Question

核心数据实体，上面有两个属性：startDay和startDateTime。这两个属性都是NSDate对象。 startDay将其时间组件设置为午夜，startDateTime指定带有时间的日期。 startDay和startDateTime中的“日历日”都相同。

以下是一些对象

(
    {
        startDateTime = "2014-05-27 08:00:00 +0000";
        startDay = "2014-05-27 00:00:00 +0000";
    },
    {
        startDateTime = "2014-05-27 13:00:00 +0000";
        startDay = "2014-05-28 00:00:00 +0000";
    }
)

需要按startDay分组对象。需要知道“早晨”或“下午”是否有活动。

以下是按startDay分组的结果，并报告了最早和最新的每日活动。

- (void)fetchEventDays
{
    NSExpression *startDateTimeExpression = [NSExpression expressionForKeyPath:@"startDateTime"];
    NSExpression *minStartDateTime = [NSExpression expressionForFunction:@"min:" arguments:[NSArray arrayWithObject:startDateTimeExpression]];
    NSExpression *maxStartDateTime = [NSExpression expressionForFunction:@"max:" arguments:[NSArray arrayWithObject:startDateTimeExpression]];

    NSExpressionDescription *minStartDateTimeExpression = [[NSExpressionDescription alloc] init];
    minStartDateTimeExpression.name = @"minEventStartTime";
    minStartDateTimeExpression.expression = minStartDateTime;
    minStartDateTimeExpression.expressionResultType = NSDateAttributeType;

    NSExpressionDescription *maxStartDateTimeExpression = [[NSExpressionDescription alloc] init];
    maxStartDateTimeExpression.name = @"maxEventStartTime";
    maxStartDateTimeExpression.expression = maxStartDateTime;
    maxStartDateTimeExpression.expressionResultType = NSDateAttributeType;

    NSManagedObjectContext *context = [RKObjectManager sharedManager].managedObjectStore.mainQueueManagedObjectContext;
    NSEntityDescription* entity = [NSEntityDescription entityForName:@"NIModelScheduleData" inManagedObjectContext:context];
    NSAttributeDescription* startDayDesc = [entity.attributesByName objectForKey:@"startDay"];

    NSFetchRequest* fetch = [[NSFetchRequest alloc] init];
    fetch.entity = entity;
    fetch.propertiesToFetch = [NSArray arrayWithObjects:startDayDesc, minStartDateTimeExpression, maxStartDateTimeExpression, nil];
    fetch.propertiesToGroupBy = [NSArray arrayWithObject:startDayDesc];
    fetch.resultType = NSDictionaryResultType;

    NSError *error = nil;
    NSArray *results = [context executeFetchRequest:fetch error:&error];

    NSLog(@"%@", results);
}

该代码正在返回

(
    {
        maxEventStartTime = "2014-05-27 13:00:00 +0000";
        minEventStartTime = "2014-05-27 08:00:00 +0000";
        startDay = "2014-05-27 00:00:00 +0000";
    },
    {
        maxEventStartTime = "2014-05-28 10:00:00 +0000";
        minEventStartTime = "2014-05-28 09:00:00 +0000";
        startDay = "2014-05-28 00:00:00 +0000";
    }
)

如果它看起来像这样会更酷......

(
    {
        eveningEvent = YES;
        morningEvent = YES;
        startDay = "2014-05-27 00:00:00 +0000";
    },
    {
        eveningEvent = NO;
        morningEvent = YES;
        startDay = "2014-05-28 00:00:00 +0000";
    }
)

如何修改我的获取请求以将日期比较转换为NSExpression（或NSExpressionDescription？），以便核心数据检查min/maxEventStartTime是否在中午之前/之后，以及返回BOOL而不是实际的NSDate对象。

集合函数中的核心数据比较

0 个答案: