I don't even know how to title this one:
Lets say I have a manufacturer entity and a model entity, with a one-to-many relationship.
Each manufacturer can have multiple models (just using these as an example).
manufacturer has a tableview and its independent fetchedResultsController, then when you press on a manufacturer cell you go to models viewcontroller that also has its own tableview and fetchedResultsController, ofc showing the relevant added models.
Let's say I would like to take one of the models and copy them or cut them into another manufacturer, I was thinking of a method styled like:
-(void)copyThis:(Model*)model toThat:(Manufacturer*)manufacturer
I am grabbing the right manufacturer object and the right model object but how can I implement the insertion of one to another?
To copy
Model *newModel = [NSEntityDescription insertNewObjectForEntityForName:#"Model" inManagedObjectContext:self.context];
newModel.property = model.property; //For every property
model.relationShipName = manufacturer;
[self.context insertObject:copyModel];
To cut
model.relationShipName = manufacturer;
(I assume that you have an xcdatamodeld and have generated an NSManagedObjectSubclass of your Model and Manufacturer entities)
What do you want to achieve with copying? Do you want a 'new' model with the exact parameters added to the other manufacturer, or do you want the relationship to be with the same model object?
Assuming you want to keep a single instance of the Model object:
Manufacturer *fromManufacturer = ...
Model *model = [[fromManufacturer models] objectAtIndex:...];
Manufacturer *toManufacturer = ...
[toManufacturer insertModelObject:model];
if (isCut) [fromManufacturer removeModelObject:model];
To get the insertModelObject and removeModelObject methods automatically, you can use Xcode to generate NSManagedObject subclasses for you automatically. It's under the Editor menu when you're looking at the CoreData Model file. Note that the names of the methods and objects may be different depending on the CoredData model structure and relationship names you've created.
Related
I have made a many-to-many relationship. At first I insert all the data in table 1, the rest of the data isn't available right away.
When the data is available I like to connect it to the right table 1 entries. Should I query table 1 and then set the NSSet with the returned data? Or how would one do this?
To elaborate my question here the example:
[ActivityTable] <<--->> [BannerTable]
At viewDidLoad all the activity are upserted in the ActivityTable. Then the banners from the first activity (first upcoming date) is found from the server.
I got the two (it is always two) banners available but how do I set this?
Used this with help of the answer:
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Banner" inManagedObjectContext:context];
Banner *banner = [[Banner alloc] initWithEntity:entity insertIntoManagedObjectContext:context];
banner.image = shieldDictionary[BANNER_IMAGE];
Assuming you are using the generated NSManagedObject subclasses for your entities...
In your CoreData model each relationship has a name.
Your generated entity classes already contain methods to add/remove relationships you defined in the model. So all you have to do is use one of those methods.
Example:
If the tables are called 'ActivityTable' and 'BannerTable', and the relationship in 'ActivityTable' is called 'banners', then the generated methods look like:
- addBannersObject:(BannerTable *)value;
- removeBannersObject:(BannerTable *)value;
- addBanners:(NSSet *)value;
- removeBanners:(NSSet *)value;
Core Data manages a graph of objects, not tables.
The easiest way to realize many-to-many relationships is to use the dynamically-generated accessors like add<Key>Object: and remove<Key>s:.
For instance:
[anActivity addBannerObject:aBanner];
You can use the data model editor to generate class files for your models which declare these generated methods. You can also use -mutableSetValueForKey: to get a proxy that lets you add and remove objects from a relationship. i.e.:
NSMutableSet *banners = [anActivity mutableSetValueForKey:#"banners"];
[banners addObject:aBanner];
It is obviously less verbose to use the generated methods for each relationship, but it achieves the same thing.
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;
I have 2 distinct core data models in my iOS app. In the first VC, I create a reference to an entity UserDetail in a singleton class I've designed.
After the user leave this VC, I use another core data model, completly different from the first one. I change objectModel, objectContext and persistentStore.
And it seems that after I change to this second core data model I lose the reference to the entity UserDetail that I've created in the beginning.
After the fetch I save the reference like this:
UserAccount *account = [array objectAtIndex:0];
sharedInstance.account = account;
and after changing the core data model whenever I try to access sharedInstance.account it's nil. Should the property be (copy)?
Am I missing something?
Thanks
I'm struggling with some aspects of Core Data, namely setting up a UITableView to list data from a to-many relationship.
I have three entities, Teams, TeamDetails and Players:
In the first view, I list the names of all the teams in the Teams entity, then tapping each cell segues to an intermediate view with buttons to either edit a team's details or edit a team's players. Tapping on a button segues to another UITableView that lists the Team's details or Players.
Listing the TeamDetails works, since it is a one-to-one relationship and a static cell table.
I'm trying to set up a UITableViewController that lists all the players that are associated with the selected team. So I pass the ManagedObjectContext etc to the table view controller via the segue as shown below:
else if ([segue.identifier isEqualToString:#"ShowPlayersSegue"]){
NSLog(#"Setting ShowPlayersTVC as a delegate of EditPlayerTVC");
ShowPlayersTVC *showPlayerTVC = segue.destinationViewController;
showPlayerTVC.delegate = self;
showPlayerTVC.managedObjectContext = self.managedObjectContext;
showPlayerTVC.team = self.team;
showPlayerTVC.player = self.team.playerDetails;
}
So, in my showPlayerTVC I want to get the set of players for that specific team, then have a row for each one that shows the playerName attribute as the cell textlabel.text.
I've been reading tutorials and playing around for ages without getting much success. I think I need to create an array of Player objects from the NSSet, which I can do, but I can't get the UITableview to list the objects. I'm probably missing something fundamental here, but any suggestions would be appreciated.
First, there are some issues with your data model.
The one-to-one to details I do not understand - why not just add attributes to the Team entity? Also, you may want to transform some of these into more flexible relationships, such as a Trainer entity, etc.
Also, your naming is flawed and will lead to programming errors or at least make your code difficult to read. Note the singular / plural confusion. Here is my suggestion for naming your entities / relationships:
Team - players <--------------->> team - Player
To display data in an a table view you should use NSFetchedResultsController. Let the FRC fetch the Player entity and give its fetch request the following predicate:
[NSPredicate predicateWithFormat:#"team = %#", teamObject];
Your segue code is almost correct. Give the new view controller a team attribute and use this in the above predicate of its fetched results controller. You do not need any player or "playerDetails" information (they are linked to the team anyway).
I'm having difficulty with a one to one relationship. At the highest level, I have a one to many relationship. I'll use the typical manager, employee, example to explain what I'm trying to do. And to take it a step further, I'm trying to add a one to one House relationship to the employe.
I have the employees being added no problem with the addEmployeesToManagereObject method that was created for me when I subclassed NSManagedObject. When I select an Employee in my table view, I set the currentEmployee of type Employee - which is declared in my .h.
Now that I have that current employee I would like to save the Houses entities attributes in relation to the current employee.
The part that I'm really struggling with is setting the managedObjectContext and setting and saving the houses attributes in relation to the currentEmployee.
I've tried several things but here's my last attempt:
NOTE: employeeToHouse is a property of type House that was created for
me when I subclassed NSManagedObject
House *theHouse = [NSEntityDescription
insertNewObjectForEntityForName:#"House"
inManagedObjectContext:self.managedObjectContext];
// This is where I'm lost, trying to set the House
// object through the employeeToHouse relationship
self.currentEmployee.employeeToHouse
How can I access and save the houses attributes to the currentEmployee?
since House is setup as an Entity it can be considered a table within the data store. If that truly is the case, you need to setup a 1 to 1 relationship between Employee and House in your data model.
If you have already done so, then it is as simple as calling. Although I'm not as familiar with one to one relationships with Core Data as I am with to-many. In either case, try one of the following
[self.currentEmployee addHouseObject: theHouse];
or
self.currentEmployee.employeeToHouse=theHouse;
then to the save to the managedObjectContext:
NSError *error=nil;
if (![self.managedObjectContext save:&error]{
NSLog(#"Core Data Save Error: %#", error);
}
Also, I'm not sure about your particular situation, but your self.managedObjectContext should already be the same as the one pointed to by self.currentEmployee.managedObjectContext.
Good luck,
Tim