CoreData篇(三)-CoreData的增删改查

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本篇来介绍一下Core Data的增删改查.

增

这里,增就直接使用AppDelegate里头生成的persistentContainer的viewContext了.以及saveContext方法.

	1.取出NSManagedObjectContext.
	AppDelegate *delegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
    NSManagedObjectContext *context = delegate.persistentContainer.viewContext;
    2.通过上下文,新建一个CoreData Entity模型.
    Employee *employee = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:context];
    3.进行属性设置
    employee.name = @"张立强";
    employee.age = 48;
    employee.sex = @"女";
    4.保存上下文
    [delegate saveContext];

如果不保存上下文的话.那么存储就是失效的

查

为何先说查,毕竟查出来了才好删嘛(PS.直接删除数据库文件的当我没说哈).

/// 2.查
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Employee"];
    /// 查询条件
//    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"age = 30"];
    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"name == '张立强1'"];
    fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES]];
    NSArray <Employee *> *array = [context executeFetchRequest:fetchRequest error:nil];
    for (Employee *employee in array) {
        NSLog(@"employee age : %hd" ,employee.age);
    }
    

改

一般要改点什么,都是先查出来再改.改的话,走一遍增的后半部分逻辑就行.(千万别忘了保存)

/// ------比如我已经查出来employee了
employee.name = @"abc";
employee.age = 12;

[delegate saveContext];

删

我们就在查的基础上讲删吧.

for (Employee *employee in array) {
        NSLog(@"employee age : %hd" ,employee.age);
        [context deleteObject:employee];
    }
    [delegate saveContext];

使用context的 deleteObject:方法可以轻松的删除一个实体对象.
最后,别忘了保存改动.