Display Core Data entity records with relationship 1:M

问题

I am having big issues displaying records from my entity Product and OrderItems. This is one to Many relationships.

I added records to Product entity without any problem and I perform OrderItem entry in the following function:

     
     - (IBAction)cmdSave:(id)sender {

          self.product.productName = self.txtProductName.text;

          NSManagedObjectContext *context =[self managedObjectContext];
          OrderItems *oi=
          [NSEntityDescription  
          insertNewObjectForEntityForName:@"OrderItems"  inManagedObjectContext:context];

          [oi setValue:[NSNumber numberWithInteger:[self.txtQty.text integerValue]] forKey:@"ordQty"];
          [oi setValue:[NSNumber numberWithInteger:[self.txtPrice.text integerValue]] forKey:@"price"];
          [oi setValue:[NSNumber numberWithInteger:[self.txtTotal.text integerValue]] forKey:@"total"];
          [oi setOrders:self.product];

           NSError *error = nil;
           if (![context save:&error]) {
           NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
           abort();
          }
           [self.navigationController popViewControllerAnimated:YES];
     }

This seems ok and my biggest issue is display all order items for each Product. The relationship Product ====> OrderItems is:product and the inverse is orders. OrderItems ===>Product is: orders and inverse is product.

I try to display for fetchedResult

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    // Configure the cell...
      Product *prod = [self.fetchedResultsController objectAtIndexPath:indexPath];

  *********************
     //I wanted to connect to relationship object and get all orders but I get Incompatible   pointer types initializing 'OrderItems *_Strong ' with an expression of type NSSet.

   ******any ideas? 
    OrderItems *order=prod.product;
    **************************************

    cell.textLabel.text =prod.productName;
    cell.detailTextLabel.text =[NSString stringWithFormat:@"%@",order.price];



    return cell;
}

I know the relationship object in product in Product is NSSet as below:

     @interface Product : NSManagedObject

     @property (nonatomic, retain) NSString * productName;
     @property (nonatomic, retain) NSNumber * qty;
     @property (nonatomic, retain) NSSet *product;
     @end

     @interface Product (CoreDataGeneratedAccessors)

     - (void)addProductObject:(NSManagedObject *)value;
     - (void)removeProductObject:(NSManagedObject *)value;
     - (void)addProduct:(NSSet *)values;
     - (void)removeProduct:(NSSet *)values;

     @end

I have done the same way in different program but I don't know really why.

Any help or advice would be much appreciated!

回答1:

Incompatible pointer types initializing 'OrderItems *_Strong ' with an expression of type NSSet.

It's pretty straightforward. You almost seem to know. The problem is:

Product *prod = [self.fetchedResultsController objectAtIndexPath:indexPath];
OrderItems *order=prod.product;

You're assigning a value to a pointer of type OrderItems, and the thing you're assigning is prod.product. But what's that? It's an NSSet:

 @property (nonatomic, retain) NSSet *product;

That's why you get that message. You have a pointer to NSSet and you're trying to assign it to a pointer to OrderItems. I don't know what OrderItems is, but it's not an NSSet. You can make that assignment, but you can't expect it to work properly.

I have done the same way in different program but I don't know really why.

Either you did things differently in other apps, or you got the same message there that you're getting here.

来源：https://stackoverflow.com/questions/20157803/display-core-data-entity-records-with-relationship-1m