如何属性保存与其他实体具有一对多关系的更新管理对象？

Question

如果我的核心数据中有三个实体，它们之间都具有一对多关系：

extension Progress {

    @nonobjc public class func createFetchRequest() -> NSFetchRequest<Progress> {
        return NSFetchRequest<Progress>(entityName: "Progress")
    }

    @NSManaged public var goal: Goal
    @NSManaged public var metric: Set<Metric>

}

extension Metric {

    @nonobjc public class func createFetchRequest() -> NSFetchRequest<Metric> {
        return NSFetchRequest<Metric>(entityName: "Metric")
    }
    
    @NSManaged public var value: NSDecimalNumber
    @NSManaged public var metricToGoal: Goal
    @NSManaged public var progress: Progress

}

extension Goal {

    @nonobjc public class func createFetchRequest() -> NSFetchRequest<Goal> {
        return NSFetchRequest<Goal>(entityName: "Goal")
    }

    @NSManaged public var title: String
    @NSManaged public var progress: Set<Progress>
    @NSManaged public var goalToMetric: Set<Metric>
}

如果获取其中一个实体并更新它：

let metricRequest = Metric.createFetchRequest()
metricRequest.predicate = NSPredicate(format: "value == %@", metric.value)
if let fetchedMetric = try? self.context.fetch(metricRequest) {
   // update Metric
}

我是否还必须获取其余两个实体并将新更新的实体附加到它们？

if let fetchedGoal = try? self.context.fetch(goalRequest) {
   fetchedGoal.goalToMetric.append(updatedMetric)
}

if let fetchedProgress = try? self.context.fetch(goalProgress) {
   fetchedProgress.metric.append(updatedMetric)
}

或者 Core Data 是否足够智能，我只需要为更新的实体保存上下文，它会处理剩下的事情？

Answer 1

Do I have to fetch the rest two entities as well and append the newly updated entity to them?

没有。您可以阅读有关关系数据库如何工作的更多信息，here。

单个 Metric 对象对应于 CoreData-backed 数据库中专用 table 中的单个记录。如果更新 value 的 Metric - 不需要更新关系。在 one-to-many 关系的情况下，数据库中的每个 Metric 记录将仅存储 Goal 和 Progress 的 ObjectID。 Goal 和 Progress 记录都不会存储与它们相关的指标的任何信息。

如何属性保存与其他实体具有一对多关系的更新管理对象？

How to property save the updated managed object that has one-to-many relationships with other entities?

ios

swift

core-data

nsmanagedobject