DbArithmeticExpression arguments must have a numeric common type

The Microsoft Visual Studio 2013 Entity Framework database query does not support the subtraction of two dates to calculate TimeSpan.

For example the following statement will throw a runtime error:

site.VisitFrequencySec < ((TimeSpan)(dtNow - site.LastVisitDate)).TotalSeconds)

To solve the problem create a computed database column to calculate the difference between the dates and use the computed value for comparison.

Column definition:

[SecondsSinceLastVisit]  AS (datediff(second,[LastVisitDate],getdate()))

Now you can use the computed column in the C# Entity Network comparison.

site.VisitFrequencySec < site.SecondsSinceLastVisit