Core data 数据库入门及提升

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/* 增 */
- (void)addAction {
 
 Test *obj = [NSEntityDescription insertNewObjectForEntityForName:@"Test" inManagedObjectContext:self.app_delegate.managedObjectContext];
 UserInfoModel *model = [[UserInfoModel alloc]init];{
 model.age = arc4random_uniform(100);
 model.sex = arc4random_uniform(2);
 model.address = @"江苏省南京市江宁区将军大道十字路口";
 }
 
 obj.score = @(arc4random_uniform(100));
 obj.username = @"将军大道";
 obj.userinfo = model;
 
 [self.app_delegate saveContext]; //! < 持久化到本地
 
}

/* 删 */
- (void)deleteAction{
 
 NSFetchRequest *req = [[NSFetchRequest alloc]initWithEntityName:@"Test"];
 
 NSArray *objs = [self.app_delegate.managedObjectContext executeFetchRequest:req error:nil];
 
 if (objs.count == 0) {
 NSLog(@"删除失败 --> 无数据");
 return;
 }
 
 Test *obj = [objs objectAtIndex:arc4random_uniform((u_int32_t)objs.count)];
 
 [self.app_delegate.managedObjectContext deleteObject:obj]; //! < 删除对象
 
 NSLog(@"删除成功");
 
 [self.app_delegate saveContext]; //! < 持久化到本地
 
}

/* 改 */
- (void)changeAction{
 NSFetchRequest *req = [[NSFetchRequest alloc]initWithEntityName:@"Test"];
 
 NSArray *objs = [self.app_delegate.managedObjectContext executeFetchRequest:req error:nil];
 
 if (objs.count == 0) {
 NSLog(@"修改失败 ---> 无数据");
 return;
 }
 
 Test *obj = [objs objectAtIndex:arc4random_uniform((u_int32_t)objs.count)];
 
 obj.username = @"修改数据"; //! < 拿到数据对象后直接赋值操作并保存即可
 UserInfoModel *mod = [obj.userinfo copy];
 mod.address = @"南京市鼓楼区鼓楼地铁站🚇";
 obj.userinfo = mod;
 NSLog(@"修改成功");
 
 [self.app_delegate saveContext]; //! < 持久化到本地
 
}

/* 查 */
- (void)getAction{
#warning 对于模型中的数据, NSFetchRequest 并不能对模型中属性值实现过滤操作,但是可以对模型外的数据进行处理
 NSFetchRequest *req = [NSFetchRequest fetchRequestWithEntityName:@"Test"];
 
 NSSortDescriptor *desc = [NSSortDescriptor sortDescriptorWithKey:@"score" ascending:NO]; //! < 实现查找的数据降序排列(NO,YES 为升序)
 
 
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"score < %ld", 60]; //! < 将分数小于60的查找出来
 
 req.predicate = predicate;
 
 /*

 // 分页用到 查找的数量与偏移量
 req.fetchLimit = 5; //! < 数量 | 结论:无论查找的数量设置多少,NSFetchRequest
 // | ---> 都会遍历所有数据,并且按照事先约定的条件进行
 req.fetchOffset = req.fetchLimit * (curPage - 1); //! < 偏移量 | 处理后输出


 NSLog(@"**********************第%ld页*************************",curPage);

 */
 req.sortDescriptors = @[desc];
 
 NSArray *array = [self.app_delegate.managedObjectContext executeFetchRequest:req error:nil];
 
#pragma 模型内的数据可以采用数组的条件过滤操作,然而当进行此步骤操作时,分页效果将完全乱了
 
 NSPredicate *array_predicate = [NSPredicate predicateWithFormat:@"userinfo.age < %ld",20];
 
 array = [array filteredArrayUsingPredicate:array_predicate];
 
 if (array.count == 0) {
 NSLog(@"**********************无数据*************************");
 return;
 }
 
 
 curPage ++;
 
 for (Test *obj in array) {
 UserInfoModel *model = obj.userinfo;
 NSLog(@"%@ | %02ld | %02ld | %@ | %@",obj.username,model.age,[obj.score integerValue],model.sex?@"男":@"女",model.address);
 }
 
}

数据持久的变量初始化

 if (_managedObjectContext != nil) {
 return _managedObjectContext;
 }
 
 NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
 if (!coordinator) {
 return nil;
 }
 _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
 [_managedObjectContext setPersistentStoreCoordinator:coordinator]; //这里需要指定协作器,就是连接对象上下文和模型的桥梁 
 return _managedObjectContext;
 

if (_managedObjectModel != nil) {
 return _managedObjectModel;
 }
 NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"文件名" withExtension:@"momd"]; //这里的`文件名`就是在资源文件中生成的`***.xcdatamodeld `文件名,后缀在 url 中必须为 momd,(其实是个文件夹里面的文件,可以输出地址查看)
 _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL]; //指定模型地址
 return _managedObjectModel;

 if (_persistentStoreCoordinator != nil) {
 return _persistentStoreCoordinator;
 }
 _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
 NSURL *applicationDocumentsDirectory = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
 NSURL *storeURL = [applicationDocumentsDirectory URLByAppendingPathComponent:@"文件名.sqlite"]; //这里是指定数据库存储的地方和名字-->文件名
[_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:nil]; //添加数据库的路径
return _persistentStoreCoordinator;

(必须)如果使用了动态存储,则模型需要遵守/实现 NSCoding 协议

- (void)encodeWithCoder:(NSCoder *)aCoder{
 
 [aCoder encodeObject:[NSNumber numberWithInteger:self.age] forKey:@"age"];
 [aCoder encodeObject:[NSNumber numberWithBool:self.sex] forKey:@"sex"];
 [aCoder encodeObject:self.address forKey:@"address"];
}
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder{
 self = [super init];
 
 if (self) {
 self.age = [[aDecoder decodeObjectForKey:@"age"] integerValue];
 self.sex = [[aDecoder decodeObjectForKey:@"sex"] boolValue];
 self.address = [aDecoder decodeObjectForKey:@"address"];
 }
 
 return self;
}

(可选)如果想通过 copy 来完整拷贝一个模型数据到一个新的模型,则模型需要遵守/实现 NSCopying 协议

- (id)copyWithZone:(nullable NSZone *)zone{
 UserInfoModel *model = [[UserInfoModel allocWithZone:zone]init];
 model.address = self.address;
 
 model.sex = self.sex;
 
 model.age = self.age;
 
 return model;
}