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CoreData双向关系/删除规则

双向关系

双向的时候,只用指定一边,另外一边自动指定,比如,如果一个帐号只有一个联系人,而一个联系人对应一个帐号的话,那么帐号表和联系人表就是一一对应的关系,将他们指定为双向的,如下面将cnt1.act = act1; cnt2.act = cnt2;则act1.cnt和act2.cnt也是有值的。注释掉的两句可有可无。

删除规则

这里将Account表下面的cnt的删除规则设定为cascade,则在删除act1的时候,cnt1也被删除了。而Contact表没有将它下面的act的删除规则设置为cascade,在删除cnt1的时候,act1还存在。

一对多的关系

上面假设一个帐号只有一个联系人是不合理的,那只是一种假设,一般都是一个帐号下面有很多联系人,这就是一对多的关系,上面的两个法则也适用于这种关系,也就是说帐号下面的cnt设置为cascade,删除一个帐号时,它所有的联系人也被删除了,而联系人表下面的act设置为nullify,当删除一个联系人的时候帐号表没有变化。

Account *act1 = [NSEntityDescription insertNewObjectForEntityForName:@"Account" inManagedObjectContext:self.managedObjectContext];
act1.passport = @"passport1";
act1.password = @"password1";
Account *act2 = [NSEntityDescription insertNewObjectForEntityForName:@"Account" inManagedObjectContext:self.managedObjectContext];
act2.passport = @"passport2";
act2.password = @"password2";

Contact *cnt1 = [NSEntityDescription insertNewObjectForEntityForName:@"Contact" inManagedObjectContext:self.managedObjectContext];
cnt1.passport = @"passport1";
cnt1.nickname = @"nickname1";
cnt1.act = act1;
Contact *cnt2 = [NSEntityDescription insertNewObjectForEntityForName:@"Contact" inManagedObjectContext:self.managedObjectContext];
cnt2.passport = @"passport2";
cnt2.nickname = @"nickname2";
cnt2.act = act2;

// act1.cnt = cnt1;
// act2.cnt = cnt2;


[self.managedObjectContext save:nil];



// Delete a Account
NSFetchRequest *fr = [[NSFetchRequest alloc] init];
NSEntityDescription *ed = [NSEntityDescription entityForName:@"Account" inManagedObjectContext:self.managedObjectContext];
[fr setEntity:ed];

NSArray *ary = [self.managedObjectContext executeFetchRequest:fr error:nil];
for (Account *act in ary) {
//NSLog(@"%@ %@ %@ %@", act.passport, act.password, act.cnt.passport, act.cnt.nickname);
if ([act.passport isEqualToString:@"passport2"]) {
NSLog(@"DEL passport2");
[self.managedObjectContext deleteObject:act];
}
}

[self.managedObjectContext save:nil];

// Delete a Contact
NSFetchRequest *fr = [[NSFetchRequest alloc] init];
NSEntityDescription *ed = [NSEntityDescription entityForName:@"Contact" inManagedObjectContext:self.managedObjectContext];
[fr setEntity:ed];

NSArray *ary = [self.managedObjectContext executeFetchRequest:fr error:nil];
NSLog(@"%d", ary.count);
for (Contact *cnt in ary) {
//NSLog(@"%@ %@ %@ %@", act.passport, act.password, act.cnt.passport, act.cnt.nickname);
if ([cnt.nickname isEqualToString:@"nickname1"]) {
NSLog(@"DEL nickname1");
[self.managedObjectContext deleteObject:cnt];
}
}

[self.managedObjectContext save:nil];




// From Account
NSFetchRequest *fr = [[NSFetchRequest alloc] init];
NSEntityDescription *ed = [NSEntityDescription entityForName:@"Account" inManagedObjectContext:self.managedObjectContext];
[fr setEntity:ed];

NSArray *ary = [self.managedObjectContext executeFetchRequest:fr error:nil];
for (Account *act in ary) {
NSLog(@"%@ %@ %@ %@", act.passport, act.password, act.cnt.passport, act.cnt.nickname);
}


// From Contact
NSFetchRequest *fr = [[NSFetchRequest alloc] init];
NSEntityDescription *ed = [NSEntityDescription entityForName:@"Contact" inManagedObjectContext:self.managedObjectContext];
[fr setEntity:ed];

NSArray *ary = [self.managedObjectContext executeFetchRequest:fr error:nil];
for (Contact *cnt in ary) {
NSLog(@"%@ %@ %@ %@", cnt.passport, cnt.nickname, cnt.act.passport, cnt.act.password);
}

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posted on 2012-03-01 19:50  pengyingh  阅读(3433)  评论(0编辑  收藏  举报

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