swift - 如何检查CoreData存在

Question

我试图检查该项目是否退出coredata，如果不将其添加到coredata。我如何实施检查？

var authorList = [AuthorList]()

let articleEntity = NSEntityDescription.entityForName("AuthorList", inManagedObjectContext: self.context!)
let newAuthor = AuthorList(entity: articleEntity!, insertIntoManagedObjectContext: self.context!)

   //if authorID is not in coredata then....
     newAuthor.authorName = authorName!
     newAuthor.authorImage = authorImage!
     newAuthor.newspaperName = newspaperName!
     newAuthor.newsPaperImage = newsPaperImage!
     newAuthor.authorID = authorID!

Answer 1

使用NSPredicate来过滤coredata中的articlID ......

let fetchRequest = NSFetchRequest(entityName: "FavArticles")
let predicate = NSPredicate(format: "articleID == %ld", articleID!)
fetchRequest.predicate = predicate
let fetchResults = self.context!.executeFetchRequest(fetchRequest, error: nil) as? [FavArticles]
if fetchResults!.count > 0 {
  println("already favd")
}

Answer 2

如果任何机构正在寻找swift 3解决方案：

斯威夫特3

Xcode 8x

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="topnavbar" class="topNavBar">
<!--Logo and some contents here -->
</div>

Answer 3

func checkIfItemExist(id: String) -> Bool {
        let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Products")
        fetchRequest.fetchLimit =  1
        fetchRequest.predicate = NSPredicate(format: "productId == %@" ,id)
        do {
            let count = try DatabaseHelper.context!.count(for: fetchRequest)
            if count > 0 {
                return true
            }else {
                return false
            }
        }catch let error as NSError {
            print("Could not fetch. \(error), \(error.userInfo)")
            return false
        }
    }