如何预取关系 NSManagedObject 的关系

Posted 2023-03-05

【中文标题】如何预取关系 NSManagedObject 的关系

【英文标题】：how to prefetch relationships of a relationship NSManagedObject

【发布时间】：2013-01-08 15:59:41

【问题描述】：

我正在搜索，需要加快速度。我有一系列汽车零件，我想找到有这些零件的汽车。这部分我做得很好。 NSManagedObject Cars.h

（cars 有一个名为 ToCarParts 的 NSSet，它列出了汽车的所有汽车零件）

NSMagagedObject Parts.h （Parts 有一个名为 ToCars 的 NSSet，它列出了与此相关的所有汽车）

//This takes all results gathered by using parts to search for car, and converts them to have the main object be a car
-(NSArray*)convertResultsToCars:(NSArray*)records
    NSMutableArray *manipulator =[NSMutableArray arrayWithArray:records];
    NSMutableArray *convertedArray =[[NSMutableArray alloc]init];

    for (int i=0; i<[manipulator count]; i++) 
        CarPart *FromManipulator=(CarPart*)[manipulator objectAtIndex:i];
        [convertedArray addObjectsFromArray:[[partFromManipulator toCars]allObjects]];
    

    NSLog(@"Results from core data = %i",[convertedArray count]);
    return [NSArray arrayWithArray:convertedArray];

当我从此处获取结果时，问题出现了，稍后必须在应用程序中加载所有 carParts。

Car *carResult =(Cars*)[resultsConvertedToCarsArray objectAtIndex:i];

        partsFromCar =[NSMutableArray arrayWithArray:[[carResult toParts]allObjects]];

如何在我的原始查询中预取上述信息，以便该信息已加载到对象中？

这是我最初的获取请求：

NSEntityDescription *entity = [NSEntityDescription entityForName:@"CarParts" inManagedObjectContext:[self managedObjectContext]];
[fetchRequest setEntity:entity];
    [fetchRequest setPredicate:[self parseCarPartsIntoAPredicate:carPartsArray]];
    [fetchRequest setReturnsDistinctResults:YES];
    //I guess I would use something like this? but how would I structure it?
    [fetchRequest setRelationshipKeyPathsForPrefetching:@"I need to prefetch the toParts nsset of the cars found here (although in reality it brings up every instance of that car part, which I then have to convert into a car... something like found a car part, car for that part is a buick, what are the parts of the buick? ok, preload those parts"];

提前谢谢你！

【参考方案1】：

NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Post"];
[fetchRequest setRelationshipKeyPathsForPrefetching:@[@"Picture"]];

【参考方案2】：

创建了一个 nsmanagedobject 来保存这些对象...