Nullable object must have a value error in linq SQL C#

The problem occurs because you access the Value property of a Nullable type which is null (or, more precisely, whose HasValue property is false). How to fix this depends on what you want to do:

If you want to filter out items where TourOpID is null, just add a where clause:

(frombinCompleteData
whereb.TourOpID!=null//filter
selectb.TourOpID).Distinct()

If you want to use a replacement value, e.g. 0, if TourOpID is null, use the null coalescing operator ??, which converts your int? into an int:

(frombinCompleteData
selectb.TourOpID??0).Distinct()

or, alternatively,

selectnewComboBoxItemString(){ValueString=a.GetValueOrDefault().ToString()});

If you just want to show a different ComboBox entry if TourOpID is null, use the ternary operator ?::

selectnewComboBoxItemString(){
ValueString=(a==null?"notouroperator":a.Value.ToString())
});

If you want to show the empty string if a is null, the solution is even simpler:

selectnewComboBoxItemString(){ValueString=a.ToString()});

since Nullable.ToString returns an empty string if it does not have a value.

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Ramesh Palaniappan10y ago
Accepted answer
The problem occurs because you access the Value property of a Nullable type which is null (or, more precisely, whose HasValue property is false). How to fix this depends on what you want to do:
If you want to filter out items where TourOpID is null, just add a where clause:
(frombinCompleteData
whereb.TourOpID!=null//filter
selectb.TourOpID).Distinct()
If you want to use a replacement value, e.g. 0, if TourOpID is null, use the null coalescing operator ??, which converts your int? into an int:
(frombinCompleteData
selectb.TourOpID??0).Distinct()
or, alternatively,
selectnewComboBoxItemString(){ValueString=a.GetValueOrDefault().ToString()});
If you just want to show a different ComboBox entry if TourOpID is null, use the ternary operator ?::
selectnewComboBoxItemString(){
ValueString=(a==null?"notouroperator":a.Value.ToString())
});
If you want to show the empty string if a is null, the solution is even simpler:
selectnewComboBoxItemString(){ValueString=a.ToString()});
since Nullable.ToString returns an empty string if it does not have a value.