I have 3 entities that I generated with MOGenerator, I'd like to be able to get one of them back from their objectID
I tried this :
- (void)aMethod: (SpecialEntity1ID *)entityID
{
//This is a method from MagicalRecord but it doesn't matter(I think...).
NSManagedObjectContext *context = [NSManagedObjectContext MR_contextWithParent:[NSManagedObjectContext MR_defaultContext]];
SpecialEntity1 *entity1 = [context objectRegisteredForID:entityID]
//But this returns an NSManagedObject so it doesn't work...
}
Could someone help me get this object back with its ID ?
Since I don't know how to do it with the ID I'm currently working around it by making a method with an NSStringas a paramater instead of SecialEntity1ID that defines one of the attribute of this object (and is unique) and fetching the object.
I think getting back with his ID is better so any idea ?
You want to use existingObjectWithID:error: method of your NSManagedObjectContext and typecast the return type if you are 100% sure what it will be. I'd keep it generic i.e. let it return an NSManagedObject and then test its class elsewhere if you want to determine whether it belongs to a particular class.
- (Object*)retrieveObjectWithID:(ObjectID*)theID
{
NSError *error = nil;
Object *theObject = (Object*)[[NSManagedObjectContext contextForCurrentThread] existingObjectWithID:theID error:&error];
if (error)
NSLog (#"Error retrieving object with ID %#: %#", theID, error);
return theObject;
}
Related
I have problems with memory in my class methods.
I have created a class method which will fetch records from core data and return a NSArray.
These are the problem i face:
sometimes the data is returned properly, it works fine.
sometimes it returns a CFArray
a.how to deal with with type of array??
b.what does this type of array mean??
sometimes the array becomes a invalid object when returned to the class which called the method
But in all the ways NSArray inside the method has data. Why does it react in different ways every time? Is there any way to manage this problem?
Code snippet used:
+(NSArray *)retrieveEvents
{
NSArray *arrData;
NSError *error;
NSFetchRequest *fetch = [APPDEL.managedObjectModel fetchRequestTemplateForName:#"fetchEvents"];
arrData = [NSArray arrayWithArray:[APPDEL.managedObjectContext executeFetchRequest:fetch error:&error]];
return arrData;
}
I have a coredata project that I'm trying to programmatically update a number.
I'm retrieving objects from CoreData and then storing it into an array.
Then, I'm looping through that array to see if the current user's IP is present in the database and trying to update the number of times accessed for that specific array.
The problem is, it's updating all the objects, not just the current object in the looped array.
First, I get the info from core data like so:
- (void)fetchRecords {
// Define our table/entity to use
NSEntityDescription *entity = [NSEntityDescription entityForName:#"IPAddr" inManagedObjectContext:managedObjectContext];
// Setup the fetch request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
// Define how we will sort the records
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"ipDate" ascending:NO];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
[request setSortDescriptors:sortDescriptors];
// Fetch the records and handle an error
NSError *error;
NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
if (!mutableFetchResults) {
// Handle the error.
// This is a serious error and should advise the user to restart the application
}
// Save our fetched data to an array
[self setIpArray: mutableFetchResults];
}
Now, I'm trying to find if the current User IP is present in the fetched results, and if it's present, update the number of times accessed:
// see if the ip is present and update if necessary
-(void)ipPresent {
NSString * theCurrentIP = [self getGlobalIPAddress];
for (IPAddr *allips in ipArray)
{
if ([allips.ipNum isEqualToString:theCurrentIP]) {
NSLog(#"The IP %# was found.", theCurrentIP);
// update the ip
NSError *error = nil;
NSNumber *ipToUpdate = allips.ipAccess;
NSNumber *addIpAccess = [[NSNumber alloc] initWithInt:1];
NSNumber *updateIpAddress = [NSNumber numberWithFloat:([ipToUpdate floatValue] + [addIpAccess floatValue])];
[self.ipArray setValue:updateIpAddress forKey:#"ipAccess"];
if ([self.managedObjectContext save:&error]) { // write to database
NSLog(#"The IP Was Updated from %# to %#", ipToUpdate, updateIpAddress);
} else if (![self.managedObjectContext save:&error]) {
NSLog(#"failed with error: %#", error);
}
break;
} else {
NSLog(#"The IP %# was NOT found.", theCurrentIP);
}
}
}
I'm pretty sure the issue is with this line:
[self.ipArray setValue:updateIpAddress forKey:#"ipAccess"];
Again, it's updating ALL the entities and not just the one in the current loop.
Indeed. You are using the wrong method. self.ipArray is a NSMutableArray.
The method
- (void)setValue:(id)value forKey:(NSString *)key
is used for Key-Value Coding (which is what makes it work for Core Data objects), but when applied to an array, it will invoke setValue:forKey: on each entry in the array.
Now, you can see that you could also call setValue:forKey on the one single array element allips since its property is obviously KVC compliant -- otherwise you would be having a different problem, not see the values being set.
Note, that you could also just assign the property...
allips.ipAccess = updateIpAddress;
EDIT
Sorry, probably should have read slower... You do understand that you don't have to use a mutable array, right? You are not actually changing the array, just the elements in the array. An immutable collection means that the collection contents can not change, but when you have a pointer to an object, as long as that object is not immutable, you can still mutate its properties.
Thus, if you had an immutable array of Foo objects, you could do this...
for (Foo *foo in myImmutableArray) {
Bar *bar = [self getSomeNewBar];
[foo setBar:bar];
// If Foo is KVC compliant, you can do this too...
[foo setValue:bar for Key:#"bar"];
}
If, however, you call setValue:forKey on the array, it will be invoked for each element of the array. Note, that setValue:forKey is actually declared in the immutable NSArray.
EDIT
That comment was hard to read.
The core data object is just another object. It looks like you have subclassed it, and provided it with properties for the attributes. Just replace
[self.ipArray setValue:updateIpAddress forKey:#"ipAccess"];
with
[allips setValue:updateIpAddress forKey:#"ipAccess"];
or
allips.ipAccess = updateIpAddress;
Either of those should modify your core data object, as they would any object that had a read/write property named "ipAccess"
Assuming, of course, that I didn't read it wrong again... and allips is your core data object...
I have CoreData in my app, with an Entry class, which contains an NSOrderedSet of Media classes.
I then have this code, for adding a new Media item to the NSOrderedSet:
-(void)addImage:(UIImage *)image isInPhotoLibrary:(BOOL)isInPhotoLibrary {
Media *media = [[Media alloc] init];
media.type = #"Image";
media.originalImage = UIImageJPEGRepresentation(image, 1.0);
media.isInPhotoLibrary = [NSNumber numberWithBool:isInPhotoLibrary];
[self addMediaObject:media];
}
Will this automatically save the changes, or will I have to do it myself. If so, will i then need to pass in a context to do this, or is there another way?
No, this code doesn't have any Core Data references at all.
Is Media an NSManagedObject? If so you need to be creating it like so:
Media *media = [NSEntityDescription insertNewObjectForEntityForName:#"Media" inManagedObjectContext:context];
This will put it in your managed object context.
If you then want to persist it, you will need to call save: on the managed object context.
EDIT ALSO....
In your Entry class, you will probably have a generated method that you use to add objects to the NSSet. It will be in a category (CoreDataGeneratedAccessors) on the Entry header file
- (void)addMediaObject:(Media *)value;
No it won't.. If you want to save changes to Database in Core data you gotta call save function for that.. I assume Media is kind of NSManagedObject class. To save the changes to persistent store you have to call save method . Until then the changes are just temporary present on your scratch board/ ManagedObjectContext.
This is how I save changes:
Worker *worker = (Worker *)[NSEntityDescription insertNewObjectForEntityForName:#"Worker" inManagedObjectContext:self.managedObjectContext];
worker.name=txtContact.text;
worker.address=txtAddress.text;
worker.zipCode=txtZip.text;
worker.city=txtCity.text;
worker.mobile=txtMobile.text;
NSError *error;
if (![managedObjectContext save:&error])
{
NSLog(#"Whoops, couldn't save: %#", [error localizedDescription]);
}
I have an app that uses Core Data and it gets its ManagedObjectContext by using UIManagedObject. From reading, I see that I am not suppose to save the context directly - rather I should depend on autosaving of UIManagedObject or use saveToURL:... My issue is that I want to validate the data being stored in my entity. I have constraints on the entity that specify that the min length for the string properties is 1. However, I can create a new object, assign its properties empty strings, and save the file. In the completion handler of saveToURL:... it always has a true success value. I then created my own validator for the name property of my entity. I used sample code from the Core Data Programming Guide -
-(BOOL)validateName:(id *)ioValue error:(__autoreleasing NSError **)outError
{
if (*ioValue == nil)
{
if (outError != NULL)
{
NSString *errorStr = #"nil error";
NSDictionary *userInfoDict = [NSDictionary dictionaryWithObject:errorStr
forKey:NSLocalizedDescriptionKey];
NSError __autoreleasing *error = [[NSError alloc] initWithDomain:#"domain"
code:1
userInfo:userInfoDict];
*outError = error;
}
return NO;
}
else if( [*ioValue length] == 0 )
{
if (outError != NULL) {
NSString *errorStr = #"length error";
NSDictionary *userInfoDict = [NSDictionary dictionaryWithObject:errorStr
forKey:NSLocalizedDescriptionKey];
NSError __autoreleasing *error = [[NSError alloc] initWithDomain:#"domain"
code:1
userInfo:userInfoDict];
*outError = error;
}
return NO;
}
else
{
return YES;
}
}
When this runs, I see that the ioValue has 0 length and that it returns NO, but then my completion handler is never called. Any help would be great.
Is there something I am missing for how to handle saving errors with UIManagedDocument - particularly how to notify the calling code that an error happened while saving its information.
As a rule, you should only call saveToURL to create a brand new file. Let auto-save do the rest.
Also, I'm not sure I follow your question. If you are asking how to know about save failures, the best you can do is register for notifications (since all saves happen on a background thread).
Directly from the documentation:
A UIDocument object has a specific state at any moment in its life cycle. You can check the current state by querying the documentState property. And you can be notified of changes in the state of a document by observing the UIDocumentStateChangedNotification notification.
I guess I need to implement handleError:(NSError *)error userInteractionPermitted:(BOOL)userInteractionPermitted in a subclass of the UIManagedDocument. I found that via this article - http://blog.stevex.net/2011/12/uimanageddocument-autosave-troubleshooting/
So im really new to core data, but i went through a tutorial and pretty much understand it, well at least the idea behind most of the things. But I still have 1 question that i cant find anywhere. It seems really simple but here it is. If I were to have two strings inside one entity lets say:
1.name
2.position
If the name is already entered how might i allow a user to enter text into a textField and assign it to their position at a later time? Even if there were 20 names, considering no duplicates?
I was thinking it might be something like this...But it doesnt seem to work.
UserInfo *userInfo = (UserNumber *)[NSEntityDescription insertNewObjectForEntityForName:#"UserInfo" inManagedObjectContext:managedObjectContext];
if ([userName isEqualToString:"#James"]) {
userInfo.Position = nameField.text;
}
On the code above you are casting (UserNumber*) to an object that you are declaring as (UserInfo*)? Which is what and is there any reason why you are doing that?
If I understand your question correctly, you want to create a record with only the username pre-populated and then allow that record to be updated at a later stage.
I will assume your entity is called UserInfo and that there are 2 NSString properties created for it - userName and position. I also assume you have created the class files for UserInfo and imported the header into the relevant view controllers.
Here's how you would do it:
1) Firstly, assuming you have username typed in a UITextField *userNameField, let's create a new record.
UserInfo *userInfo = (UserInfo*)[NSEntityDescription insertNewObjectForEntityForName:#"UserInfo" inManagedObjectContext:self.managedObjectContext];
[userInfo setValue:userNameField.text forKey:#"userName"];
This will create a new instance of UserInfo in your managed object context and set the value of userName to the value on userNameField.text
Then at a later stage a user will get to a point where they can update their records in your app (you may need to think about authentication somewhere here). You will fetch the record that matches your specified username:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSPredicate *userNamePredicate = [NSPredicate predicateWithFormat:#"(userName == %#)", userNameField.text];
[fetchRequest setPredicate:userNamePredicate];
NSEntityDescription *userInfo = [NSEntityDescription entityForName:#"UserInfo" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:userInfo];
NSError *error;
NSArray *fetchRequestArray = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
[fetchRequest release];
If the fetchRequest found match(es) to your userNameField.text paramater, they will be saved in the fetchRequestArray. There should only be a maximum of one object there if you take the necessary steps to make the userName property mandatory AND unique.
Access the object by grabbing the objectAtIndex:0 in the array and change it's position property:
UserInfo *userInfoToBeEdited = [fetchRequestArray objectAtIndex:0];
[userInfoToBeEdit setValue:positionTextField.text forKey:#"position"];
In both cases above, remember to invoke CoreData's save method when you are ready to commit your changes. Before save is invoked your changes are only kept in your managed object context which is basically a scratch pad for your persistent data.
[EDIT TO ADD SAVE METHOD]
As per your comment, I usually have the save method below in my AppDelegate (copy/paste directly from Apple template)
- (void)saveContext
{
error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil)
{
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])
{
[self seriousErrorAlert];
}
}
}
And then whenever I need to save changes, from any view controller I simply grab a reference to my AppDelegate and fire it off:
AppDelegate *theDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
[theDelegate saveContext];