Question

I am trying to take a DateTime value, and if it is not null return the Short Time String. My query looks like this:
(TimeIn is NOT NULLABLE, whereas TimeOut is NULLABLE)

    var times = from t in db.TimePostings
                where t.MemberID == member.MemberID
                select new
                {
                    Date = t.TimeIn.ToShortDateString(),
                    TimeIn = t.TimeIn.ToShortTimeString(),
                    TimeOut = t.TimeOut.HasValue ? t.TimeOut.Value.ToShortTimeString() : "-------"
                };
gvTimePostings.DataSource = times;
gvTimePostings.DataBind();

but this fails when I try to databind with the error:

Could not translate expression ‘Table(TimePosting).Where(t =>
(t.MemberID == Invoke(value(System.Func1[System.String])))).Select(t
=> new <>f__AnonymousType84(Date = t.TimeIn.ToShortDateString(), TimeIn = t.TimeIn.ToShortTimeString(), TimeOut =
IIF(t.TimeOut.HasValue, (t.TimeOut ??
Invoke(value(System.Func`1[System.DateTime]))).ToShortTimeString(),
“——-“), Hours = “”))’ into SQL and could not treat it as a local
expression.

I also get a similar error if I try to use:

TimeOut = t.TimeOut.HasValue ? Convert.ToDateTime(t.TimeOut).ToShortTimeString() : "-------"

however, if I change the TimeOut property to:

TimeOut = t.TimeOut.HasValue ? t.TimeOut.ToString() : "-------",

it works fine, but does not format the time like I want it (shortTimeString).

what’s up with that?

Answer 1

As others have said, the problem is with trying to convert ToShortDateString etc to SQL. Fortunately, this is easy to fix: fetch the data with SQL, then format it in .NET:

var timesFromDb = from t in db.TimePostings
                  where t.MemberID == member.MemberID
                  select new { t.TimeIn, t.TimeOut };

var times = from t in timesFromDb.AsEnumerable()
            select new
            {
                Date = t.TimeIn.ToShortDateString(),
                TimeIn = t.TimeIn.ToShortTimeString(),
                TimeOut = t.TimeOut.HasValue 
                                     ? t.TimeOut.Value.ToShortTimeString() 
                                     : "-------"
            };

The call to AsEnumerable() here basically means, “stop trying to process the query using SQL; do the rest in LINQ to Objects”.