title: MagicalRecord Find(All) doesn't find objects from relationships sometimes
body: <p>The objects from relationship just gone when I close the simulator and reopen it or push and pop some view controllers. I still can get the objects when I first save the objects to core data. </p>
  
  <p>This is the code to save objects to core data:</p>
  
  <pre><code>for (NSDictionary *obj in results) {
      Stock *stock = [Stock MR_createEntity];
      stock.name = obj[@"name"];
      NSArray *categories = obj[@"categories"];
      if ([categories count] &gt; 0) {
          for (NSDictionary *category in categories) {
              StockCategory *stockCategory = [StockCategory MR_createEntity];
              stockCategory.categoryId = category[@"_id"];
              stockCategory.name = category[@"name"];
              [stock addCategoriesObject:stockCategory];
          }
      }
  }
  [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) {
      self.stocks = [Stock MR_findAllSortedBy:@"createdDate" ascending:NO];
      dispatch_async(dispatch_get_main_queue(), ^{
          [SVProgressHUD dismiss];
          [self.tableView reloadData];
      });
  }];
  </code></pre>
  
  <p>Below code is to retrieve object from core data:</p>
  
  <pre><code>self.stocks = [Stock MR_findAllSortedBy:@"createdDate" ascending:NO];
  dispatch_async(dispatch_get_main_queue(), ^{
      [SVProgressHUD dismiss];
      [self.tableView reloadData];
  });
  </code></pre>
  
  <p>If I close the simulator, and re launch it, I get objects from core data but the stock's StockCategory array is empty. I recall it when I first save the stock to the core data, the stock's StockCategory array is not empty. Why when I relaunch the simulator, the objects from relationships just gone.</p>
  
  <p>The model:
  Stock.h</p>
  
  <pre><code>@class StockCategory;
  
  @interface Stock : NSManagedObject
  
  @property (nonatomic, retain) NSString * name;
  
  @property (nonatomic, retain) NSSet *categories;
  @end
  
  @interface Stock (CoreDataGeneratedAccessors)
  
  - (void)addCategoriesObject:(StockCategory *)value;
  - (void)removeCategoriesObject:(StockCategory *)value;
  - (void)addCategories:(NSSet *)values;
  - (void)removeCategories:(NSSet *)values;
  
  @end
  </code></pre>
  
  <p>StockCategory.h</p>
  
  <pre><code>@class Stock;
  
  @interface StockCategory : NSManagedObject
  
  @property (nonatomic, retain) NSString * name;
  @property (nonatomic, retain) Stock *stock;
  
  @end
  </code></pre>