如何管理Core Data中的一对多关系？(How to manage one-to-many relationship in Core Data?)

 我很难搞清楚Core Data如何处理数据库的一些事情。 我将用一个具体的例子来解释我的问题： 
 
 我们只是说我们有以下架构，其中有部门拥有众多帐户（我们的地址）。 
 
 我使用编辑器创建了我的Core Data文件。 在CachedDepartment类中，我添加了必要的属性，并且我创建了一个to-many关系，并且我已经选择了“Inverse”到我的CachedAccount的Department属性.CacheAccount也有属性，并且关系与“解决“CachedDepartment的关系”。 
 
 我有以下来源（我给你2个头文件。其余的没有任何兴趣）： 
 
@interface CachedAccount : NSManagedObject {
@private
}
@property (nonatomic, retain) NSNumber * accountID;
@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) CachedDepartment *department;
@end

@class CachedAccount;

@interface CachedDepartment : NSManagedObject {
@private
}
@property (nonatomic, retain) NSString * departmentID;
@property (nonatomic, retain) NSString * departmentName;
@property (nonatomic, retain) NSSet *addresses;
@end

@interface CachedDepartment (CoreDataGeneratedAccessors)

- (void)addAddressesObject:(CachedAccount *)value;
- (void)removeAddressesObject:(CachedAccount *)value;
- (void)addAddresses:(NSSet *)values;
- (void)removeAddresses:(NSSet *)values;

@end
 
 现在的问题是： 
 - 如何创建帐户和部门对象，以便建立一对多的关系？ 

 - 我应该如何处理CoreDataGeneratedAccessors？创建之后，我应该调用CachedDepartment的-addAddressesObject函数，还是需要创建类似anAccount.department = aDepartment的东西，那就是它？ 

 - 在创建对象的每种情况下，如何确保向部门添加地址不会创建地址的双重实例并存储它？ 

 
 我将不胜感激任何见解。 
 
 编辑： 
 
 是否应为CachedDepartment实体插入新对象，如下所示： 
 
NSManagedObject *cachedDepartment= [NSEntityDescription
    insertNewObjectForEntityForName:@"CachedDepartment" 
    inManagedObjectContext:[self managedObjectContext]];
/*
set values for failedBankInfo here
*/
NSError *error;
if (![context save:&error]) {
    NSLog(@"The following error occured: %@", [error localizedDescription]);
}
 
 然后将为cachedAccounts添加一条新记录，该记录将与新插入的cachedDepartment对象保持一对多的关系，如下所示： 
 
NSManagedObject *cachedAccounts = [NSEntityDescription
    insertNewObjectForEntityForName:@"CachedAccounts" 
    inManagedObjectContext:[<b>cachedDepartment managedObjectContext</b>]];
    /*
    set values for failedBankInfo here
    */
//setting the one-to-many relationship
[cachedDepartment addCachedAccountObject:cachedAccount];
[cachedAccount setCachedDepartment:cachedDepartment];
//
NSError *error;
if (![context save:&error]) {
    NSLog(@" couldn't save: %@", [error localizedDescription]);

I am having a hard time figuring out some things about how Core Data handles its database. I will explain my problems with a concrete example:
 
Let's just say that we have the following schema where there are departments which hold numerous accounts (our addresses).
 
I have created my Core Data file using the editor. In the CachedDepartment class, I have added the necessary attributes, and I have created a to-many relationship, and I have selected "Inverse" to the "Department property of my CachedAccount. CacheAccount also has attributes, and a relationship inverse to the "addresses" relationship of CachedDepartment.
 
I have the following sources (I give you the 2 header files. The rest contain nothing of interest):
 
@interface CachedAccount : NSManagedObject {
@private
}
@property (nonatomic, retain) NSNumber * accountID;
@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) CachedDepartment *department;
@end

@class CachedAccount;

@interface CachedDepartment : NSManagedObject {
@private
}
@property (nonatomic, retain) NSString * departmentID;
@property (nonatomic, retain) NSString * departmentName;
@property (nonatomic, retain) NSSet *addresses;
@end

@interface CachedDepartment (CoreDataGeneratedAccessors)

- (void)addAddressesObject:(CachedAccount *)value;
- (void)removeAddressesObject:(CachedAccount *)value;
- (void)addAddresses:(NSSet *)values;
- (void)removeAddresses:(NSSet *)values;

@end
 
And now the questions: 
 -- How should an account and department objects be created so that a one-to-many relationship will be established?

 -- What should I do with CoreDataGeneratedAccessors?After creation, should I call the -addAddressesObject function of CachedDepartment or I will need to make something like anAccount.department = aDepartment and that's it?

 -- In each case when creating objects how can I make sure that adding an address to a department won't create a double instance of the address and store it?

 
I would appreciate any insights on this.
 
EDIT:
 
Should inserting new objects for CachedDepartment entity look like the following code:
 
NSManagedObject *cachedDepartment= [NSEntityDescription
    insertNewObjectForEntityForName:@"CachedDepartment" 
    inManagedObjectContext:[self managedObjectContext]];
/*
set values for failedBankInfo here
*/
NSError *error;
if (![context save:&error]) {
    NSLog(@"The following error occured: %@", [error localizedDescription]);
}
 
then would adding a new record for the cachedAccounts which will be in one-to-many relationship with the newly inserted cachedDepartment object be something like that:
 
NSManagedObject *cachedAccounts = [NSEntityDescription
    insertNewObjectForEntityForName:@"CachedAccounts" 
    inManagedObjectContext:[<b>cachedDepartment managedObjectContext</b>]];
    /*
    set values for failedBankInfo here
    */
//setting the one-to-many relationship
[cachedDepartment addCachedAccountObject:cachedAccount];
[cachedAccount setCachedDepartment:cachedDepartment];
//
NSError *error;
if (![context save:&error]) {
    NSLog(@" couldn't save: %@", [error localizedDescription]);

原文：https://stackoverflow.com/questions/8723792