CoreData - 为现有实体添加新关系

Question

我有以下基本问题：

我有两个实体，人员和部门。

在添加新人之前，我想检查部门是否已经存在，如果有，请将新人员链接到现有部门。

简单的插入一个新的部门关系：

Department *department = (Department *)[NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.context]; 
    department.groupName = @"Office of Personnel Management"; 

    Person *person1 = (Person *)[NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.context]; 
    person1.name = @"John Smith"; 
    person1.birthday = [self dateFromString:@"12-1-1901"]; 
    person1.department = department; 

    Person *person2 = (Person *)[NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.context]; 
    person2.name = @"Jane Doe"; 
    person2.birthday = [self dateFromString:@"4-13-1922"]; 
    person2.department = department; 

    department.manager = person1; 
    department.members = [NSSet setWithObjects:person1, person2, nil]; 

的最后一行，使联动 - 这是确定。

但如果我要做到以下几点，上面的代码执行后什么：

[self checkForExistingDepartment:@"Office of Personnel Management"]; 
    if(self.existingDepartment) { 

     // here is my Problem number 1: 
     // department = ??? 
     (NSEntityDescription *) department = self.existingDepartment; 

    } else { 
     Department *department = (Department *)[NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.context]; 
     department.groupName = @"Office of Personnel Management"; 

    } 

    Person *person1 = (Person *)[NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.context]; 
    person1.name = @"John Smith the second one"; 
    person1.birthday = [self dateFromString:@"12-1-1901"]; 
    person1.department = department; 

    // former line for adding new: department.members = [NSSet setWithObjects:person1, nil]; 

    // and here is my problem number 2: 
    // I think I need something like: [NSSet addObjects:person1, nil]; 

总之形式我的问题是重复的表项部门。

也许有人知道一个好的CoreData教程，这对于初学者来说具有先进的SQL知识。 （搜索谷歌或阅读开发文档数小时是没有那么有用，因为我认为:)）

对于我作为一个初学者，现在是否很重要，无论我是否正确的方式，是否有人可以证实这一点？

感谢和问候，

马蒂亚斯

Answer 1

你定义if/else语句中的部门变量，然后用它的一个不同之外。试着改变你的if的样子：

[self checkForExistingDepartment:@"Office of Personnel Management"]; 
if(self.existingDepartment) { 
    department = self.existingDepartment; 
} else { 
    department = (Department *)[NSEntityDescription insertNewObjectForEntityForName:@"Department" inManagedObjectContext:self.context]; 
    department.groupName = @"Office of Personnel Management"; 
} 

虽然没有看到代码checkForExistingDepartment我们不能帮你了。 。 。

Answer 2

对不起，该校验功能如下：

- (void) checkForExistingDepartment:(NSString *)searchDepartment { 
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Department" initManagedObjectContext:self.context]; 
    [fetchRequest setEntity:entity]; 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"country" ascending:YES selector:nil]; 
    NSArray *descriptors = [NSArray arrayWithObject:sortDescriptor]; 
    [fetchRequest setSortDescriptor:descriptors]; 

    NSString *query = searchDepartment; 
    if(query && query.length) { 
     fetchRequest.predicate = [NSPredicate predicatWithFormat:@"country contains[cd] %@", query]; 
    } 

    NSError *error; 
    self.fetchedResultsController = [[NSFetchedResultsController alloc] 
            initWithFetchRequest:fetchRequest 
            managedObjectContext:self.context 
             sectionNameKeyPath:@"section" 
               cacheName:@"Root"]; 
    self.fetchedResultsController.delegate = self; 
    [self.fetchedResultsController release]; 
    if(![[self fetchedResultsController] performFetch:&error]) { 
     NSLog(@"Error %@", [error localizedDescription]); 
    } 

    self.existingDepartment = [self.fetchedResultsController objectAtIndexPath:0]; 
    [fetchRequest release]; 
    [sortDescriptor release]; 
}