一对多的神奇记录

Posted 2023-03-05

【中文标题】一对多的神奇记录

【英文标题】：Magical record one-to-many

【发布时间】：2015-09-08 10:17:05

【问题描述】：

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！

【问题讨论】：

作为一个局外人，我喜欢这个标题和介绍。神奇的记录、核心数据和关系问题：P

【参考方案1】：

首先您需要在编辑 xcdatamodel 文件时将关系设置为一对多

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

【讨论】：

1）我创建了从部分到产品的关系并设置了一对多 2）当我尝试像这样保存数据时，它没有保存，也许它不正确？当我保存时一切正常 3) NSArray* products = section.products.array;那里没有数组

抱歉，回复晚了。你能贴一张你的 xdatamodel 的图片吗？

First 和 Second

section 与 products 有关系 - 对很多，product to section 有关系 - to one。对吗？

解决了我在 didSelectRowAtIndexPath 中的问题： Section *section = section[indexPath.row]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"section == %@", section]; NSArray *products = [Product MR_findAllSortedBy:@"name" 升序：YES withPredicate:predicate];