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POiOS - core data - save unsuccessful after using remove methods in NSManagedObject Subclasses
 

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  1. POiOS - core data - save unsuccessful after using remove methods in NSManagedObject Subclasses
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    <p><strong>Overview:</strong></p> <ol> <li>I remove an NSManagedObject using the remove methods provided in the autogenerated NSManagedObject subclass </li> <li>Then I attempt to save the database</li> <li>The database save is unsuccessful.</li> </ol> <p>.</p> <pre><code> - (void)removeEmployees:(NSSet *)values; //Auto generated method in Department.h </code></pre> <p>However adding of an NSManagedObject using the add method allows the database to be saved successfully</p> <pre><code> - (void)addEmployeesObject:(Employee *)value; //Auto generated method in Department.h - works fine </code></pre> <p><strong>Note:</strong> I am using NSManagedObject subclasses generated by XCode.</p> <p><strong>Entity Details:</strong></p> <ul> <li>I have 2 tables (entities) namely "Employee" and "Department"</li> <li>One department can contain multiple employees</li> <li>One employee can only belong to one department</li> </ul> <p><strong>Relationship Details:</strong></p> <ul> <li>Relationship from an "Employee" to "Department" is a One to One relationship and is called "whichDepartment". Delete rule is Nullify</li> <li>Relationship from an "Department" to "Employee" is a Many to One relationship and is called "employees". Delete rule is Cascade</li> </ul> <p><strong>Problem:</strong></p> <p>"Department" class has a method called as mentioned below, after I use this method, the database save is not successful</p> <pre><code>(void)removeEmployees:(NSSet *)values; //Auto generated method in Department.h //does not work </code></pre> <p><strong>Code used to Delete:</strong></p> <pre><code>- (void) removeEmployeesHavingAgeAsZeroWithDepartment: (Department*) department { NSMutableSet *employeesSetToBeRemoved = [[NSMutableSet alloc] init]; for(Employees *currentEmployee in department.employees) { if(currentEmployee.age == 0) { [employeesSetToBeRemoved addObject:currentEmployee]; } } [department removeEmployees:employeesSetToBeRemoved]; //causing the problem } </code></pre> <p><strong>Code used to save the database</strong></p> <pre><code>[self.database saveToURL:self.database.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:^(BOOL success) {NSLog(@"DB saved");}]; </code></pre> <p><strong>Questions:</strong></p> <ol> <li>Why is it that the saving the Database not successful after using the remove methods?</li> <li>Do I need to implement this method ? currently i don't see any implementation for this method, I can only find it in the header file.</li> <li>Are my relationships (inverse, delete rules, etc) set up correctly ?</li> </ol> <p><strong>Answer:</strong></p> <ul> <li>Pls refer to Jody's answer and comments (May 17 at 4:39), it is explained well as how to debug the problem and find the root cause</li> </ul>
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    1. COSo its not crashing, it just doesn't remove items? Have you tried saving the context once you call removeEmployees? I know there is a bug in the auto-generated code if you add/remove items from an NSOrderedSet but this should work fine.
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    2. COIt doesn't crash, but it doesn't remove the records. Adding alone seems to work as mentioned above
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