Auto-generated code for inverse 1-to-many relation

问题:

I've created two entities in core data model (Courier and Occupation in this example), and created an inverse relationship between them, which also caused a crush in xcode. After that, I've set the relationship as one courier to many occupations and created classes.

The occupation class was created empty, but courier class was populated with following code:

- (void)addOccupationsObject:(NSManagedObject *)value {    
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"occupations" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"occupations"] addObject:value];
    [self didChangeValueForKey:@"occupations" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)removeOccupationsObject:(NSManagedObject *)value {
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"occupations" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"occupations"] removeObject:value];
    [self didChangeValueForKey:@"occupations" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)addOccupations:(NSSet *)value {    
    [self willChangeValueForKey:@"occupations" withSetMutation:NSKeyValueUnionSetMutation usingObjects:value];
    [[self primitiveValueForKey:@"occupations"] unionSet:value];
    [self didChangeValueForKey:@"occupations" withSetMutation:NSKeyValueUnionSetMutation usingObjects:value];
}

- (void)removeOccupations:(NSSet *)value {
    [self willChangeValueForKey:@"occupations" withSetMutation:NSKeyValueMinusSetMutation usingObjects:value];
    [[self primitiveValueForKey:@"occupations"] minusSet:value];
    [self didChangeValueForKey:@"occupations" withSetMutation:NSKeyValueMinusSetMutation usingObjects:value];
}

I have two questions about it:

1. What exactly does it do?
2. Does it guarantee consistency of this model? (I know it should, but after the crash I'm not sure if xcode's logic in generating this code was correct).
3. Why was occupation class created empty?

回答1:

1. What exactly does it do? If I understood this question, the methods created are the only way to add Occupations to courier. Because you cannot for example create a standard NSSet, add occupations to it and then add NSSet to Courier, you will get an error.

2. Does it guarantee consistency of this model? (I know it should, but after the crash I'm not sure if xcode's logic in generating this code was correct). Every change you made to the context is not saved until you explicitly call the relevant method, so yes, should be consistent. Beware that if you change the xcdatamodel, you will have to update or delete the sqllite file created before.

3. Why was occupation class created empty? If it is really empty there's something wrong. But probably it is not empty, it should have at least the attributes, then an attribute of type Courier which is your inverse relationship. In the implementation Occupation.m you should find lot of @dynamic , which tell the compilers to pass by because at run time a correct implementation will be provided.