String.IsNullOrWhiteSpace in LINQ Expression

Question

I have the following code:

return this.ObjectContext.BranchCostDetails.Where(
    b => b.TarrifId == tariffId && b.Diameter == diameter
        || (b.TarrifId==tariffId && !string.IsNullOrWhiteSpace(b.Diameter))
        || (!b.TarrifId.HasValue) && b.Diameter==diameter);

And I get this error when I try to run the code:

LINQ to Entities does not recognize the method 'Boolean IsNullOrWhiteSpace(System.String)' method, and this method cannot be translated into a store expression."

How can I solve this problem and write code better than this?

Answer 1

You need to replace

!string.IsNullOrWhiteSpace(b.Diameter)

with

!(b.Diameter == null || b.Diameter.Trim() == string.Empty)

For Linq to Entities this gets translated into:

DECLARE @p0 VarChar(1000) = ''
...
WHERE NOT (([t0].[Diameter] IS NULL) OR (LTRIM(RTRIM([t0].[Diameter])) = @p0))

and for Linq to SQL almost but not quite the same

DECLARE @p0 NVarChar(1000) = ''
...
WHERE NOT (LTRIM(RTRIM([t0].[TypeName])) = @p0)