awakeFromInsert called twice with nested contexts

问题

This project uses Mogenerator and Magical Record. I have tracked down a bug to the fact that awakeFromInsert is getting called twice. Once for each of my contexts I presume. This is an issue because I need to listen for NSNotifications on this NSManagedObject like this:

- (void)awakeFromInsert
{
    // Listen for a return from background mode
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(enteringForeground:) name:UIApplicationWillEnterForegroundNotification object:nil];
}

But awakeFromInsert get's called twice which is rather annoying. I want to call a method ONCE when my NSManagedObject is first created.

After searching this solution seems to make a lot of sense. However I can't see how I can add a category onto NSManagedObject when using Mogenerator and MagicalRecord. Without some complex overriding.

In MagicalRecord MR_createEntity calls

if ([self respondsToSelector:@selector(insertInManagedObjectContext:)]) 
    {
        id entity = [self performSelector:@selector(insertInManagedObjectContext:) withObject:context];
        return entity;
    }

Is there a neater solution to this issue?

回答1:

Ok well this feels very hacky but appears to work. I created the following class methods on my human readable NSManagedObject class:

+ (id)insertInManagedObjectContext:(NSManagedObjectContext*)moc_ {

    JWBoard *newobject = [super insertInManagedObjectContext:moc_];
    [JWBoard awakeFromCreate:newobject];
    return newobject;
}

+ (void)awakeFromCreate:(JWBoard *)board
{
    // do setup stuff & add observers
}

Open to much better solutions!

回答2:

Open to much better solutions!

I wish! Would have been easy enough for apple to not invoke awakeFromInsert, or to at least provide a flag that's true in the context of a "parentProcessSaveRequest." If you look at the call stack for the not-first calls to awakeFromInsert, the stack always contains parentProcessSaveRequest.

Here's some terrible code proving as much:

- (void) awakeFromInsert 
{
    [super awakeFromInsert];

    NSArray* stackArray = [NSThread callStackSymbols];
    for (NSString* method in stackArray)
    {
        if ([method rangeOfString:@"_parentProcessSaveRequest"].location != NSNotFound)
        {
            NSLog(@"Parent insert %@",self.objectID);
            return;
        }        
    }
    NSLog(@"First insert %@",self.objectID);
    // Initialize here

}

And the log output -- the objectId stays the same:

2014-05-19 20:53:52.964 myApp[1891:a01f] First insert 0x6000000326c0 <x-coredata:///MyEntity/t496E9B17-E170-4A7C-B7D4-7D8B92433E1C2>
2014-05-19 20:53:53.531 myApp[1891:303] Parent insert 0xdca8000eb <x-coredata://7274869F-4BF3-4B8A-9270-A64E54476AAD/MyEntity/p14122>
2014-05-19 20:53:53.537 myApp[1891:303] Parent insert 0xdca8000eb <x-coredata://7274869F-4BF3-4B8A-9270-A64E54476AAD/MyEntity/p14122>

Seems to work for saving to any of the nested contexts that I have, ugly as it is.

Unfortunately I cant figure any reasonable way to determine whether awakeFromInsert is being called in the context of a parentProcessSaveRequest. Come on, Apple! Give us a flag here.

回答3:

here is the simplest one: when parentContext is null, means when this context is saved you can do you custom logic, for example incrementing table number

- (void)awakeFromInsert
 {

     if (!self.managedObjectContext.parentContext) {
         //setting tableNumber

         [self willChangeValueForKey:@"number"];
         [self setPrimitiveNumber:tableNumber];
         [self didChangeValueForKey:@"number"];
    }

 }

来源：https://stackoverflow.com/questions/19893775/awakefrominsert-called-twice-with-nested-contexts

标签

objective-c

core-data

mogenerator

magicalrecord-2.1