[英]fetch coredata relationship
我想知道如何從我的coredata關系船中獲取項目。 我猜應該是字典或數組或返回的東西,這樣您就可以擁有一對多的東西。
我很迷惑,因為我知道如何寫/讀單個對象,但是這種關系讓人有些困惑。
我想我已經成功地編寫了與coredata的關系,但是現在我希望能夠閱讀它以查看我是否正確。.我已經開始為此編寫方法,但不知道該怎么做才能獲得所有這些信息出來。
這是我到目前為止的代碼..對於讀寫
- (void)writeFin:(NSArray *)recivedProjectData ItemsData:(NSArray *)itemsData {
// WRITE TO CORE DATA
NSManagedObjectContext *context = [self managedObjectContext];
for (NSDictionary *dict in recivedProjectData) {
project = [NSEntityDescription insertNewObjectForEntityForName:@"Project" inManagedObjectContext:context];
project.proNumber = [dict valueForKey:@"ProNumber"];
project.projectDescription = [dict valueForKey:@"Description"];
// project.items = [dict valueForKey:@""]; // this is the relationship for project
}
for (NSDictionary *dict in itemsData) {
items = [NSEntityDescription insertNewObjectForEntityForName:@"Items" inManagedObjectContext:context];
items.Number = [dict valueForKey:@"Number"];
items.Description = [dict valueForKey:@"Description"];
items.comment = [dict valueForKey:@"Comment"];
items.project = project; // this is the relationship for items
[project addItemsObject:items];
}
NSError *error = nil;
if (![__managedObjectContext save:&error]) {
NSLog(@"There was an error! %@", error);
}
else {
NSLog(@"created");
}
}
- (NSMutableArray *)readFin {
NSManagedObjectContext *context = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Project" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSError *error;
NSMutableArray *projectDictionaryArray = [[NSMutableArray alloc] init];
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (ProjectList *projectList in fetchedObjects) {
NSMutableDictionary *tempProjectDictionaryArray = [[ NSMutableDictionary alloc] init];
[tempProjectDictionaryArray setObject:project.proNumber forKey:@"ProNumber"];
[tempProjectDictionaryArray setObject:project.description forKey:@"Description"];
[tempProjectDictionaryArray setObject:project.projectID forKey:@"ProjectID"];
[projectDictionaryArray addObject:tempProjectDictionaryArray];
}
return projectDictionaryArray;
}
因此,請重申一下,我想知道A,我的寫方法看起來還好嗎? B,如何從核心數據中獲取/讀取關系對象。
任何幫助將不勝感激。
Core Data中的關系不是對象,它是一個屬性,恰好對應於模型中的另一個對象,而不僅僅是一個死胡同。 就我所知,您已經到了檢查您的關系是否正常的大部分方法-您需要做的是在項目列表中再添加一行
[tempProjectDictionaryArray setObject: project.items forKey:@"items"];
您將添加的對象將是NSSet。 完成設置后,您可以通過如下循環檢查事物是否應該存在
NSSet itemsForProject = projectDictionaryArray[someIndex][@"items"]
for (Item* currItem in [itemsForProject allObjects]) {
//access some property of the current item to make sure you have the right ones -- \
description for example
NSLog(@"%@", item.description);
}
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