Question

我有以下基本问题：

我有两个实体，人和部门。

在添加我要检查的新人之前，该部门尚未存在，如果存在，则将新人员链接到现有部门。

使用新的部门关系进行简单插入：

    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];

最后一行是联系 - 没关系。

但是，如果我想在执行上面的代码后执行以下操作，那该怎么办？

    [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];

简而言之，我的问题是表部门的重复条目。

也许有人知道一个好的CoreData教程，这对于具有高级SQL知识的初学者是有益的。（在Google上搜索或阅读开发人员文档数小时并没有那么有用，因为我认为:)）

对我来说，作为初学者，现在重要的是我是否采用正确的方式，有人可以证实这一点吗？

谢谢和问候，

的Matthias

Answer 1

您在if/else语句中定义了部门变量，然后在其外部使用了另一个变量。尝试将if更改为：

[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checkForExistingDepartment的代码，但我们无法帮到你。。

Answer 2

对不起，检查功能如下：

- (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];
}

CoreData - 向现有实体添加新关系

2 个答案: