c# - DbArithmeticExpression arguments must have a numeric common type

Question

TimeSpan time24 = new TimeSpan(24, 0, 0);
TimeSpan time18 = new TimeSpan(18, 0, 0);    

// first get today's sleeping hours
List<Model.Sleep> sleeps = context.Sleeps.Where(
    o => (clientDateTime - o.ClientDateTimeStamp < time24) && 
          o.ClientDateTimeStamp.TimeOfDay > time18 && 
          clientDateTime.TimeOfDay < time18 && 
          o.UserID == userid).ToList(); 

This Linq expression throws this exception:

DbArithmeticExpression arguments must have a numeric common type.

Please Help!

Answer 1

Arithmetic with DateTime is not supported in Entity Framework 6 and earlier. You have to use DbFunctions*. So, for the first part of your statement, something like:

var sleeps = context.Sleeps(o =>
    DbFunctions.DiffHours(o.ClientDateTimeStamp, clientDateTime) < 24);

Note that the DiffHours method accepts Nullable<DateTime>.

Entity Framwork core (when used with Sql Server, maybe other db providers) supports the DateTime AddXxx functions (like AddHours). They're translated into DATEADD in SQL.

_{*EntityFunctions prior to Entity Framework version 6.}