Most efficient/aesthetic 3 way boolean check in C#

Question

I have a C# function that is updating a database and need to check to make sure two values in a datarow are not null. I know that ValueA has a value more often than ValueB, so I have a check as follows to make sure I have the most efficient execution (note, using IsNull as a function to check both C# nulls and DBNull.Value):

var value= DataRow["ValueA"];
        if (IsNull(value))
        {
            value= DataRow["ValueB"];
            if (IsNull(value))
            {
                _log.LogError("Error occured while attempting to update a table...");
                return;
            }
        }

Can anyone see a more efficient way to test whether both are null? Is there any way to reduce the number of lines of code but maintain the efficiency?

score 4 · Answer 1 · answered Feb 05 '20 at 15:24

Ultimately you are making 2 null checks, regardless of the order you do them or how pretty your code is. When this is interpreted into IL the compiler will simplify this anyway, but in terms of humanly readable code this is fine. An alternative might be to not malloc value to two different values and null check the values directly like:

if(IsNull(DataRow["ValueA"]) || IsNull(DataRow["ValueB"])
{
    _log.LogError("Error occured while attempting to update a table...");
    return;
}

Diado · Answer 2 · 2020-02-05T16:42:36.767

3

If you are using C# 7 or above you can use the null coalescing operator, like so:

var value = DataRow["ValueA"] ?? DataRow["ValueB"] ?? throw new Exception("Error occured while attempting to update a table...");

Combined with a Try...Catch to catch the exception.

If the values involved are in fact DBNull rather than actual null, then you could do this instead (assuming they're int?s):

var value = DataRow["ValueA"] as int? ?? DataRow["ValueB"] as int? ?? throw new Exception("Error occured while attempting to update a table...");

edited Feb 05 '20 at 16:42

answered Feb 05 '20 at 15:22

Diado

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Nice, didn't know about the null coalescing operator. – Felipe Gutierrez Feb 05 '20 at 15:32
The "throw new Exception" seems to be an invalid expression. I'm getting an error after the 2nd null operator and the compiler complains about unreachable code directly after the expression. – Kemilio Feb 05 '20 at 15:45
What version of C# are you using? Using throws on the right-hand side of the null coalescing operator like that was introduced in C# 7. – Diado Feb 05 '20 at 16:20
`DataRow["ValueA"]` is probably not returning `null` but `DBNull.Value`. – Theodor Zoulias Feb 05 '20 at 16:37
Updated to handle DBNull as well – Diado Feb 05 '20 at 16:42
1

@TheodorZoulias correct, hence my "IsNull" function. Sorry, I should have specified that. – Kemilio Feb 05 '20 at 16:43
@Diado Yeah, the version I'm using is probably C# 6. Not sure I'll be able to make use of that particular feature. – Kemilio Feb 05 '20 at 16:49
1

Ah well, I'll leave it here for people using more recent versions :-) – Diado Feb 05 '20 at 16:50

Most efficient/aesthetic 3 way boolean check in C#

2 Answers2