NSEntityDescription insertNewObjectForEntityForName:#"Tarefas" inManagedObjectContext:myManagedObjectContext];
[newTarefas setTarefaLista:myListas];
Keep in mind that since you have inverse relationships configured correctly, you only need to make the assignment on one side of the relationship. Core Data will make sure that the other side is also set. So above, I'm only setting a value for tarefaList, but the listaTarefa also gets a new value.
You could go:
Listas* l = //Your passed Listas
Terafas* t = //create your new Terafas
t.terafaLista = l;
It would be easier not to call your entities in a plural form (instead of Listas call it Lista). your code would make more sense.
As #TomHarrington mentioned, your inverse relationship will be automatically maintained.
I imagine that people will se this in future, so just in case, this is the code to filter the data based on the relationship between the two objects.
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"SELF IN %#", self.currentListas.listaTarefa];
[fetchRequest setPredicate:predicate];
self.currentListas is the Lista object passed by the segue.
Long question---thanks in advance for your time. After saving new managed objects, I am finding them added to a relationship on another object in my core data database---one for which my code calls no setter method and that has no inverse relationship. I have pored over the code and used logs to isolate the occurrence the best I can, but I'm encountering bizarre behavior I cannot explain (or fix).
More specifically:
I have an entity called PendingSyncTracker. It simply has one relationship, objectsToSync. I have not yet added any line in my code to call a setter method on this relationship. It is a to-many relationship. It points to BaseEntity. For the "Inverse" option, I have selected "No Inverse Relationship."
When I load a particular table view, 3 objects are downloaded from a server and then parsed into managed objects and saved. By the time the table view begins loading cells, 2 of those 3 objects will mystifyingly be present in the objectsToSync relationship.
I have used NSLog all over my code to figure out exactly when these objects can first be found as members of the objectsToSync set.
NSSet *objectsToSync = [[[SyncEngine sharedEngine] fetchClassNamed:#"PendingSyncTracker" withPredicates:nil][0] valueForKey:#"objectsPendingSync"];
NSLog(#"PendingSyncTracker objectsToSync set (%lu objects): %#", (unsigned long)[objectsToSync count], objectsToSync);
The answer to when they first appear in the set actually varies depending on where I do/don't place those 2 lines of code!
The objects are never found on the relationship before the managed object context is saved in the course of saving my 3 new core data objects.
If I don't use those 2 lines till I'm back in the Table View Controller that sent the new objects off to the Sync Engine to be stored locally (where the MOC is accessed and saved), then the log will there reveal that 2 objects have been added to the relationship.
If I use those 2 lines immediately after saving the MOC in the Sync Engine, then the logs will indicate (both there and back in the TVC) that only 1 object has been added to the relationship.
If I use those 2 lines immediately before and after saving the MOC (and back in the TVC), then all 3 logs will reveal that the relationship contains an empty set.
I also have those 2 lines at the beginning of cellForRowAtIndexPath. Regardless of prior logs, that log will always indicate that 2 objects have been added to the relationship.
All 3 of the managed objects that are created in the Sync Engine are stored as entity types that are subEntities of BaseEntity (to which the objectsToSync relationship points). The 2 types that get added to the relationship are each defined to have a reciprocal relationship, but with a different object, not PendingSyncTracker (although the different object is a subEntity of BaseEntity!).
So.. what explains these observations? How are these objects getting added to the relationship?
UPDATE:
- (NSArray*) fetchClassNamed:(NSString*)className withPredicates:(id)parameters;
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:className inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// set predicates
if (!(parameters == nil)) {
[fetchRequest setPredicate:parameters];
}
NSError *error;
NSArray *fetchedResults = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
return fetchedResults;
}
First, what does [[[SyncEngine sharedEngine] fetchClassNamed... do? Just a guess but it is doing something with KVC to set the relationship for you.
Also, you should always, always, always have an inverse relationship. Even if you never use it, Core Data does. Not having an inverse can lead to lots of issues, including but not limited to performance problems and potentially data corruption.
Add an inverse relationship and update your question with what -fetchClassNamed... does.
I am trying to understand Core Data (To-Many) relationship. In the following code, I have two Entities
PeopleList <-->> TransactionDetails
NSManagedObjectContext *context = [self managedObjectContext];
NSManagedObject *personDetails = [NSEntityDescription
insertNewObjectForEntityForName:#"PeopleList"
inManagedObjectContext:context];
[personDetails setValue:[person fullName] forKey:#"name"];
NSManagedObject *transactionDetails = [NSEntityDescription
insertNewObjectForEntityForName:#"TransactionDetails"
inManagedObjectContext:context];
[transactionDetails setValue:[NSNumber numberWithFloat:oweAmount] forKey:#"amount"];
NSError *error;
if (![context save:&error]) {
NSLog(#"Whoops, couldn't save: %#", [error localizedDescription]);
}
Now this code inserts a New Object (row) to the model. What I am confused with is:
1. Don't I have to write code for relating object values in two Entities (PeopleList and TransactionDetails)?
2. If I run this code again and again, It just keep on adding same object in first Entity (PeopleList). How to write for To-Many relationship? What I can get from last few hours of reading is I have to fetch the results, search for that particular object and if it exist then dont insert a new object with same name. But in that case, how will it relate the two entities.
Are your model entities correctly wired in the model editor as far as the to-many relationship is concerned? Have you generated the class files for your entities? If you can answer both questions with yes you create a personlist entity as you did and the details entity too but you need to the details to your personlist. Have a look into the class files for the method name(s).
It won't, because you're not setting the relationships on either of your objects. I don't see where you're setting the PeopleList property of your newly minted TransactionDetail object (sorry, I don't know how you've got the properties named in your model, so I'm just using the class names). So, after creating your transactionDetails object, you'd need to do something like transactionDetails.PeopleList = personDetails, and both relationships would be set at that point; transactionDetails.PeopleList property would point to your personDetails object, and personDetails.TransactionDetails set would contain transactionDetails.
What is your person object, that you're using to set the name from?
On another note, you might want to consider moving all this sort of stuff into subclasses of NSManagedObject; write your own super easy constructors/initializers, etc, for each of your entities. Lots of people never do this, and end up littering their controller code with lots of CoreData boiler plate, which is a mystery to me, because it's what makes using CoreData so nice.