如何从Swift中的核心数据访问子数据和父数据

guard let context = persistentContainer.viewContext else { return }

let fetchRequest: NSFetchRequest<ParentEntity> = ParentEntity.fetchRequest()
let parentEntity = try context.fetch(fetchRequest).first

if let children = parentEntity?.children {
    for child in children {
        // 处理每个子实体
    }
}

if let parent = childEntity.parent {
    // 处理父实体
}

try context.save()

// 假设有两个实体ParentEntity和ChildEntity，它们之间有一对多的关系

// 获取ManagedObjectContext
guard let context = persistentContainer.viewContext else { return }

// 创建父实体并保存
let parentEntity = ParentEntity(context: context)
try context.save()

// 创建子实体并设置其父实体关系
let childEntity = ChildEntity(context: context)
childEntity.parent = parentEntity

// 保存子实体
try context.save()

// 访问父实体的子实体
if let children = parentEntity.children {
    for child in children {
        print("Child name: \(child.name ?? "")")
    }
}

// 访问子实体的父实体
if let parent = childEntity.parent {
    print("Parent name: \(parent.name ?? "")")
}