Core data 核心数据-与对象（一）和UIImage（多）的一对多关系，存储和获取

我的目标是构建一个应用程序，其目标是： -请求（包含唯一id、客户名称、电话、电子邮件、请求信息摘要、图像列表（存储在NSMutable数组中）

我的核心数据包括：

• 请求
• 形象

对于我的请求对象，我有：

#import <Foundation/Foundation.h>

@interface BAPRequest : NSObject
@property (nonatomic, retain) NSString *requestID;
@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *email;
@property (nonatomic, retain) NSString *phone;
@property (nonatomic, retain) NSString *detail;
@property (nonatomic, retain) NSMutableArray *images;
@property (nonatomic, retain) NSDate *requestDate;
@property (nonatomic) BOOL isSent;

- (void)fetchImages;
@end

要获取所有请求，我还执行以下操作：

- (void)removeRequest:(BAPRequest*)request{
    //get delegation
    BAPAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    NSError *error;

    //init request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    //load the entity description
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Request"
                                                         inManagedObjectContext:context];
    //set the request query
    [fetchRequest setEntity:entityDescription];

    //set predicate to request to ask select specific entity with the matching line num
    NSLog(@"request id is %@", request.requestID);
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"(requestId LIKE %@)", request.requestID];
    [fetchRequest setPredicate:pred];

    //exec the command to find the object(table) from core database
    NSArray *objects = [context executeFetchRequest:fetchRequest error:&error];

    //if this object doesn't exist in the database, it must be something wrong
    if (objects == nil) {
      NSLog(@"There was an error !");
      NSLog(@"Error Info: %@", error);
    }

    //if object exist in database, take the first search object, and deletes it
    if ([objects count] > 0){
      NSManagedObject *theRequest = [objects objectAtIndex:0];
      [context deleteObject:theRequest];
    }

    [context save:&error];

    /*
    //delete existing images relates to this request first
    entityDescription = [NSEntityDescription entityForName:@"Image"
                                    inManagedObjectContext:context];
    pred = [NSPredicate predicateWithFormat:@"(self.request == %@)", request];
    [fetchRequest setPredicate:pred];
    NSArray * imageList = [context executeFetchRequest:fetchRequest error:&error];
    for (NSManagedObject *removeImageObject in imageList){
      [context deleteObject:removeImageObject];
    }
     */
  }

  #pragma mark - Convert Core Data Object to Request Object

  #pragma mark - Core Data Methods
  - (NSMutableArray *)getRequests{
    //get app delegate
    BAPAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    //get object context that's created for us
    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    //define the entities we want load to description
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Request"
                                                   inManagedObjectContext:context];

    //init request and set search query to the request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setEntity:entityDescription];

    NSError *error;
    //get objects(table) though request
    NSArray *objects = [context executeFetchRequest:fetchRequest error:&error];

    if (objects == nil){
      NSLog(@"There was an error !");
      //error handling there
      NSLog(@"Error Info: %@", error);
    }

    NSMutableArray *requests = [[NSMutableArray alloc] init];
    for (NSManagedObject *requestObj in objects){
      BAPRequest *request = [[BAPRequest alloc] init];
      request.requestID = [requestObj valueForKey:@"requestId"];
      request.name = [requestObj valueForKey:@"name"];
      request.email = [requestObj valueForKey:@"email"];
      request.phone = [requestObj valueForKey:@"phone"];
      request.detail = [requestObj valueForKey:@"detail"];
      request.requestDate = [requestObj valueForKey:@"requestDate"];
      request.isSent =  [[requestObj valueForKey:@"isSent"] boolValue];

      [request fetchImages];

      [requests addObject: requestObj];
    }

    return requests; //return the requests
  }

  - (void)saveRequest:(BAPRequest *)request{
    request.requestDate = [NSDate date];

    //get delegation
    BAPAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    NSError *error;

    BAPRequest  *theRequest = [NSEntityDescription insertNewObjectForEntityForName:@"Request"
                                                 inManagedObjectContext:context];


    //set the request obejct basics
    [theRequest setValue:request.requestID forKey:@"requestId"];
    [theRequest setValue:request.name forKey:@"name"];
    [theRequest setValue:request.email forKey:@"email"];
    [theRequest setValue:request.phone forKey:@"phone"];
    [theRequest setValue:request.detail forKey:@"detail"];
    [theRequest setValue:request.requestDate forKey:@"requestDate"];
    [theRequest setValue:[NSNumber numberWithBool:request.isSent ] forKey:@"isSent"];

    //also save its requests
    for (UIImage *img in request.images) {
      //init image object
      UIImage *newImage=[NSEntityDescription insertNewObjectForEntityForName:@"Image" inManagedObjectContext:context];
      [newImage setValue:request.requestID forKey:@"requestId"];
      [newImage setValue:UIImagePNGRepresentation(img) forKey:@"content"];
    }

    [context save:&error];  //save the object
  }
  @end

我的问题是：

我猜它根本无法获取图像。即使他们使用getRequests方法获取图像，当我尝试将请求传递到其他地方时，仍然会遇到很多问题：

• 布尔值未正确加载
• 图像为零（即使在获取时已加载）

原因是（我可能错了）当我将这些请求对象（BAPRequest*）存储到NSArray并将其传递到表视图时，当我从数组（例如[myArray objectAtIndex:0]）加载它们时，它们仍然是NSManagedObject。我试图在核心数据实体选项中给出类名以发出请求（核心数据）BAPRequest的对象类，但它一直说我必须子类化NSManagedObject，而子类化NSManagedObject是不可能的：

我做不到：

BAPRequest: NSManagedObject

---

XCode不喜欢它。

看看。这里有一个关于如何使用它的教程：。它会为您省去很多麻烦。

谢谢，但我实际上在尝试学习它，并得到实际的编码答案，这样我就可以申请我目前正在做的许多类似的事情。有时还会尝试使用mogenerator

BAPRequest: NSManagedObject