CoreData数据库操作关联操作

 let des = NSEntityDescription.entity(forEntityName: "Student", in: self.getContext())
        let student = NSManagedObject(entity: des!,insertInto: self.getContext())
        student.setValue("张杰", forKey: "name")
        student.setValue(12, forKey: "idCard")
        
        let teDes = NSEntityDescription.entity(forEntityName: "Teacher", in: self.getContext())
        let teacher = NSManagedObject(entity: teDes!,insertInto: self.getContext())
        teacher.setValue("老王", forKey: "name")
        teacher.setValue(32, forKey: "age")
        
        let des1 = NSEntityDescription.entity(forEntityName: "Student", in: self.getContext())
        let student1 = NSManagedObject(entity: des1!,insertInto: self.getContext())
        student1.setValue("谢娜", forKey: "name")
        student1.setValue(12, forKey: "idCard")
        
        let teDes1 = NSEntityDescription.entity(forEntityName: "Teacher", in: self.getContext())
        let teacher1 = NSManagedObject(entity: teDes1!,insertInto: self.getContext())
        teacher1.setValue("老王1", forKey: "name")
        teacher1.setValue(32, forKey: "age")
        
        var set = Set<NSManagedObject>()
        set.insert(student)
        set.insert(student1)
        teacher.setValue(set, forKey: "students")
        
        var stSet = Set<NSManagedObject>()
        stSet.insert(teacher)
        stSet.insert(teacher1)
        student.setValue(stSet, forKey: "teachers")
        
        try! self.getContext().save()
        print(NSTemporaryDirectory())
        
        //查找teacher的学生都叫什么
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Teacher");
        //查找
        let pre = NSPredicate(format: "name = '老王'", argumentArray: nil)
        request.predicate = pre
        
        //执行查找
        let arr = try! self.getContext().fetch(request) as![NSManagedObject]
        for item in arr { //获取到每一个老师
            let set = item.value(forKey: "students") as! Set<NSManagedObject>
            for stu in set {
                let name=stu.value(forKey: "name")as! String
                print("老王的学生为名\(name)")
            }
            //删除
            //self.getContext().delete(item)
        }
        try! self.getContext().save()
    }
    func getContext() -> NSManagedObjectContext {
        let delegate=UIApplication.shared.delegate as! AppDelegate
        let context=delegate.persistentContainer.viewContext
        return context