如何在linq中比较可为空的变量？

Question

I try to select some data by linq but system shows me this error

Expression of type 'System.DateTime' cannot be used for parameter of type 'System.Object' of method 'Boolean Equals(System.Object)'

My WorkingResults.EffectiveDate is DateTime? but my date variable is DateTime. How do I change my code to fix this out?

  WorkingResult workingResultObj = (from workingResult in this.DataWorkspace.ApplicationData.WorkingResults
where workingResult.EmployeeCode == employeeCode  && workingResult.EffectiveDate.Equals(date)                                         
select workingResult).FirstOrDefault();

Thank you for any help.

Answer 1

Well, there are a couple of workarounds. First, you could make it a DateTime:

workingResult.EffectiveDate.GetValueOrDefault(DateTime.MinValue).Equals(date)

I don't know what a valid date is. Or, you could use Object.Equals:

Object.Equals(workingResult.EffectiveDate, date)

Which may not give you the intended results. If you always know effective date has a value, then you can use @spajce approach.

Answer 2

You can use .HasValue and Its must like

...
where workingResult.EmployeeCode == employeeCode && 
(workingResult.EffectiveDate.HasValue && 
 workingResult.EffectiveDate.Value.Date == date.Date).FirstOrDefault();

Answer 3

 WorkingResult workingResultObj = 
  (
      from workingResult 
      in this.DataWorkspace.ApplicationData.WorkingResults
      where 
            workingResult.EffectiveDate.HasValue
            && workingResult.EmployeeCode == employeeCode  
            && workingResult.EffectiveDate.Value == date                                         
      select workingResult
  ).FirstOrDefault();