swift CoreData 的使用

添加增 和查询

//
//  ViewController.swift
//  CodeDtaMM
//
//  Created by ray on 2021/2/14.
//

import CoreData
import UIKit



class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        if var model = self.getNewObj(mType: User.self) {
            model.name = "Test123"
            self.saveCoreDate(model: &model)
        }
        
        
        if let list = self.fetchCoreData(mType: User.self) {
            for item in list {
                print("item  \(item.name)")
            }
        }
        
        
    }
    
    
    func getNewObj<T:NSManagedObject>(mType:T.Type)->T? {
        let appDel = UIApplication.shared.delegate as! AppDelegate

           //获取管理的上下文

        let context = appDel.persistentContainer.viewContext

           //创建一个实例并给属性赋值
        let name = "\(mType.self)"
        let model = NSEntityDescription.insertNewObject(forEntityName: name, into: context) as? T
        return model
    }
    
    //添加数据

    func saveCoreDate<T:NSManagedObject>( model:inout T){
           //加载AppDelegate

        let appDel = UIApplication.shared.delegate as! AppDelegate

           //获取管理的上下文

        let context = appDel.persistentContainer.viewContext

           
          //保存数据

          do {
              try context.save()

              print("保存成功")

           }catch let error{
               print("context can't save!, Error:\(error)")

           }

    }
    
    

    
    func fetchCoreData<T:NSManagedObject>(mType:T.Type)->[T]?{
           //加载AppDelegate

        let appDel = UIApplication.shared.delegate as! AppDelegate

           //获取管理的上下文

        let context = appDel.persistentContainer.viewContext

           // 声明数据请求实体

        if let fetchRequest:NSFetchRequest<T> = mType.fetchRequest() as? NSFetchRequest<T> {
            
            if let peopleList =
                
                try? context.fetch(fetchRequest) {
                return peopleList
            }
            
        }
        
        return nil
          

   //        let predicate = NSPredicate(format:"id=1")  //设置查询条件按照id查找不设置查询条件，则默认全部查找

   //        fetchRequest.predicate=predicate

           //执行查询操作

         

//          do {
//              try context.save()
//
//              print("保存成功")
//
//           }catch let error{
//               print("context can't save!, Error:\(error)")
//
//           }

           

       }

}

创建实体类的时候，不要勾选target