ios - Swift核心数据NSFetchRequest谓词可获取日期时间

Question

我有一个名为UVHour的数据库表，其结构如下

我的应用程序将通过如下所示的JSON填充UVHour表

[
    {
        "ORDER": 1,
        "DATE_TIME": "SEP/04/2020 04 AM",
        "UV_VALUE": 0
    },
    {
        "ORDER": 2,
        "DATE_TIME": "SEP/04/2020 05 AM",
        "UV_VALUE": 0
    }
]

当前NSFetchRequest

static var uvIndexNowRequest: NSFetchRequest<UVHour>
    {
        let dateTimeNow = Date()
        let formatter = DateFormatter()
        formatter.dateFormat = "MMM/d/yyyy hh a"
        let dateHourStr = formatter.string(from: dateTimeNow)
        
        let request: NSFetchRequest = UVHour.fetchRequest()
        
        request.sortDescriptors = [NSSortDescriptor(key: "order", ascending: true)]

        // Below code will throw 'NSInvalidArgumentException', reason: 'Unable to parse the format string "date_time == Sep/4/2020 08 PM"
        // request.predicate = NSPredicate(format: "date_time == \(dateHourStr)")
        
        return request
    }

问题
如何编写一个谓词，以获取与当前日期和当前时间匹配的UVHour？
示例
假设当前日期是2020年9月4日04:10 AM。
基于上述JSON，我将获取以下的UVHour

[
    {
        "ORDER": 1,
        "DATE_TIME": "SEP/04/2020 04 AM",
        "UV_VALUE": 0
    }
]

我怎样才能做到这一点？

Answer 1

我能够更新 uvIndexNowRequest 来找到我的解决方案。见下面的代码

static var uvIndexNowRequest: NSFetchRequest<UVHour>
    {
        let dateTimeNow = Date()
        
        let formatter = DateFormatter()
        formatter.timeZone = .current
        formatter.dateFormat = "MMM/d/yyyy hh a"
        
        // Find date String from 'formatter.dateFormat'
        let dateHourStr = formatter.string(from: dateTimeNow)
        
        // Get date from dateHourStr
        let someDateTimeOpt = formatter.date(from: dateHourStr)
        
        let request: NSFetchRequest = UVHour.fetchRequest()
        
        request.sortDescriptors = [NSSortDescriptor(key: "order", ascending: true)]
        
        if let someDate = someDateTimeOpt {
            request.predicate = NSPredicate(format: "date_time == %@", someDate as CVarArg)
        }
        
        return request
    }