how does one compare the date part of a nullable datetime in a linq / lambda query?

Question

I have something like the following: ``` new ObservableCollection(SomeDataCollection.Where(a => a.AGD_Category.Equals((int)AGD_CategoryEnum.Med) && ((a.AGG_DateStart.Date <= SelectedUntill) && (a.AGG_DateEnd.Value.Date >= SelectedFrom)))); ``` now my a.AGG_DateEnd is a nullable datetime and whenever there is a null value in the list I get an exception because of the "a.AGG_DateEnd.Value.Date" part. But the thing is, the a.AGG_DateEnd also contains hours and minutes, but I do not want this causes my comparison to give unreliable results. What can I do to improve? Thank you,

Accepted Answer

A quick hack is: ``` a.AGG_DateEnd.GetValueOrDefault().Date >= SelectedFrom ``` This is OK because the `default(DateTime)` (which equals its own `.Date`) is not greater than any (other) `DateTime` value. Otherwise the usual thing to do is: ``` a.AGG_DateEnd.HasValue && a.AGG_DateEnd.Value.Date >= SelectedFrom ``` where the double `&` ensures short-cut evaluation. Addition after comments: If you want the opposite answer in the case where it is `null`, it is: ``` (a.AGG_DateEnd ?? DateTime.MaxValue).Date >= SelectedFrom ``` respectively: ``` !a.AGG_DateEnd.HasValue || a.AGG_DateEnd.Value.Date >= SelectedFrom ``` Later edit: Since C# 6.0 (July 2015), you can use the `?.` operator instead. So use the shorter code: ``` a.AGG_DateEnd?.Date >= SelectedFrom ``` which will (formally, at least) compare two nullable values of type `DateTime?`. When either operand is "null" (i.e. `.HasValue` gives `false`), such a comparison gives `false`. If you want the opposite bool result in case of null, that is: ``` !(a.AGG_DateEnd?.Date < SelectedFrom) ``` Observe how `x >= y` is different from `!(x < y)` when we use these lifted operators that operate on `Nullable<>` values. Any lifted operator (like `>=` or `<`) will return `false` immediately if one of `x` and `y` is null; only if both `x` and `y` are non-null, will they be unwrapped and the contents compared with the non-lifted operator whose return value will be used.

how does one compare the date part of a nullable datetime in a linq / lambda query?

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