So I am building in a hide function into my application. In my settings menu I have a UISwitch that should allow the user to hide themselves. I have created the UISwitch's IBAction like so:
-(IBAction)hideUserToggle:(id)sender {
AppDelegate *newAppDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [newAppDelegate managedObjectContext];
NSManagedObject *newOwner;
NSEntityDescription *entityDesc = [NSEntityDescription entityForName:#"LoggedInUser" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDesc];
NSManagedObject *matches = nil;
NSError *error;
NSArray *objects = [context executeFetchRequest:request error:&error];
newOwner = [NSEntityDescription insertNewObjectForEntityForName:#"LoggedInUser" inManagedObjectContext:context];
if (_hideUser.on) {
if ([objects count] == 0) {
NSLog(#"%#",[error localizedDescription]);
} else {
matches = objects[0];
[newOwner setValue:#"userHidden" forKeyPath:#"isHidden"];
NSLog(#"%#",[matches valueForKeyPath:#"isHidden"]);
}
} else {
if([objects count] == 0) {
NSLog(#"%#",[error localizedDescription]);
} else {
matches = objects[0];
[newOwner setValue:#"userNotHidden" forKeyPath:#"isHidden"];
NSLog(#"%#",[matches valueForKeyPath:#"isHidden"]);
}
}
}
This should set the value of the Core Data String that I use to determine whether a person is hidden or not, which I use later in my code as a conditional for loading data. However when I test this feature it doesn't seem to update the persistent data store (Core Data) when the user has flipped the switch. I have looked around everywhere and I found a reference to there being a delay in updating Core Data here -> Why does IOS delay when saving core data via a UIManagedDocument, however it doesn't seem to provide the answer to my problem.
I want to be able flip the switch and save that value so that when the user swipes over to another view controller it is immediately aware that the user has gone into "hiding" or offline so it does not show certain information.
A NSManagedObjectContext is a scratchpad. Changes you make within the context exist only within the context unless or until you save them to the context's parent (either the persistent store itself or another context).
You're not saving them. I'd assume you're therefore not seeing the change elsewhere because you're using different contexts. Meanwhile the change eventually migrates because somebody else happens to save.
See -save: for details on saving.
(aside: the key-value coding [newOwner setValue:#"userHidden" forKeyPath:#"isHidden"]-style mechanism is both uglier and less efficient than using an editor-generated managed object subclass; hopefully it's just there while you're debugging?)
Related
I'm experimenting with Firebase's FDataSnapshot to pull in data and I would like it to write its data to my core data using MagicalRecord.
According to Firebases "best practice" blog I need to keep a reference to the "handle" so it can be cleaned up later on. Further, they mention to put the FDSnapshot code in viewWillAppear.
I am wanting a callback so that when its finished doing its thing to update core data.
But I'm really note sure how to do that; its doing two things and giving a return at the same time.
// In viewWillAppear:
__block NSManagedObjectContext *context = [NSManagedObjectContext MR_context];
self.handle = [self.ref observeEventType:FEventTypeValue withBlock:^(FDataSnapshot *snapshot) {
if (snapshot.value == [NSNull null])
{
NSLog(#"Cannot find any data");
}
else
{
NSArray *snapshotArray = [snapshot value];
// cleanup to prevent duplicates
[FCFighter MR_truncateAllInContext:context];
for (NSDictionary *dict in snapshotArray)
{
FCFighter *fighter = [FCFighter insertInManagedObjectContext:context];
fighter.name = dict[#"name"];
[context MR_saveToPersistentStoreWithCompletion:^(BOOL contextDidSave, NSError *error){
if (error)
{
NSLog(#"Error - %#", error.localizedDescription);
}
}];
}
}
}];
NSFetchRequest *fr = [[NSFetchRequest alloc] initWithEntityName:[FCFighter entityName]];
fr.sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES]];
self.fighterList = (NSArray *) [context executeFetchRequest:fr error:nil];
[self.tableView reloadData];
In the above code, the core data reading does not wait for the firebase to complete.
Thus, my query -- how would I best combine a completion handler so that when it is complete to update core data, and reload the tableview.
Many thanks
This is a common issue when working with Asynchronous data.
The bottom line is that all processing of data returned from an async call (in this case, the snapshot) needs to be done inside the block.
Anything done outside the block may happen before the data is returned.
So some sudo code
observeEvent withBlock { snapshot
//it is here where snapshot is valid. Process it.
NSLog(#"%#", snapshot.value)
}
Oh, and a side note. You really only need to track the handle reference when you are going to do something else with it later. Other than that, you can ignore the handles.
So this is perfectly valid:
[self.ref observeEventType:FEventTypeValue withBlock:^(FDataSnapshot *snapshot) {
//load your array of tableView data from snapshot
// and/or store it in CoreData
//reload your tableview
}
I am using Core Data to store some information for my app.
I have a .xcdatamodeld file containing 8 entities, and I extract them on different views.
In one of the viewControllers, I call three of them. Like this:
AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication]delegate];
managedObjectContext = appDelegate.managedObjectContext;
NSManagedObjectContext *moc = [self managedObjectContext];
NSEntityDescription *entiAll = [NSEntityDescription entityForName:#"AllWeapons" inManagedObjectContext:moc];
NSFetchRequest *frAll = [[NSFetchRequest alloc] init];
[frAll setEntity:entiAll];
NSError *error = nil;
arrAll = [moc executeFetchRequest:frAll error:&error];
displayArray = [[NSMutableArray alloc]initWithArray:arrAll];
NSEntityDescription *entiRange = [NSEntityDescription entityForName:#"WeaponsRanged" inManagedObjectContext:moc];
NSFetchRequest *frRanged = [[NSFetchRequest alloc] init];
[frRanged setEntity:entiRange];
NSError *errorRanged = nil;
arrRange = [moc executeFetchRequest:frRanged error:&errorRanged];
NSLog(#"%i, %i", [arrRange count], [[moc executeFetchRequest:frRanged error:&errorRanged] count]);
NSEntityDescription *entiMelee = [NSEntityDescription entityForName:#"WeaponsMelee" inManagedObjectContext:moc];
NSFetchRequest *frMelee = [[NSFetchRequest alloc] init];
[frMelee setEntity:entiMelee];
NSError *errorMelee = nil;
arrMelee = [moc executeFetchRequest:frMelee error:&errorMelee];
NSLog(#"%i, %i", [arrMelee count], [[moc executeFetchRequest:frMelee error:&errorMelee] count]);
The problem is that the middle one (the one filling the arrRange-array) doesn't work..
arrAll logs out with all correct data, arrMelee logs out with all the correct data (x4 for some reason, don't know if this is related :S), but arrRange logs out as an empty array.
[arrRange count]; gives me 0, even though I know there is lots of data there.
I ran this code on the simulator, and found the .sqlite file, opened it in Firefox's SQLite Manager, and saw the correct data, 40 rows.
I went into the appDelegate, where I fill the CoreData when necessary, and saw that the method which downloads the data in JSON-format successfully sends it to the sqlite aswell.
Here I fill the CoreData with data from the json:
[self deleteAllObjects:#"WeaponsRanged"];
NSManagedObjectContext *context = [self managedObjectContext];
for(NSDictionary *item in jsonWeaponRanged)
{
WeaponsRanged *wr = [NSEntityDescription insertNewObjectForEntityForName:#"WeaponsRanged"
inManagedObjectContext:context];
///***///
wr.recoil = [item objectForKey:#"Recoil"];
///***///
NSError *error;
if(![context save:&error])
NSLog(#"%#", [error localizedDescription]);
}
And if I here do NSLog(#"%# - %#", wr.recoil, [item objectForKey:#"Recoil"]); I get the correct data. (Same data on both)
So. The correct data is obviously in the core. But my NSFetchRequest or something is failing. I am pretty noob at Objective-C, so it might be my bad code-grammar striking again. I realize I should use things again etc, not creating new objects all the time.. But cmon, this is my first app.. And if that is actually the problem, I might learn. But I'm stuck.
SOMETIMES I get data, sometimes I don't. It's weird. I re-launched the app, and got data from it, and now I don't.. I haven't found a pattern yet..
Anyone?
Or is there another way to request data from the entity?
I have some suggestions, too big for a comment.
1) after you create the WeaponsRanged, try reading them back:
for(NSDictionary *item in jsonWeaponRanged)
{
WeaponsRanged *wr = [NSEntityDescription insertNewObjectForEntityForName:#"WeaponsRanged"
inManagedObjectContext:context];
NSLog(#"IS WR Realized? %#", wr ? #"YES" : #"NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO WR");
///***///
wr.recoil = [item objectForKey:#"Recoil"];
///***///
NSError *error;
if(![context save:&error])
NSLog(#"%#", [error localizedDescription]);
}
// Now lets see if we can retrieve them:
{
NSEntityDescription *entiRange = [NSEntityDescription entityForName:#"WeaponsRanged" inManagedObjectContext:context];
NSFetchRequest *frRanged = [[NSFetchRequest alloc] init];
[frRanged setEntity:entiRange];
NSError *errorRanged = nil;
arrRange = [context executeFetchRequest:frRanged error:&errorRanged];
NSLog(#"Wrote %i items, read back %i items", [jsonWeaponRanged count], [arrRange count] );
}
2) In the viewController reading WeaponsRanged, add an assert before the fetch on mod:
NSLog(#"IS moc set? %#", moc ? #"YES" : #"NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO MOC");
EDIT:
3) Spread statements everywhere you access the MOC:
assert([NSThread isMainThread]);
[If you haven't used asserts before google and read up on the topic. These are a powerful tool for developers to find out about potential problems way before they manifest themselves in the gui or elsewhere. They are normally compiled out for release/distribution builds.]
This will force an exception if the thread is not the main thread, and then let you track down the reason by following the stack trace.
Nevermind! It was my own damn fault (yet again..).
The problem occured before the code I presented, and it turns out the data was never in the .sqlite-file when the problem was present.
This is what I had:
I collected data from the internet through json-request. I have told the app to check the "version" of the data through the internet, and if the data is outdated, then re-download it.
First, I download all data, then I add them to their own entity in Core Data. After downloading, I clear the current Core Data entity of the downloaded data. So on the top of each add-method it said i.e [self deleteAllObjectsOfEntity:#"WeaponsRanged"];, My whole problem was that in the addMelee-method, it ALSO said [self deleteAllObjectsOfEntity:#"WeaponsRanged"]; instead of #"WeaponsMelee", thus deleting all ranged weapons, and later adding melee to the melee entity. And that also proves that the other problem I mentioned of arrMelee logging out four times as much data as it should was caused by this.
The reason it sometimes worked was that the downloading is not happening in any ordered mode. So the addRanged was sometimes called before the addMelee. If ranged comes first, it clears the arrRanged, and fills it up with correct data, and THEN melee comes, and clears it out. When melee was called first, it cleared arrRanged and filled additional data to arrMelee, and THEN ranged comes and tries to clear an empty entity, and then fills it up with correct data.
The solution was obviously to change the entity deleted when adding it, as it was the wrong one.
Sorry.... :)
Core Data Noob here.
I have a project, it saves data to a single entity no problemo. However, because the entity has way too many properties (over 100) it gets a warning that I need to normalize it. OK, so i create a second entity to store more data with To-One relationships both ways.
Problem is that when i try to save data, data saves and reloads to the first entity, but will not save or reload from the second. I must be missing something simple.
Here is some code:
//ViewDidLoad
- (void)viewDidLoad
{
if (managedObjectContext == nil) {
managedObjectContext = [(CoreDataStuffAppDelegate *) [[UIApplication sharedApplication] delegate] managedObjectContext];
NSLog(#"After managedObjectContext: %#", managedObjectContext);
}
// [self addRecord];
[super viewDidLoad];
if ([self fetchData]) {
NSLog(#"after self fetchData patientArray count is %i", [parentArray count]);
if ([parentArray count] == 1) {
Parent *parentInfo = (Parent *)[parentArray objectAtIndex:0];
parentItem1.text = parentInfo.Mother;
NSLog(#"fetching on load %i", [parentArray count]);
//Try 1: just going after the relationship route (FAIL: cuz data wont store. stays null)
// childItem1.text = parentInfo.ParentToChild.Kid;
// Try 2: going the route of directly talking to the second entity
childItem1.text = child.Kid;
}
}
// Save Record
- (void)saveRecord{
if (managedObjectContext == nil) {
NSLog(#"there is no context, arrg");
}
NSLog(#"array count is %i", [parentArray count]);
if ([parentArray count] == 1) {
NSManagedObjectContext *context = managedObjectContext;//[parent managedObjectContext];
NSLog(#"context 1 is: %#", context);
Parent *parentInfo = (Parent *)[parentArray objectAtIndex:0];
parentInfo.Mother = parentItem1.text;
NSLog(#"data says: %#", parentInfo.Mother);
NSLog(#"text syas: %#", parentItem1.text);
// Try 1, save it through the child relationship thing. (failed)
// parentInfo.ParentToChild.Kid = childItem1.text;
// NSLog(#"childSave says: D: %# T: %#", parentInfo.ParentToChild.Kid , childItem1.text);
// Try 2. from Resipeas app
if (!child) {
self.child = [NSEntityDescription insertNewObjectForEntityForName:#"Child" inManagedObjectContext:context];
[parent addChildObject:child];
NSLog(#"I hit the child");
}
child.Kid = childItem1.text;
NSLog(#"1: childSave says: D: %# T: %#", parentInfo.ParentToChild.Kid , childItem1.text);
NSLog(#"2: childSave says: D: %# T: %#", child.Kid , childItem1.text);
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"context 2 is: %#", context);
NSLog(#"major fail %#", [error localizedDescription]);
// abort();
}
}
NSLog(#"saving stuff");
}
// FetchData
- (BOOL)fetchData {
NSLog(#"doing the fetch");
BOOL returnResult = FALSE;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
if (managedObjectContext == nil)
{
NSLog(#"ok making a new managed object context");
managedObjectContext = [(CoreDataStuffAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Parent" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:1];
NSError *error;
NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:fetchRequest error:&error] mutableCopy];
if (mutableFetchResults == nil) {
NSLog(#"Fetching Error");
} else {
[self setParentArray:mutableFetchResults];
returnResult = TRUE;
NSLog(#"Fetching went well");
}
[mutableFetchResults release];
[fetchRequest release];
return (returnResult);
}
Okay, firstly, I think you have a conceptual problem here because I have never seen the need for an entity with 100 attributes. Most entities have a around a half-dozen attributes and I think the most I've ever seen was around 20.
Core Data is first and foremost an object graph management system with persistence tossed in as an option. It is intended to implement the model layer of a Model-View-Controller(MVC) design. As such, Core Data is primarily about modeling data not storing it.
Entities are intended to represent some real-world object, condition or event. There aren't a lot of real-world things that have a 100 attributes. E.g. You want to make a detailed model of a person. You want things like first name, last name, address(with attributes for each address component), driver's license# and date of issue, place of employment with address, social security number etc. If you tried to cram all that into one Person entity you could end up with a dozens of attributes. However, if you look closely at the data you are modeling and the relationships within the data, you would note that in the real world, addresses, driver's license, places of employment etc are not actually attributes of real people but rather other real-objects related to real people. Therefore, the best approach would be to break out the attributes for those objects into separate entities and create relationships to the Person entity. This makes model more realistic as well. After all, more than one person can live at the same address or work at the same place.
So, you probably need to start over from scratch and rethink your data model design.
Make sure you understand the difference between entities and managedObjects. Entities are abstract and serve merely to define keys, value types and relationships for managedObjects. Entities are to managedObjects as classes are to instances.
You have two other problems:
(1) You can only use the dot syntax accessor forms e.g parentInfo.ParentToChild.Kid if you have defined custom NSManagedObject subclasses for your entities. Otherwise, you are using generic NSManagedObject instances and must use the key-value methods e.g. [parent setvalue:forKey].
(2) A fetch returns only objects of one entity. So if you have a Parent entity and a Child entity. Each fetch returns instances of either Parent or Child but never both (unless they both inherit from the fetch's entity.)
i'm making a simple document-based application in Cocoa. Each document of this app should basically manage an array of Dates and Notes, so each record is a date and a note (textview). Also each document is protected by password.
To do that i created a Core Data entity called HistoryElement (that contains a date and a notes attribute), i also created a Settings entity that should have only a record which contains the password to open the file (i didn't found a better method, there is one ? The password is tied to each file, so i can't use preferences because it's not a global application password).
I have a preference tab which contain a Password textfield that binds to the password attribute of the Settings entity.
Ok...the problem is now this: when i create a new document there are no records on the Settings entity, so i wish to programmatically add one, so the user can put (if it want to protect it's file) the password in the password text field.
Instead, if i'm opening an existing file it should find that a record for Settings entity has been already add and it shouldn't create it again, instead the password text field should use this one.
I tried many ways, but i'm unable to do that. I tried for example this:
if([[settingsArrayController arrangedObjects] count] == 0) {`
NSLog(#"Init settings");`
[settingsArrayController add:self];`
}
It seems that it adds a new record when i create a new document, but if i put a password in the password text field and then save the document, when i open the document again the [[settingsArrayController arrangedObjects] count] returns 0 and it creates a new record again...
How can i do that ? There is a better/simple/elegant way to protect a document with a password ?
You need to add the code to NSPersistentDocument after the managedObjectContext has been initialized and the data has been loaded. It's hard to say what's wrong with the sample code you posted without knowing where you put it.
One easy place you could put it is in the windowControllerDidLoadNib. For example,
- (void)windowControllerDidLoadNib:(NSWindowController *)windowController
{
[super windowControllerDidLoadNib:windowController];
// user interface preparation code
NSManagedObjectContext *moc = [self managedObjectContext];
NSSet *settings = [moc fetchObjectsForEntityName:#"Settings"
withPredicate:nil];
if ([settings count] == 0)
{
NSManagedObject *obj = [NSEntityDescription insertNewObjectForEntityForName:#"Settings"
inManagedObjectContext:moc];
[obj setValue:#"myPass" forKey:#"password"];
} else {
// password record already exists, do something else.
}
}
Note that I am using a category on NSManagedObjectContext that does all the boiler plate query stuff:
// Convenience method to fetch the array of objects for a given Entity
// name in the context, optionally limiting by a predicate or by a predicate
// made from a format NSString and variable arguments.
//
- (NSSet *)fetchObjectsForEntityName:(NSString *)newEntityName
withPredicate:(id)stringOrPredicate, ...
{
NSEntityDescription *entity = [NSEntityDescription
entityForName:newEntityName inManagedObjectContext:self];
NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
[request setEntity:entity];
if (stringOrPredicate)
{
NSPredicate *predicate;
if ([stringOrPredicate isKindOfClass:[NSString class]])
{
va_list variadicArguments;
va_start(variadicArguments, stringOrPredicate);
predicate = [NSPredicate predicateWithFormat:stringOrPredicate
arguments:variadicArguments];
va_end(variadicArguments);
}
else
{
NSAssert2([stringOrPredicate isKindOfClass:[NSPredicate class]],
#"Second parameter passed to %s is of unexpected class %#",
sel_getName(_cmd), [stringOrPredicate className]);
predicate = (NSPredicate *)stringOrPredicate;
}
[request setPredicate:predicate];
}
NSError *error = nil;
NSArray *results = [self executeFetchRequest:request error:&error];
if (error != nil)
{
[NSException raise:NSGenericException format:#"%#",[error description]];
}
return [NSSet setWithArray:results];
}
And that should be all there is to it.
I have created a quick sample project that illustrates what you need to do at: http://dl.dropbox.com/u/21359504/coredata-example.zip
Is it possible to make a Core Data attribute unique, i.e. no two MyEntity objects can have the same myAttribute?
I know how to enforce this programatically, but I'm hoping there's a way to do it using the graphical Data Model editor in xcode.
I'm using the iPhone 3.1.2 SDK.
Every time i create on object I perform a class method that makes a new Entity only when another one does not exist.
+ (TZUser *)userWithUniqueUserId:(NSString *)uniqueUserId inManagedObjectContext:(NSManagedObjectContext *)context
{
TZUser *user = nil;
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:#"TZUser" inManagedObjectContext:context];
request.predicate = [NSPredicate predicateWithFormat:#"objectId = %#", uniqueUserId];
NSError *executeFetchError = nil;
user = [[context executeFetchRequest:request error:&executeFetchError] lastObject];
if (executeFetchError) {
NSLog(#"[%#, %#] error looking up user with id: %i with error: %#", NSStringFromClass([self class]), NSStringFromSelector(_cmd), [uniqueUserId intValue], [executeFetchError localizedDescription]);
} else if (!user) {
user = [NSEntityDescription insertNewObjectForEntityForName:#"TZUser"
inManagedObjectContext:context];
}
return user;
}
From IOS 9 there is a new way to handle unique constraints.
You define the unique attributes in the data model.
You need to set a managed context merge policy "Merge policy singleton objects that define standard ways to handle conflicts during a save operation" NSErrorMergePolicy is the default,This policy causes a save to fail if there are any merge conflicts.
- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
[_managedObjectContext setMergePolicy:NSOverwriteMergePolicy];
return _managedObjectContext;
}
The various option are discussed at Apple Ducumentation Merge Policy
It is answered nicely here
Zachary Orr's Answer
and he has kindly also created a blogpost and sample code.
Sample Code
Blog Post
The most challenging part is to get the data Model attributes editable.The Secret is to left click and then right click, after you have clicked the + sign to add a constraint.
I've decided to use the validate<key>:error: method to check if there is already a Managed Object with the specific value of <key>. An error is raised if this is the case.
For example:
- (BOOL)validateMyAttribute:(id *)value error:(NSError **)error {
// Return NO if there is already an object with a myAtribute of value
}
Thanks to Martin Cote for his input.
You could override the setMyAttribute method (using categories) and ensure uniqueness right there, although this may be expensive:
- (void)setMyAttribute:(id)value
{
NSArray *objects = [self fetchObjectsWithMyValueEqualTo:value];
if( [objects count] > 0 ) // ... throw some exception
[self setValue:value forKey:#"myAttribute"];
}
If you want to make sure that every MyEntity instance has a distinct myAttribute value, you can use the objectID of the NSManagedObject objects for that matter.
I really liked #DoozMen approach!!
I think it's the easiest way to do what i needed to do.
This is the way i fitted it into my project:
The following code cycles while drawing a quite long tableView, saving to DB an object for each table row, and setting various object attributes for each one, like UISwitch states and other things: if the object for the row with a certain tag is not present inside the DB, it creates it.
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:#"Obiettivo" inManagedObjectContext:self.managedObjectContext];
request.predicate = [NSPredicate predicateWithFormat:#"obiettivoID = %d", obTag];
NSError *executeFetchError = nil;
results = [[self.managedObjectContext executeFetchRequest:request error:&executeFetchError] lastObject];
if (executeFetchError) {
NSLog(#"[%#, %#] error looking up for tag: %i with error: %#", NSStringFromClass([self class]), NSStringFromSelector(_cmd), obTag, [executeFetchError localizedDescription]);
} else if (!results) {
if (obbCD == nil) {
NSEntityDescription *ent = [NSEntityDescription entityForName:#"Obiettivo" inManagedObjectContext:self.managedObjectContext];
obbCD = [[Obiettivo alloc] initWithEntity:ent insertIntoManagedObjectContext:self.managedObjectContext];
}
//set the property that has to be unique..
obbCD.obiettivoID = [NSNumber numberWithUnsignedInt:obTag];
[self.managedObjectContext insertObject:obbCD];
NSError *saveError = nil;
[self.managedObjectContext save:&saveError];
NSLog(#"added with ID: %#", obbCD.obiettivoID);
obbCD = nil;
}
results = nil;
Take a look at the Apple documentation for inter-property validation. It describes how you can validate a particular insert or update operation while being able to consult the entire database.
You just have to check for an existing one :/
I just see nothing that core data really offers that helps with this. The constraints feature, as well as being broken, doesn't really do the job. In all real-world circumstances you simply need to, of course, check if one is there already and if so use that one (say, as the relation field of another item, of course). I just can't see any other approach.
To save anyone typing...
// you've download 100 new guys from the endpoint, and unwrapped the json
for guy in guys {
// guy.id uniquely identifies
let g = guy.id
let r = NSFetchRequest<NSFetchRequestResult>(entityName: "CD_Guy")
r.predicate = NSPredicate(format: "id == %d", g)
var found: [CD_Guy] = []
do {
let f = try core.container.viewContext.fetch(r) as! [CD_Guy]
if f.count > 0 { continue } // that's it. it exists already
}
catch {
print("basic db error. example, you had = instead of == in the pred above")
continue
}
CD_Guy.make(from: guy) // just populate the CD_Guy
save here: core.saveContext()
}
or save here: core.saveContext()
core is just your singleton, whatever holding your context and other stuff.
Note that in the example you can saveContext either each time there's a new one added, or, all at once afterwards.
(I find tables/collections draw so fast, in conjunction with CD, it's really irrelevant.)
(Don't forget about .privateQueueConcurrencyType )
Do note that this example DOES NOT show that you, basically, create the entity and write on another context, and you must use .privateQueueConcurrencyType You can't use the same context as your tables/collections .. the .viewContext .
let pmoc = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
pmoc.parent = core.container.viewContext
do { try pmoc.save() } catch { fatalError("doh \(error)")}