weibo/Weibo/UserData.swift

//
//  UserData.swift
//  Weibo
//
//  Created by Qihua Pan on 2020/8/18.
//  Copyright © 2020 Qihua Pan. All rights reserved.
//

import Foundation
import CoreData
class UserData{
   static func getUser()->User{
        let fetchRequest: NSFetchRequest = User.fetchRequest()
        let context=getContext()
         do {
                let result = try context.fetch(fetchRequest)
            print("count=\(result.count)")
                if result.count>0{
                    return result[0]
                }else{
                    let user=NSEntityDescription.insertNewObject(forEntityName: "User", into: context) as! User
                    saveContext()
                    return user
                }
         } catch {
             fatalError();
         }
    }
    
    
    static func clearAll(){
        let context=getContext()
        let fetchRequest: NSFetchRequest = User.fetchRequest()
           do {
            let result = try context.fetch(fetchRequest)
            for item in result{
                context.delete(item)
            }
            saveContext()
        } catch {
            fatalError();
        }
    }
    
    static func saveContext () {
        let context=getContext()
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }
    
    static func getContext()->NSManagedObjectContext{
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        print("context=\(context)")
        return context
    }
}