需要帮助在iPhone的核心数据多对多关系 [英] Need help with many-to-many relationships in core data for iPhone

问题描述

我在我目前的项目中来了一个路障。我基本上有一个应用程序，就像Core Data Recipe应用程序...
这是我的.xcdatamodel中的基本结构

实体：
String：name
类别：category< ---- to-many relationship

实体：类别
String：name
餐厅：餐厅< ---- to-many关系
所以基本上，一个餐厅可以有多个类别...
和有一个const数量的预定义类别..
例如：
餐厅：
名称：Chili's
分类：外卖，家庭用餐

外卖和家庭餐饮是10的不同可能的餐厅类别中的2。
我如何做这个..我看过sqllite数据库，我有我的ZRestaurant和ZCategory表+连接表为他们...我有两个数据...

如何设置我的餐厅Catagory与不同的值？然后如何取回他们？

感谢所有！
Kurt

解决方案

确定，在过去2天的工作后，我终于想出了我的解决方案，实际上是亚历克斯和威尔斯的建议之间的混合...谢谢你们两个！

这是我有...

  NSManagedObjectContext * context = [restaurant managedObjectContext]; 
 
 
 NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init]; 
 [fetchRequest setEntity：[NSEntityDescription entityForName：@CategoryinManagedObjectContext：context]]; 
 NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@nameascending：YES]; 
 NSArray * sortDescriptors = [[NSArray alloc] initWithObjects：& sortDescriptor count：1]; 
 [fetchRequest setSortDescriptors：sortDescriptors]; 
 
 NSError * error = nil; 
 NSArray * possibleCategories = [context executeFetchRequest：fetchRequest error：& error]; 
 
 categoryArray = [[NSMutableArray alloc] initWithArray：possibleCategories]; 
 
 currentCategories = [restaurant valueForKeyPath：@categories]; 
 
 [restaurant addCategoriesObject：（Category *）[possibleCategories objectAtIndex：15]]; 
 
 [currentCategories addObject：（Category *）[categoryArray objectAtIndex：15]]; 
  

然后我这样保存

   - （void）save {
 NSLog（@EditCatagoriesTableViewController  -  save）; 
 
 NSSet * myCategorySet = [[NSSet alloc] initWithSet：currentCategories]; 
 
 NSError * error = nil; 
 
 [restaurant addCategories：myCategorySet]; 
 
 
 error = nil; 
 if（！[restaurant.managedObjectContext save：& error]）{
 //处理错误
 NSLog（@restaurant  - 未解决的错误％@，％@，错误，[错误userInfo]）; 
 exit（-1）; // Fail 
} 
} 
  

>

非常感谢您的帮助。

-Kurt

I have come to a roadblock in my current project. I basically have an app that is much like the Core Data Recipe app... Here is the basic structure I have in my .xcdatamodel

Entity: Restaurant String: name Category: category <---- to-many relationship

Entity: Category String: name Restaurant: restaurant <---- to-many relationship So basically, a Restaurant can have multiple categories... And there are a const number of predefined Categories.. For example: Restaurant: Name: Chili’s Categories: Take Out , Family Dining

"Take Out" and "Family Dining" are 2 of 10 different possible Restaurant Categories. How do I go about doing this.. I have looked at the sqllite database and I have my ZRestaurant and ZCategory table + the join table for both of them... I have data in both...

How do I go about setting my Restaurants Catagory with the different values? and then how do I fetch them back?

Thanks all! Kurt

解决方案

OK, After working on this for the past 2 days I finally came up with my solution which was actually a mix between Alex and Wills suggestions... Thank you to both of you!!

Here is what I have...

 NSManagedObjectContext *context = [restaurant managedObjectContext];


NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:@"Category" inManagedObjectContext:context]];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:&sortDescriptor count:1];
[fetchRequest setSortDescriptors:sortDescriptors];

NSError *error = nil;
NSArray *possibleCategories = [context executeFetchRequest:fetchRequest error:&error];

categoryArray = [[NSMutableArray alloc] initWithArray:possibleCategories];

currentCategories = [restaurant valueForKeyPath:@"categories"];

[restaurant addCategoriesObject:(Category *)[possibleCategories objectAtIndex:15 ]];

[currentCategories addObject:(Category*)[categoryArray objectAtIndex:15]];

and then I save like this

- (void)save{
    NSLog(@"EditCatagoriesTableViewController - save");

    NSSet* myCategorySet = [[NSSet alloc] initWithSet:currentCategories];

    NSError *error = nil;

    [restaurant addCategories:myCategorySet];


    error = nil;
    if (![restaurant.managedObjectContext save:&error]) {
        // Handle error
        NSLog(@"restaurant - Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    }       
}

And that does it!

Thank you so much for the help you two!!!

-Kurt

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