Swift - 建立一对多关系

问题描述

假设我们有 2 个实体：

-人物（姓名、年龄、..）

-房子（颜色）

我们用 @interface CutsomStackView : nsstackview @property (nonatomic) NSView *viewA; @property (nonatomic) NSView *viewB; - (id)initWithFrame:(NSRect)frame views:(NSArray<NSView *> *)views; @end @implementation CutsomStackView - (id)initWithFrame:(NSRect)frame views:(NSArray<NSView *> *)views { if (!(self = [super initWithFrame:frame])) return nil; _viewA = views[0]; _viewB = views[1]; self.detachesHiddenViews = YES; self.orientation = NSUserInterfaceLayoutOrientationVertical; self.spacing = 0; self.distribution = nsstackviewdistributionFill; CGFloat viewAHeight = NSHeight(_viewA.frame); [self addArrangedSubview:_viewA]; [self addArrangedSubview:_viewB]; _viewA.translatesAutoresizingMaskIntoConstraints = NO; [_viewA setContentHuggingPriority:NSLayoutPriorityrequired forOrientation:NSLayoutConstraintOrientationVertical]; [_viewA.heightAnchor constraintEqualToConstant:topBarViewHeight].active = YES; _viewB.translatesAutoresizingMaskIntoConstraints = NO; [_viewB setContentHuggingPriority:NSLayoutPriorityDefaultLow forOrientation:NSLayoutConstraintOrientationVertical]; return self; } @end 为每个房子多次记录数据

我们想让房子里的所有人都涂成蓝色

我们如何获取这个？

我试过这个代码，但它得到了所有人

house.addToPeople (newPeople)

怎么做？

解决方法

试试这个功能。它的作用是获取所有 People 并创建一个包含所有结果的数组。

func getAllItems() -> [People]? {
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "People")
        request.returnsObjectsAsFaults = false
        
        do {
            let result: NSArray = try context.fetch(request) as NSArray
            return (result as? [People])!
        } catch let error {
            print("Errore recupero informazioni dal context \n \(error)")
        }
        return nil
    }

如果您想按照特定条件（例如颜色）执行搜索，请在 request 后使用以下代码：

//Here i'm searching by index,if you need guidance for your case don't hesitate asking
 request.predicate = NSPredicate(format: "index = %d",currentItem.index) 

编辑：实际上上面的代码只是为了得到所有的人，如果你想根据房屋进行搜索，请执行以下操作：

  func retrieve()-> [People]{
//Fetch all of the houses with a certain name
        let houseRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "House")
        houseRequest.predicate = NSPredicate(format: "name = %@","newName") //This seearch is by name
        houseRequest.returnsObjectsAsFaults = false
        do {
//put the fetched items in an array
            let result: NSArray = try context.fetch(houseRequest) as NSArray
            let houses = result as? [Houses]
//Get the people from the previous array
            let people: [People]? = (houses.people!.allObjects as! [People])
            return people
        } catch let error {
            print("Errore recupero informazioni dal context \n \((error))")
        }
            return nil
        
    }

,

感谢您的回答！

在这个例子中，“houses”是一个数组，所以我们必须添加一个索引 ➔ houses[0].people!.AllObjects

非常感谢您的解释。