DateTime问题

Question

I could swear this was working two days ago, now it throws an exception...

I am checking against some data in a DataTable . I'm basically counting how many times a certain eventID is found within the last 15 minutes. Here's that code:

int startevents = trackingData
    .Select("RHEventID = 3 AND RHDateEvent > #" + now + "#" ).Length;

I'm defining the 'now' variable just before that - looks like this:

DateTime now = DateTime.Now.AddMinutes(-15);

However this throws a String was not recognized as a valid DateTime exception. Here is an example of the data in the datatable, in the column for RHDateEvent:

2017-02-14 13:58:27 PM (edit - yes this is only one date, not two, in the column)

So what am I doing wrong? Do I need to be converting this DateTime somehow?

Answer 1

I'd really recommend to use Linq-To-DataTable instead of the old and limited Select method:

DateTime in15minutes = DateTime.Now.AddMinutes(15);
var matchingRows = from row in trackingData.AsEnumerable()
                   where row.Field<int>("RHEventID) == 3
                     &&  row.Field<DateTime>("RHDateEvent") > in15minutes
                   select row;

if you now just need the count use:

int matchingRowCount = matchingRows.Count();

This is more readable, powerful and supports compile time safety.

---

If your column is a not a DateTime - but a string -column you need to parse it:

...
&&  DateTime.Parse(row.Field<string>("RHDateEvent"), CultureInfo.InvariantCulture) > in15minutes

Answer 2

It looks like the date time is duplicated...

2017-02-14 13:58:27 PM 2017-02-14 13:57:27 PM

instead of

2017-02-14 13:58:27 PM

Answer 3

如果是实体使用的限制

var startevents = trackingData.Where(e => e.RHEventId = 3 && e.RHDateEvent >= DateTime.Now.AddMinutes(-15)).Count();