I get this error: System.ArgumentNullException: Value cannot be null. But that is the point right? if .FreeAmount is null it should check in the AmountList for a Selected amount. However it fails doing so. I can't really see what I have done wrong here.
var amount = string.IsNullOrEmpty(formModel.FreeAmount)
? formModel.AmountList
.Where(x => x.Selected)
.Select(a => a.Value)
.SingleOrDefault()
: formModel.FreeAmount;
You will only get a System.ArgumentNullException in the code you posted if both FreeAmount and AmountList are null. If there is some other default value you want to use in this case, you could do something like:
var amount = string.IsNullOrEmpty(formModel.FreeAmount)
? formModel.AmountList == null
? "Default value if FreeAmount and AmountList are null"
: formModel.AmountList
.Where(x => x.Selected)
.Select(a => a.Value)
.SingleOrDefault()
: formModel.FreeAmount;
Otherwise, if you just want it to return null in this case (which I suppose is more likely, since that's currently a possibility with SingleOrDefault) then you can just use the null-conditional operator (?.):
var amount = string.IsNullOrEmpty(formModel.FreeAmount)
? formModel.AmountList? // <-- The '?' will return null if AmountList is null
.Where(x => x.Selected)
.Select(a => a.Value)
.SingleOrDefault()
: formModel.FreeAmount;
In the above statement,
Left had side of the ternary operator can result in NULL if formModel is NULL,
So, string.IsNullOrEmpty(formModel.FreeAmount) => will result in TRUE.
So, the ternary operator will evaluate left side (true) of the : symbol which is,
formModel.AmountList
.Where(x => x.Selected)
.Select(a => a.Value)
.SingleOrDefault()
This will result in System.ArgumentNullException because formModel value is null.
So, in the case of formModel being NULL the command will fail with System.ArgumentNullException.
formModel is null then formModel.FreeAmount will throw a NullReferenceException. It will never execute string.IsNullOrEmpty nor get to the ternary operator.formModel.FreeAmount was instead formModel?.FreeAmount - but even so the ternary would still throw a NullReferenceException.
formModel's class as welll asAmountList's class.fromModelwas null then you would getNullReferenceException, notArgumentNullException.formModel.AmountList.Where(x => x.Selected).DefaultIfEmpty(0).Select(a => a.Value).SingleOrDefault()