Question

func fetchRequestFromViewContext(nameOfEntity: NSManagedObject) {
    let fetchRequest = NSFetchRequest<nameOfEntity>(entityName: "\(nameOfEntity)")
    do {
        let result = try? CoreDataStack.instance.viewContext.fetch(fetchRequest)

    }
}

尝试抽象核心数据获取请求，从而创建一个类型为托管对象的参数，并将其传递给fetch请求泛型但是没有让我，我是否在正确的轨道上抽象出这个核心数据获取请求？

Answer 1

NSFetchRequest(entityName:)需要String，但nameofEntity为NSManagedObject。将其更改为String，然后传入实体的类型。您可以使用泛型（下面的<T>）来允许符合NSManagedObject的任何类。

func fetchRequestFromViewContext<T: NSManagedObject>(nameOfEntity: String, type: T.Type) {
    let fetchRequest = NSFetchRequest<T>(entityName: nameOfEntity)
    do {
        let result = try? CoreDataStack.instance.viewContext.fetch(fetchRequest)

    }
}

要打电话给你，你只需要这样做：

fetchRequestFromViewContext(nameOfEntity: "YourEntity", type: YourEntity.self)

Answer 2

static func fetch<T>(entity: T.Type, withPredicate predicate: NSPredicate? = 
nil) -> Array<T>? where T : NSFetchRequestResult {

let request: NSFetchRequest<T> = NSFetchRequest<T>(entityName: 
String(describing: T.self))
    request.predicate = predicate
    do {
        return try context.fetch(request)
    }catch{
        print(error.localizedDescription)
    }
    return nil
}

摘要核心数据获取请求

2 个答案: