Question

我正在Entity使用属性EY_Appliances，applianceId，applianceName，watts调用amountPerWatts。此外我还有像这样的数组：

Prefrence.h

#define APPLIANCENAME_ARRAY @[@"Fridge",@"Microwave",@"Mixie",@"Roti Maker",@"Coffee Machine",@"Dish Washer",@"Wet Grinder",@"Electric Stove",@"Ceiling Fan",@"TV",@"Table Fan",@"Tubelight",@"Bulb",@"AC",@"Vacuum Cleaner",@"CFL",@"LED",@"Washing Machine",@"Toaster",@"Room Heater",@"Iron",@"Motor",@"Water Heater",@"Inverter / UPS",@"Air Cooler",@"Steamer / Air Fryer",@"Hair Dryer",@"Laptop",@"PC",@"Tablet",@"Router / Modem",@"Home Theatre",@"Projector",@"PS3/PS4/XBOX"]

#define WATTS_ARRAY @[@"120",@"1000",@"700",@"30",@"167",@"810",@"180",@"150",@"75",@"120",@"75",@"40",@"60",@"1200",@"1400",@"20",@"6",@"300",@"1000",@"1600",@"1400",@"2400",@"1000",@"67",@"173",@"585",@"1026",@"15",@"150",@"4",@"4",@"17",@"240",@"10"]

DataAccessHandler.m

-(void)storeApplianceDetailsToEntity
{
NSManagedObjectContext *context = [self managedObjectContext];


for (int i=0; i<APPLIANCENAME_ARRAY.count; i++)
{
    NSManagedObject *object = [NSEntityDescription insertNewObjectForEntityForName:@"EY_Appliances" inManagedObjectContext:context];
    [object setValue: APPLIANCENAME_ARRAY[i] forKey:@"applianceId"];
    [object setValue: APPLIANCENAME_ARRAY[i] forKey:@"applianceName"];
    [object setValue: WATTS_ARRAY[i] forKey:@"watts"];
    [object setValue: WATTS_ARRAY[i] forKey:@"amountPerWatts"];
}

NSError *error = nil;
if (![context save:&error])
{
    NSLog(@"Saving Failed with error %@", error);
}
NSLog(@"entityValue==>%@",context);

}


-(NSArray *) fetchApplianceDetailsFromEntity:(NSString *) entityName
{
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest;
NSEntityDescription *entityDescription;
NSArray *array;
fetchRequest = [[NSFetchRequest alloc] init];
entityDescription = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entityDescription];


array =   [managedObjectContext executeFetchRequest:fetchRequest error:nil];
NSLog(@"arr==>>%@",array);
return array;

}

ViewController.m

-(void)viewDidLoad
{
DataAccessHandler *dataAccess=[[DataAccessHandler alloc]init];
[dataAccess storeApplianceDetailsToEntity];
NSArray *applianceData = [dataAccess fetchApplianceDetailsFromEntity:@"EY_Appliances"];

//How to print the applianceName,If i write Like this applianceData.applianceName,it shows error…
}

1.如何打印applianceName？

2.如何设置applianceId primaryKey并将applianceId 1的值存储到34？

Answer 1

 NSDictionary  *applianceData = [dataAccess fetchApplianceDetailsFromEntity:@"EY_Appliances"];

使用关键字返回值

Answer 2

applianceData是一个数组，因此您需要通过索引

访问它

您的代码刚刚使用设备名称作为ID - 如果您只需要一个标识符，则可以使用索引i

加载会将所有内容返回到数组中 - 如果您只想加载部分数据集，则需要在fetchApplianceDetailsFromEntity中添加获取谓词

[fetch setPredicate:[NSPredicate predicateWithFormat:@"(applianceId == %@)",idString]];

如何在Coredata中获取单个属性实体值？

2 个答案: