Operator '&&' cannot be applied operands to bool and bool?

Sample query

var users = (from t in T_Table
join x in X_Table on t.id equals x.id
where t.pid == x.pid
&& somelist.contains(t.id) //UNABLE TO APPLY somelist?.contains
select (new User(){name = t.user})).ToList();


I'm unable null check somelist.

It shows:

Operator '&&' cannot be applied operands to bool and bool?

somelist

4 Answers
4

problem here is if you write like this

somelist?.contains(t.id) return null in case somelist is null and null is not boolean value.

somelist?.contains(t.id)

null

So you should try like this

&& (somelist!=null ? somelist.contains(t.id) : false)


Check : 3 misuses of ?. operator in C# 6

Your error occurs becasue

bool b1 = true;
bool? b2 = true;
bool result = b1 && b2; //b2 could also be null


There are two ways to solve this.

1

bool result = b1 && b2 == true; // somelist?.contains() == true


2

make sure your item can't be null before you run your query (this also works for linq2SQL) so you don't need a null-conditional operator in your query

if(somelist == null)
{
somelist = new List<yourType>();
}


check if somelist is not null first before accessing contains.

var users = (from t in T_Table
join x in X_Table on t.id equals x.id
where t.pid == x.pid
&& somelist != null && somelist.contains(t.id) //UNABLE TO APPLY somelist?.contains
select (new User(){name = t.user})).ToList();


First check whether somelist is having any data or not, if somelist is null you can't operate contains on somelist

or

Where(u => somelist.Contains(t.Id.Value))


should also work if somelist is not null

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