Swift 如何加上「；一对一；“的一部分；“一对多”；获取结果

我希望能够将玩家的数据添加到许多关系的“一对一”部分。提取为我做了一些聚合，但我想知道它属于什么

player

我有一个CoreData模型，如下所示：

func statsPerPlayer(player: Players, managedContext: NSManagedObjectContext)  -> [String: Int] {

    var resultsDic = [String: Int]()

    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Shifts")
    let predicate               = NSPredicate(format: "playersRelationship = %@", player)
    fetchRequest.predicate      = predicate

    let nsExpressionForKeyPath  = NSExpression(forKeyPath: "timeOnIce")

    let nsExpressionForFunctionMin = NSExpression(forFunction: "min:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionMin = NSExpressionDescription()
    nsExpressionDescriptionMin.expression = nsExpressionForFunctionMin
    nsExpressionDescriptionMin.name = "minShift"
    nsExpressionDescriptionMin.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionMax = NSExpression(forFunction: "max:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionMax = NSExpressionDescription()
    nsExpressionDescriptionMax.expression = nsExpressionForFunctionMax
    nsExpressionDescriptionMax.name = "maxShift"
    nsExpressionDescriptionMax.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionSum = NSExpression(forFunction: "sum:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionSum = NSExpressionDescription()
    nsExpressionDescriptionSum.expression = nsExpressionForFunctionSum
    nsExpressionDescriptionSum.name = "sumShift"
    nsExpressionDescriptionSum.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionAvg = NSExpression(forFunction: "average:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionAvg = NSExpressionDescription()
    nsExpressionDescriptionAvg.expression = nsExpressionForFunctionAvg
    nsExpressionDescriptionAvg.name = "avgShift"
    nsExpressionDescriptionAvg.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionCount = NSExpression(forFunction: "count:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionCount = NSExpressionDescription()
    nsExpressionDescriptionCount.expression = nsExpressionForFunctionCount
    nsExpressionDescriptionCount.name = "countShift"
    nsExpressionDescriptionCount.expressionResultType = .integer16AttributeType

    fetchRequest.propertiesToFetch   = [nsExpressionDescriptionMin, nsExpressionDescriptionMax, nsExpressionDescriptionSum, nsExpressionDescriptionAvg, nsExpressionDescriptionCount]

    fetchRequest.resultType = .dictionaryResultType

    do {

        let fetchArray = try managedContext.fetch(fetchRequest)
        print(fetchArray)
        resultsDic = fetchArray.first as! [String : Int]

    } catch let error as NSError {

        print("\(self) -> \(#function): Could not fetch. \(error), \(error.userInfo)")
    }

    return resultsDic

}  //statsPerPlayer

我有一个如下所示的获取请求：

func statsPerPlayer(player: Players, managedContext: NSManagedObjectContext)  -> [String: Int] {

    var resultsDic = [String: Int]()

    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Shifts")
    let predicate               = NSPredicate(format: "playersRelationship = %@", player)
    fetchRequest.predicate      = predicate

    let nsExpressionForKeyPath  = NSExpression(forKeyPath: "timeOnIce")

    let nsExpressionForFunctionMin = NSExpression(forFunction: "min:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionMin = NSExpressionDescription()
    nsExpressionDescriptionMin.expression = nsExpressionForFunctionMin
    nsExpressionDescriptionMin.name = "minShift"
    nsExpressionDescriptionMin.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionMax = NSExpression(forFunction: "max:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionMax = NSExpressionDescription()
    nsExpressionDescriptionMax.expression = nsExpressionForFunctionMax
    nsExpressionDescriptionMax.name = "maxShift"
    nsExpressionDescriptionMax.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionSum = NSExpression(forFunction: "sum:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionSum = NSExpressionDescription()
    nsExpressionDescriptionSum.expression = nsExpressionForFunctionSum
    nsExpressionDescriptionSum.name = "sumShift"
    nsExpressionDescriptionSum.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionAvg = NSExpression(forFunction: "average:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionAvg = NSExpressionDescription()
    nsExpressionDescriptionAvg.expression = nsExpressionForFunctionAvg
    nsExpressionDescriptionAvg.name = "avgShift"
    nsExpressionDescriptionAvg.expressionResultType = .integer16AttributeType

    let nsExpressionForFunctionCount = NSExpression(forFunction: "count:", arguments: [nsExpressionForKeyPath])
    let nsExpressionDescriptionCount = NSExpressionDescription()
    nsExpressionDescriptionCount.expression = nsExpressionForFunctionCount
    nsExpressionDescriptionCount.name = "countShift"
    nsExpressionDescriptionCount.expressionResultType = .integer16AttributeType

    fetchRequest.propertiesToFetch   = [nsExpressionDescriptionMin, nsExpressionDescriptionMax, nsExpressionDescriptionSum, nsExpressionDescriptionAvg, nsExpressionDescriptionCount]

    fetchRequest.resultType = .dictionaryResultType

    do {

        let fetchArray = try managedContext.fetch(fetchRequest)
        print(fetchArray)
        resultsDic = fetchArray.first as! [String : Int]

    } catch let error as NSError {

        print("\(self) -> \(#function): Could not fetch. \(error), \(error.userInfo)")
    }

    return resultsDic

}  //statsPerPlayer

但是，我想包括此数据所针对的

播放器

。如何在结果中添加

一对多

关系的

“到一”

部分

---

谢谢

在上面的代码中，只需将相关关系名称添加到要获取的属性：

fetchRequest.propertiesToFetch   = ["playersRelationship", nsExpressionDescriptionMin, nsExpressionDescriptionMax, nsExpressionDescriptionSum, nsExpressionDescriptionAvg, nsExpressionDescriptionCount]

然后，返回的词典将包括键“playersRelationship”，其值设置为相应

Players

对象的

NSManagedObjectID

。然后，您可以使用上下文的

对象（with:）

方法访问

Players

对象本身

更新

所以经过一些测试，结果是：

a） 如果将关系包含在propertiesToFetch中，则CoreData会对

count

aggregate函数产生混淆。这将导致

无效的密钥路径（请求对仅toOne密钥路径进行聚合操作）

错误

b） 如果在propertiesToFetch中包含关系，则会混淆所有其他聚合函数的CoreData。（它计算每个对象的聚合，而不仅仅是匹配谓词的对象。）

这两个问题的解决方案都是按属性将关系添加为GROUP BY。CoreData随后正确计算聚合，并正确识别

count

为有效操作。因此，添加以下行：

fetchRequest.propertiesToGroupBy   = ["playersRelationship"]

---

如果您只是将“playersRelationship”添加到属性数组estofetch会发生什么？如果我添加

player.playersShiftRelationship如果我添加
shifts.playersRelationship，我会将
无法识别的选择器发送到实例
我收到了相同的错误。您正在获取移位，因此需要在移位实体上指定关系的名称，即“PlayerRelationship”。我想我会按照您的建议执行：
让实体=NSEntityDescription.entity（forEntityName:“移位”，in:managedContext）让移位=移位（entity:entity！，insertInto:managedContext）
我得到了以下错误：
[error]错误：异常处理请求：，无效的keypath（请求在仅toOne的keypath上进行聚合操作）：用户信息为（null）的timeOnIce
@PaulS。我不明白为什么会这样；您能用当前代码和错误编辑您的原始帖子吗(s)。当前代码与发布的代码完全相同，错误也相同。@pbasdf做得很好，谢谢。这可能是我唯一没有尝试的组合。你知道一种快速的方法，可以在我所有的
播放器
中运行上述内容，而不需要另一个
播放器
获取和for in循环吗？只要删除谓词-返回的数组将每个玩家有一本字典。