Using func while retriving date from database

debugcn Published at Dev

Wojciech Szabowicz

I have a method that retrieves timestamp intervals from db and it looks like this:

public IEnumerable<DateTime> GetCurrentsFlagTimestampPoints(DateTime startDate, DateTime endDate)
{
    return currentsRepository.GetTimestampPoints(startDate, endDate).Select(timestamp => new DateTime(timestamp.Year, timestamp.Month, timestamp.Day)).Distinct();
}

But now I want to use it more in a more generic way, so i want to pass Func<> that will describe resulting date format so once I want to return

new DateTime(timestamp.Year, timestamp.Month, timestamp.Day)

and once

new DateTime(timestamp.Year, timestamp.Month, timestamp.Day, timestamp.Hour)

I could do that using overloads of some sort but that would change the already existing structure of some methods.

I don't know how to tackle this, is it possible??

Edit:

It works nice without Expression so:

    public IEnumerable<DateTime> GetCurrentsFlagTimestampPoints(DateTime startDate, DateTime endDate, Func<DateTime, DateTime> dateTimeExpr)
    {
        return currentsRepository.GetTimestampPoints(startDate, endDate).Select(dateTimeExpr).Distinct();
    }

Amir Popovich

You need to pass a Expression<Func<DateTime,DateTime>> as a param:

public IEnumerable<DateTime> GetCurrentsFlagTimestampPoints(DateTime startDate, DateTime endDate, Expression<Func<DateTime, DateTime>> dateTimeExpr)
{
    return currentsRepository.GetTimestampPoints(startDate, endDate).Select(dateTimeExpr).Distinct();
}

Expression<Func<DateTime, Datetime>> f1 = timestamp => new DateTime(timestamp.Year, timestamp.Month, timestamp.Day);

Expression<Func<DateTime, Datetime>> f1 = timestamp => new DateTime(timestamp.Year, timestamp.Month, timestamp.Day, timestamp.Hour);

GetCurrentsFlagTimestampPoints(DateTime.Now, DateTime.Now, f1); // or f2

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