XML to Core Data

When an XML schema and Core Data schema are mirrored: Parses an XML file, creates NSManagedObjects, and adds them to your Core Data store.

All in the background so it minimally affects your UI.

A visual explanation of the XML Schema.

<?xml version= "1.0" encoding="UTF8"?>
<root>
	<ParentEntity>
		<attribute>attribute data</attribute>
		<anotherAttribute>attribute data</anotherAttribute>
        // add an arbitrary number of attributes
		<relationshipToChildEntities>
			<ChildEntity>
				<childAttribute>child attribute data</childAttribute>
                    <relationshipToGranchildEntities>
                        <GrandchildEntity>
                            <grandchildAttribute>grandchild attribute data</grandchildAttribute>
                                <relationshipToGreatGranchildEntities>
                                    // go as deep as you'd like
                                </relationshipToGreatGranchildEntities>
                        </GrandchildEntity>
                        // add an arbitrary number of <GrandchildEntity>'s
                    </relationshipToGranchildEntities>
			</ChildEntity>
            <ChildEntity>
                // add an arbitrary number of <ChildEntity>'s
            </ChildObject>
        </relationshipToChildEntities>
    </ParentEntity>
    // add an arbitrary number of <ParentEntity>'s
</root>

View the "Schema_Illustration.pdf" for another visual example.

Features

• Parses XML data and saves Core Data objects in the background, thus minimally affecting the UI.
• Can handle large XML files (uses SAX instead of DOM).
• Can handle an arbitrary number of objects and 1-to-many relationships as long as the schemas match.
• Will traverse your object graph an arbitrary number of levels deep. (i.e. Parent objects with relationships of child objects with relationships of grandchild objects, etc.)
• Should work on both OSX and iOS.

How to Use

Add the DNXMLParseOperation header and implementation files to your project. (You can find them in the sample app.)

1. To start parsing:

NSData *xmlData = // load the xml file via a method of your choice

DNXMLParseOperation *parser = [[DNXMLParseOperation alloc] initWithData:xmlData];
parser.batchSize = 5;  // optional, defaults to 10

// Let an observer know to save and merge the managed object context
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(mergeChanges:)
                                             name:NSManagedObjectContextDidSaveNotification
                                           object:nil];

// Let an observer know if a parse error ocurred (optional, but recommended)                                        
[[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(handleParseError:) 
                                             name:kParseOperationErrorNotif 
                                           object:nil];
                                           
NSOperationQue *parseQue = [[NSOperationQueue alloc] init];
[parseQue addOperation:parser];

2. To cancel/abort parsing:

[parser cancel];

3. IMPORTANT, to save parsed objects to your Core Data store:

// Invoked by observing "NSManagedObjectContextDidSaveNotification" from our Parse Operation
- (void)mergeChanges:(NSNotification *)notification {
    NSManagedObjectContext *mainContext = [self managedObjectContext];
    if ([notification object] == mainContext) {
        // main context save, no need to perform the merge
        return;
    }
    [self performSelectorOnMainThread:@selector(updateContext:) withObject:notification waitUntilDone:YES];
}

// Invoked from mergeChanges: method,
// Must be on the main thread so we can update our table with our new objects
//
- (void)updateContext:(NSNotification *)notification
{
    NSManagedObjectContext *mainContext = [self managedObjectContext];
    [mainContext mergeChangesFromContextDidSaveNotification:notification];
    [self reloadTableView];
}

// Optional, but especially if using a table view, you must update the UI somehow
- (void)reloadTableView {
    // Force the fetchedResultsController to reload, then force the table view to reload.
    self.fetchedResultsController = nil;
    [self fetchedResultsController];
    [self.tableView reloadData];
}

4. Optional (but recommended), implement a method to handle notification kParseOperationErrorNotif

-(void)handleParseError:(NSNotification *)notification {
    NSError *parseError = [[notification userInfo] objectForKey:kParseOperationMsgErrorKey];
    NSString *errorMsg = [NSString stringWithFormat:@"Malformed data present. Unable to import new data. (Error Code: %i)", [parseError code]];
    // do something with the errorMsg such as show a UIAlertView
}

Limitations

• It does not sync or delete any objects. Only adds them. You will need to add this functionality.
• Assumes the XML file is downloaded locally.
• Currently, only works with 1-to-many relationships.
• Use camel case for XML tags. They must match the exact names of your Core Data entities, relationships, and attributes.

To Do

• Make debug NSLogs in parse operation more useful ex: "[NSManagedObject addValue:value forKey:key]""
• Test when NSManagedObjects are subclassed.
• Test 1-to-1 relationships.