一对多的神奇记录

Question

我正在尝试使用 CoreData 和 Magical 记录。我的人际关系有问题 所以，我有部分，每个部分都应该存储产品 我的部分.h

@class Product;

@interface Section : NSManagedObject

@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *code;
@property (nonatomic, retain) NSString *sectionId;
@property (nonatomic, retain) Product  *product;

@end

@interface Section (CoreDataGeneratedAccessors)

- (void)addProductObject:(Product *)value;
- (void)removeProductObject:(Product *)value;
- (void)addProducts:(NSSet *)values;
- (void)removeProducts:(NSSet *)values;

和 Product.h

@interface Product : NSManagedObject

@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *code;
@property (nonatomic, retain) NSString *descrpt;
@property (nonatomic, retain) NSString *imgBig;
@property (nonatomic, retain) NSString *imgSmall;

所以，我正在尝试将产品添加到这样的部分

for (int i = 0; i<[sectionResponse count]; i++) {
        _section = [Section MR_createEntity];
        _section.name       = [[sectionResponse valueForKey:@"name"] objectAtIndex:i];
        _section.code       = [[sectionResponse valueForKey:@"code"] objectAtIndex:i];
        _section.sectionId  = [[sectionResponse valueForKey:@"id"] objectAtIndex:i];

        for (int j = 0; j < productResponse.count; j++) {
            if ([_section.sectionId isEqualToString:[[productResponse valueForKey:@"section"] objectAtIndex:j]]) {
                _product = [Product MR_createEntity];
                __product.name    = [[productResponse valueForKey:@"name"] objectAtIndex:j];
                _product.descrpt = [[productResponse valueForKey:@"desc"] objectAtIndex:j];

               [_section addProductObject:_product];
            }
        }
    }

    [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];

能否请您帮助我了解如何添加产品以及以后如何检索它们？谢谢！

Answer 1

1. 首先您需要在编辑 xcdatamodel 文件时将关系设置为一对多

1. 其次，你应该这样保存数据

   [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
       ......... 
       for (int i = 0; i<[sectionResponse count]; i++) {
          _section = [Section MR_createEntity];
          _section.name       = [[sectionResponse valueForKey:@"name"] objectAtIndex:i];
         _section.code       = [[sectionResponse valueForKey:@"code"] objectAtIndex:i];
        _section.sectionId  = [[sectionResponse valueForKey:@"id"] objectAtIndex:i];
   
   for (int j = 0; j < productResponse.count; j++) {
       if ([_section.sectionId isEqualToString:[[productResponse valueForKey:@"section"] objectAtIndex:j]]) {
           _product = [Product MR_createEntity];
           __product.name    = [[productResponse valueForKey:@"name"] objectAtIndex:j];
           _product.descrpt = [[productResponse valueForKey:@"desc"] objectAtIndex:j];
   
       //   [_section addProductObject:_product];
       //   Instead of "add Product to Section", you should "set the Product's section"  
            [_product setSection:_section];
       }
   }
   }
   }];
   

3.所以该部分现在保存为 NSSet。读取一个产品的数据属于一个section。

   //Approach 1
   Section* section = [Section MR_findFirstWithPredicate:[NSPredicate predicateWithFormat:@"......."] inContext:[NSManagedObjectContext MR_defaultContext]];

  NSArray* products = section.products.array; //I assume you use "products" as the name
  //Approach 2
  Product* product = [Product MR_findFirstWithPredicate:[NSPredicate predicateWithFormat:@"section.sectionID==%@",@"D7689"] inContext:[NSManagedObjectContext MR_defaultContext]];

请随时让我跟进问题