CoreData: Same predicate (IN) returns different fe

Question

HUGE UPDATE：

I create a totally new project to mimic the problem, it does appear all the time!

Here is my data model:

Task has a to-many relationship pointing to Person.

@interface Person : NSManagedObject

@property (nonatomic, retain) NSString * personId;
@property (nonatomic, retain) NSString * name;

@end

//

@class Person;

@interface Task : NSManagedObject

@property (nonatomic, retain) NSNumber * taskId;
@property (nonatomic, retain) NSSet *watchers;
@end

@interface Task (CoreDataGeneratedAccessors)

- (void)addWatchersObject:(Person *)value;
- (void)removeWatchersObject:(Person *)value;
- (void)addWatchers:(NSSet *)values;
- (void)removeWatchers:(NSSet *)values;

@end

Now, I create two persons, p1 & p2, and two tasks, 1001 & 1002:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    Person *p1 = [self insertOrUpdatePerson:@"111" withName:@"aaa"];
    Person *p2 = [self insertOrUpdatePerson:@"222" withName:@"bbb"];

    [self insertOrUpdateTask:1001 withWatcher:p1];
    [self insertOrUpdateTask:1001 withWatcher:p2];

    [self insertOrUpdateTask:1002 withWatcher:p1];
    [self insertOrUpdateTask:1002 withWatcher:p2];

    NSArray *watchedTasks = nil;

    watchedTasks = [self fetchTasksWatchedByPerson:p1]; // return 2 objects
    NSLog(@"watchedTasks : %@\n", watchedTasks);
    [self saveContext];
    watchedTasks = [self fetchTasksWatchedByPerson:p1]; // return 1 objects
    NSLog(@"watchedTasks : %@\n", watchedTasks);

    NSArray *allTasks = [self fetchAllTasks]; // return 2 objects
    NSLog(@"allTasks : %@\n", watchedTasks);
}

And the log follows. Notice that the second output of watchedTasks has only one object!

Printing description of watchedTasks:
<__NSArrayI 0x8d5aff0>(
<Task: 0x8d5b240> (entity: Task; id: 0x8d5b3e0 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p2> ; data: {
    taskId = 1002;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
}),
<Task: 0x8d59d10> (entity: Task; id: 0x8d59420 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p1> ; data: {
    taskId = 1001;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
})
)

Printing description of updateObjects:
<__NSArrayI 0x8e41880>(
<Task: 0x8d59d10> (entity: Task; id: 0x8d59420 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p1> ; data: {
    taskId = 1001;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
}),
<Task: 0x8d5b240> (entity: Task; id: 0x8d5b3e0 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p2> ; data: {
    taskId = 1002;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
}),
<Person: 0x8d56cc0> (entity: Person; id: 0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1> ; data: {
    name = aaa;
    personId = 111;
}),
<Person: 0x8d57be0> (entity: Person; id: 0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2> ; data: {
    name = bbb;
    personId = 222;
})
)

Printing description of watchedTasks:
<_PFArray 0x8f57da0>(
<Task: 0x8d5b240> (entity: Task; id: 0x8d5b3e0 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p2> ; data: {
    taskId = 1002;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
})
)

Printing description of allTasks:
<_PFArray 0x8e44b30>(
<Task: 0x8d59d10> (entity: Task; id: 0x8d59420 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p1> ; data: {
    taskId = 1001;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
}),
<Task: 0x8d5b240> (entity: Task; id: 0x8d5b3e0 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Task/p2> ; data: {
    taskId = 1002;
    watchers =     (
        "0x8d57f80 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p2>",
        "0x8d56070 <x-coredata://706EB8CA-ACE7-48DB-89E1-7CCFCDD41DA4/Person/p1>"
    );
})
)
(lldb) 

So I open the .sqlite file to see what exactly in.

What surprise me first is that watchers is in the Person table, not in a middle/mapping Task2Person table. I remember that once the relationship exists in a middle table.

Then, the watchers field in the Person table contains only one value, not a set or array!

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    NSArray *watchedTasks = nil;

    Person *p1 = [self insertOrUpdatePerson:@"111" withName:@"aaa"];
    Person *p2 = [self insertOrUpdatePerson:@"222" withName:@"bbb"];

    watchedTasks = [self fetchTasksWatchedByPerson:p1]; // return 1 object

    Task *t1 = [self insertOrUpdateTask:1001 withWatcher:p1]; // update watchers in the memory
    [self insertOrUpdateTask:1001 withWatcher:p2];

    Task *t2 = [self insertOrUpdateTask:1002 withWatcher:p1];
    [self insertOrUpdateTask:1002 withWatcher:p2];

    watchedTasks = [self fetchTasksWatchedByPerson:p1]; // return 2 objects

    [self saveContext];

    watchedTasks = [self fetchTasksWatchedByPerson:p1]; // return 1 object

So I found that after I launch the App and read the tasks from the db file, only 1 object is returned.

When I update the watchers information for the tasks, 2 objects can be fetched.

Finally after I save the context, only 1 object again.

---

Just Ignore This

- Old Information Below

I have code below:

        NSArray *existedTasks = [[TaskBizDB sharedInstance] fetchTasksWatchedByMeOfProject:projectId];
        [context save:&error];
        existedTasks = [[TaskBizDB sharedInstance] fetchTasksWatchedByMeOfProject:projectId];

        NSArray *allTasks = [[TaskBizDB sharedInstance] fetchTasksOfProject:projectId];

• First line returns two objects;
• Second line save the context;
• Third line returns just one object, which is contained in the 'two objects' above;
• And the last line returns 6 objects, containing the 'two objects' returned at the first line.

The fetch interface works like below:

WXModel *model = [WXModel modelWithEntity:NSStringFromClass([WQPKTeamTask class])];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(%@ IN personWatchers) AND (projectId == %d)", currentLoginUser, projectId];
[model setPredicate:predicate];
NSArray *fetchedTasks = [model fetch];
if (fetchedTasks.count == 0) return nil;

return fetchedTasks;

What confused me is that, with the same fetch request, why return different results just after a save?

Here comes more detail:

The 'two objects' returned at the first line are:

<WQPKTeamTask: 0x1b92fcc0> (entity: WQPKTeamTask; id: 0x1b9300f0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p9> ; data: {
    projectId = 372004;
    taskId = 338001;
    personWatchers =     (
        "0xf0bf440 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WWPerson/p1>"
    );
}

<WQPKTeamTask: 0xf3f6130> (entity: WQPKTeamTask; id: 0xf3cb8d0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p11> ; data: {
    projectId = 372004;
    taskId = 340006;
    personWatchers =     (
        "0xf0bf440 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WWPerson/p1>"
    );
}

And the only one object returned at third line is:

<WQPKTeamTask: 0x1b92fcc0> (entity: WQPKTeamTask; id: 0x1b9300f0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p9> ; data: {
    projectId = 372004;
    taskId = 338001;
    personWatchers =     (
        "0xf0bf440 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WWPerson/p1>"
    );
}

Printing description of allTasks:

<_PFArray 0xf30b9a0>(
<WQPKTeamTask: 0xf3ab9d0> (entity: WQPKTeamTask; id: 0xf3cda40 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p6> ; data: <fault>),
<WQPKTeamTask: 0xf315720> (entity: WQPKTeamTask; id: 0xf3c23a0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p7> ; data: <fault>),
<WQPKTeamTask: 0xf3a1ed0> (entity: WQPKTeamTask; id: 0xf3cda30 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p8> ; data: <fault>),
<WQPKTeamTask: 0x1b92fcc0> (entity: WQPKTeamTask; id: 0x1b9300f0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p9> ; data: {
    projectId = 372004;
    taskId = 338001;
    personWatchers =     (
        "0xf0bf440 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WWPerson/p1>"
    );
}),
<WQPKTeamTask: 0xf325e50> (entity: WQPKTeamTask; id: 0xf343820 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p10> ; data: <fault>),
<WQPKTeamTask: 0xf3f6130> (entity: WQPKTeamTask; id: 0xf3cb8d0 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WQPKTeamTask/p11> ; data: {
    projectId = 372004;
    taskId = 340006;
    personWatchers =     (
        "0xf0bf440 <x-coredata://CFFD3F8B-E613-4DE8-85AA-4D6DD08E88C5/WWPerson/p1>"
    );
})
)

---

UPDATE 1

If I call the same interface fetchTasksWatchedByMeOfProject: in:

#pragma mark - NSFetchedResultsController Delegate

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{

I will get 'two objects' as well.

UPDATE 2

I've tried:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(ANY personWatchers == %@) AND (projectId == %d)", currentLoginUser, projectId];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(ANY personWatchers.personId == %@) AND (projectId == %d)", currentLoginUserId, projectId];

Still the same result.

UPDATE 3

I've checked the save:&error, error is nil.

Answer 1

I've figured out this problem today with my teammates.

If you create a to-many relationship without inverse relationship, for example, Task has a to-many relationship watchers to Person, but Person doesn't have a inverse one to Task, then the relationship field watchers will be put in the Person table instead of a middle/mapping table.

Under this condition, my adding a Person p1 into the Task t1's watchers will update the watchers filed to 1 in the Person table.

Then, add Person p1 to the Task t2 as well, the watchers field will be update to 2 like below:

So, one Person can only point to one Task!

By adding a inverse relationship from Person to Task can walk around this problem.

Answer 2

What is being saved?

What happens when you print out the -[NSManagedObjectContext updatedObjects] before the save?

What does the final predicate look like? Can you print the description of the NSFetchRequest?