将子实体加载到核心数据中的托管对象

Question

我认为这是错误的，它只加载一个汽车零件： 此方法采用两个数组，一个包含汽车名称，一个包含零件，创建一辆新车，并将汽车零件添加到其中，然后将汽车保存到核心数据中。 （目前不适合这种方式）

for (int i=0; i<[massiveArray count]; i++) {
    //create a new car and part
        Car*newCar =(Car*)[NSEntityDescription insertNewObjectForEntityForName:@"Car" inManagedObjectContext:[self managedObjectContext]];
        CarPart *part =[NSEntityDescription insertNewObjectForEntityForName:@"CarPart" inManagedObjectContext:[self managedObjectContext]];

//set car title to string title in array of titles
        [newCar setValue:[massiveArray objectAtIndex:i] forKey:@"name"];
        //go through car parts array and add all new parts for that specific car
        for (int i=0; i<[partNamesArray count]; i++) {
            [part setValue:[partNamesArray objectAtIndex:i] forKey:@"name"];
            [newCar addToCarPartObject:part];
//save each part??? I think this is wrong
            [self.managedObjectContext save:nil];
        }
//Save new car
        [self.managedObjectContext save:nil];
    }

Answer 1

我知道这里发生了什么。

您需要在每个零件的核心数据中插入一个新零件对象。就像现在一样，您只制作一个部分对象，然后在 for 循环中覆盖它。您的代码应该类似于此...

for (int i=0; i<[massiveArray count]; i++) {
    //create a new car and part
    Car *newCar = [NSEntityDescription insertNewObjectForEntityForName:@"Car" inManagedObjectContext:[self managedObjectContext]];

    //set car title to string title in array of titles
    [newCar setValue:[massiveArray objectAtIndex:i] forKey:@"name"];

    //go through car parts array and add all new parts for that specific car
    for (int i=0; i<[partNamesArray count]; i++) {
        CarPart *part =[NSEntityDescription insertNewObjectForEntityForName:@"CarPart" inManagedObjectContext:[self managedObjectContext]];
        [part setValue:[partNamesArray objectAtIndex:i] forKey:@"name"];
        [newCar addToCarPartObject:part];
    }
}
//Save the entire context (all pending changes to cars and their parts)
[self.managedObjectContext save:nil];

正如我在上面的评论中所说，我建议将保存移到循环之外。

另一个更易于阅读代码的建议。在简单的 for 循环中枚举数组时，尝试类似...

for (NSString *carTitle in massiveArray) {
    /* Now do your stuff in here... 'carTitle' will be different during 
     * each pass of the loop. No need to increment an i variable or grab 
     * the object from the array on each pass. 
     */
}