Core Data with NSXMLParser on iPhone saving object incorrectly

Question

Hey Folks,

I'm new to Objective-C, XCode and iPhone development in general and I'm having some issues with Core Data and NSXMLParser.

Having followed Apples' tutorials SeismicXML (for NSXMLParser) and the Core Data on iPhone tutorial I've ran into an issue when assigning values to my Managed Object Models' entities properties.

To explain the situation my code only varies from the SeismicXML example by using CoreData to assign the currentParsedCharacterData to my managed objects rather than the standard NSObject which the SeismicXML project uses.

Below is the description output from my managed object.

county = "-53.25354768,4.256547";
friendly = "-53.25354768,4.256547";
image = nil;
latitude = -53.253547684;
link = "-53.25354768,4.256547";
longitude = nil;
name = "-53.25354768,4.256547";
postcode = "-53.25354768,4.256547";
shopDescription = nil;
shopID = 0;
tag = "-53.25354768,4.256547";
tags =     (
);
telephone = "-53.25354768,4.256547";
town = "-53.25354768,4.256547";

What appears to be happening is that all of the attributes/properties are assigned the value of the last node in my XML feed; which happens to be longitude, latitude. Yet when logging parsed character data at the time of the property assignment it is the expected (and correct) value but when outputting the description of this object all string values are wrong and number values/otherwise are simply 0 or nil.

Any suggestions would be extremely appreciated. If need be I can knock up a smaller project which shows this behaviour with the same XML feed that I am using.

EDIT:

Here is an abbreviated example of what I am doing to get information into the managed object which results in the same error.

For convenience sake I have a zip of the project http://willb.ro/CoreDataProblemExample.zip

Debug Output 2009-11-16 14:31:20.357 ShittyExample[4360:4d07] Company Description: (entity: Company; id: 0x3f6e9e0 ; data: { companyDescription = "Top Shop are a leading brandname in the retail sec"; companyID = 66136112; name = "Top Shop are a leading brandname in the retail sec"; })

//XML
<channel>
    <company id="1">
     <name>Top Shop</name>
     <description>Top Shop are a leading brandname in the retail sector.</description>
    </company>
</channel>

// FeedImporter.h

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@class RootViewController, Company;

@interface FeedImporter : NSObject {
    NSManagedObjectContext *managedObjectContext;
    RootViewController *rootViewController;
    NSMutableArray *companyList;

    // for downloading the xml data
    NSURLConnection *companyFeedConnection;
    NSMutableData *companyData;

    // these variables are used during parsing
    Company *currentCompanyObject;
    NSMutableArray *currentParseBatch;
    NSUInteger parsedCompaniesCounter;
    NSMutableString *currentParsedCharacterData;
    BOOL accumulatingParsedCharacterData;
    BOOL didAbortParsing;
}

@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;

@property (nonatomic, retain) RootViewController *rootViewController;
@property (nonatomic, retain) NSMutableArray *companyList;

@property (nonatomic, retain) NSURLConnection *companyFeedConnection;
@property (nonatomic, retain) NSMutableData *companyData;

@property (nonatomic, retain) Company *currentCompanyObject;
@property (nonatomic, retain) NSMutableString *currentParsedCharacterData;
@property (nonatomic, retain) NSMutableArray *currentParseBatch;

- (void)parseFeed;
- (void)addCompaniesToList:(NSArray *)companies;
- (void)handleError:(NSError *)error;

@end

// FeedImporter.m    

#import "FeedImporter.h"
#import "RootViewController.h"
#import <CFNetwork/CFNetwork.h>
#import "Company.h"

@implementation FeedImporter

@synthesize managedObjectContext;
@synthesize rootViewController;

@synthesize companyList;
@synthesize companyFeedConnection;
@synthesize companyData;

@synthesize currentCompanyObject;
@synthesize currentParseBatch;
@synthesize currentParsedCharacterData;


- (void)dealloc {
    [super dealloc];
    [managedObjectContext release];
    [rootViewController release];
    [companyList release];
    [companyFeedConnection release];
    [companyData release];

    [currentCompanyObject release];
    [currentParseBatch release];
    [currentParsedCharacterData release];
}

- (id)init {
    if(self = [super init]) {
     // Custom loading logic goes here..
    }
    return self;
}

- (void)parseFeed {
    static NSString *feedURLString = @"http://willb.ro/companies.xml";
    NSURLRequest *companyURLRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:feedURLString]];

    self.companyFeedConnection = [[[NSURLConnection alloc] initWithRequest:companyURLRequest delegate:self] autorelease];

    NSAssert(self.companyFeedConnection != nil, @"Failure to create URL connection.");

    // Start the status bar network activity indicator. We'll turn it off when the connection finishes or experiences an error.
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
}

#pragma mark NSURLConnection delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    self.companyData = [NSMutableData data];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [companyData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;   
    if ([error code] == kCFURLErrorNotConnectedToInternet) {
        // if we can identify the error, we can present a more precise message to the user.
        NSDictionary *userInfo = [NSDictionary dictionaryWithObject:NSLocalizedString(@"No Connection Error",                             @"Error message displayed when not connected to the Internet.") forKey:NSLocalizedDescriptionKey];
        NSError *noConnectionError = [NSError errorWithDomain:NSCocoaErrorDomain code:kCFURLErrorNotConnectedToInternet userInfo:userInfo];
        [self handleError:noConnectionError];
    } else {
        // otherwise handle the error generically
        [self handleError:error];
    }
    self.companyFeedConnection = nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    self.companyFeedConnection = nil;
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;   

    [NSThread detachNewThreadSelector:@selector(parseCompanyData:) toTarget:self withObject:companyData];

    self.companyData = nil;
}

- (void)parseCompanyData:(NSData *)data {
    // You must create a autorelease pool for all secondary threads.
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    self.currentParseBatch = [NSMutableArray array];
    self.currentParsedCharacterData = [NSMutableString string];

    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
    [parser setDelegate:self];
    [parser parse];

    if ([self.currentParseBatch count] > 0) {
        [self performSelectorOnMainThread:@selector(addCompaniesToList:) withObject:self.currentParseBatch waitUntilDone:NO];
    }
    self.currentParseBatch = nil;
    self.currentCompanyObject = nil;
    self.currentParsedCharacterData = nil;

    // Save to our MOC...

    NSError *saveError;
    if(![self.managedObjectContext save:&saveError]) {
     // Handle MOM save error
     NSLog(@"error while saving shop to managed object model");

     NSError* error;
        if(![[self managedObjectContext] save:&error]) {
      NSLog(@"Failed to save to data store: %@", [error localizedDescription]);
      NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey];
      if(detailedErrors != nil && [detailedErrors count] > 0) {
       for(NSError* detailedError in detailedErrors) {
        NSLog(@"  DetailedError: %@", [detailedError userInfo]);
       }
      }
      else {
       NSLog(@"  %@", [error userInfo]);
      }
        }

    }
    else
    {
     NSLog(@"MOC saved sucessfully");

    }

    [parser release];        
    [pool release];
}

#pragma mark Parser constants

// Limit the number of parsed companies to 50.
static const const NSUInteger kMaximumNumberOfCompaniesToParse = 50;

static NSUInteger const kSizeOfCompanyBatch = 10;

static NSString * const kChannelElementName = @"channel";
static NSString * const kCompanyElementName = @"company";
static NSString * const kCompanyNameElementName = @"name";
static NSString * const kCompanyDescriptionElementName = @"description";

- (void)addCompaniesToList:(NSArray *)companies {
    [self.companyList addObjectsFromArray:companies];
    // The table needs to be reloaded to reflect the new content of the list.
    [rootViewController.tableView reloadData];
}

#pragma mark NSXMLParser delegate methods

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict {
    if (parsedCompaniesCounter >= kMaximumNumberOfCompaniesToParse) {
        didAbortParsing = YES;
        [parser abortParsing];
    }
    if ([elementName isEqualToString:kCompanyElementName]) {
     Company *company = (Company *)[NSEntityDescription insertNewObjectForEntityForName:@"Company" inManagedObjectContext:self.managedObjectContext];
        self.currentCompanyObject = company;
        [company release];
     int companyIDInt = (int)[attributeDict valueForKey:@"id"];
     NSNumber *companyID = [NSNumber numberWithInt:companyIDInt];
     [self.currentCompanyObject setCompanyID:companyID];
    }
    else if ([elementName isEqualToString:kCompanyElementName] || [elementName isEqualToString:kCompanyNameElementName] || [elementName isEqualToString:kCompanyDescriptionElementName]) {
        accumulatingParsedCharacterData = YES;
        [currentParsedCharacterData setString:@""];
    }
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {     
    if ([elementName isEqualToString:kCompanyElementName]) {
     //NSLog(@"currentEarthquakeObject: %@", currentEarthquakeObject);
        [self.currentParseBatch addObject:self.currentCompanyObject];
        parsedCompaniesCounter++;
        if (parsedCompaniesCounter % kSizeOfCompanyBatch == 0) {
            [self performSelectorOnMainThread:@selector(addCompaniesToList:) withObject:self.currentParseBatch waitUntilDone:NO];
            self.currentParseBatch = [NSMutableArray array];
        }
     //NSLog(@"Reached end of company. Follows is a description of our company object: %@", [self.currentCompanyObject description]);
     NSLog(@"Company Description: %@", [self.currentCompanyObject description]);
    }
    else if ([elementName isEqualToString:kCompanyNameElementName]) {
     // Company Name
     [self.currentCompanyObject setName:self.currentParsedCharacterData];
     //NSLog(@"%@",self.currentParsedCharacterData);
    }
    else if ([elementName isEqualToString:kCompanyDescriptionElementName]) {
     // Company Description
     [self.currentCompanyObject setCompanyDescription:self.currentParsedCharacterData];
     //NSLog(@"%@",self.currentParsedCharacterData);
    }
    accumulatingParsedCharacterData = NO;
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    if (accumulatingParsedCharacterData) {
        [self.currentParsedCharacterData appendString:string];
    }
}


- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
    if (didAbortParsing == NO) {
        [self performSelectorOnMainThread:@selector(handleError:) withObject:parseError waitUntilDone:NO];
    }
}

- (void)handleError:(NSError *)error {
    NSString *errorMessage = [error localizedDescription];
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"Error Title", @"Title for alert displayed when download or parse error occurs.") message:errorMessage delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alertView show];
    [alertView release];
}

@end

Answer 1

It seems you are assigning where you ought to be copying. I'd have to see more of your code to be sure, but I'm almost certain a copy somewhere would solve your issues.

Answer 2

As stated above, i had the exact same problem. But would now recommend to bypass the useless NSXMLParser (if using it WITH core data!!!) and using GDataXML instead. GDataXML is modelled on the NSXMLDocument class (which is a more elegant and workable solution to use with core data, only that you can't use NSXMLDocument with iOS).

See here for an excellent tutorial: http://www.raywenderlich.com/725/how-to-read-and-write-xml-documents-with-gdataxml :)