Question

I have a method which should return a list of anonymous objects with a calculated column like this:

        var tomorrow = DateTime.Today.AddDays(1);
        return from t in this.Events
                where (t.StartTime >= DateTime.Today && t.StartTime < tomorrow && t.EndTime.HasValue)
                select new
                {
                    Client = t.Activity.Project.Customer.Name,
                    Project = t.Activity.Project.Name,
                    Task = t.Activity.Task.Name,
                    Rate = t.Activity.Rate.Name,
                    StartTime = t.StartTime,
                    EndTime = t.EndTime.Value,
                    Hours = (System.Data.Objects.SqlClient.SqlFunctions.DateDiff("m", t.StartTime, t.EndTime.Value) / 60),
                    Description = t.Activity.Description
                };

Unfortunately I get the following error from the DateDiff function:

The specified method ‘System.Nullable1[System.Int32] DateDiff(System.String, System.Nullable1[System.DateTime], System.Nullable`1[System.DateTime])’ on the type ‘System.Data.Objects.SqlClient.SqlFunctions’ cannot be translated into a LINQ to Entities store expression.

Any ideas what I could have done wrong here?

EDIT: I also tried the EntityFunctions class mentioned here, but that did not work as well.

Minutes = EntityFunctions.DiffMinutes(t.EndTime, t.StartTime),

Answer 1

[Edit]

Hours = (System.Data.Objects.SqlClient.SqlFunctions.DateDiff("mi", t.StartTime, t.EndTime.Value) / 60)

is not supported SQL CE.

Hours = ((TimeSpan)(t.EndTime.Value - t.StartTime)).TotalHours

Throws an DbArithmeticExpression Exception

So, I think you’ll have to do it in two steps. Grab the data you need, then calculate the time difference in memory.

var events = (from t in context.Events
    where (t.StartTime >= DateTime.Today && t.StartTime < tomorrow && t.EndTime.HasValue)
    select t).ToArray();

return from t in events
    select new
    {
         ...
         Hours = (t.EndTime.Value - t.StartTime).TotalHours
    };