What should I use to compare DBNull ? Using DBNull.Value or ToString().IsNullOrEmpty()

问题

I can check for a DBnull on a data row using any of the methods.

Either by using

if(dr[0][0]==DBNull.Value)
//do somethin

or by doing

if(dr[0][0].ToString().IsNullOrEmpty())
//do something

In Both Cases I will be getting same result.

But Which one is conecptually right approach. Which was will use less resources

回答1:

The first way is somewhat correct. However, more accepted way is:

if ( dr[0][0] is DBNull )

And the second way is definitely incorrect. If you use the second way, you will get true in two cases:

1. Your value is DBNull
2. Your value is an empty string

回答2:

Conceptually the comparison to DBNull.Value is the correct one.

You can also use :

if (Convert.IsDBNull(dr[0]))
{
}

You could also use, which I'm not a fan of, purely because it's a type comparison rather than a value comparison:

if (dr[0] is DBNull)
{
}

回答3:

Is always use :

dr[0].IsNull(0) 

Assuming that the creators of this function know the best way/most efficient way of comparing..

回答4:

The simplest way

if (dr[0][0] == DBNull.Value)
//do somethin

is perfectly valid and readable.

Even though == compares references, it works here because DBNUll.Value is the only instance of DBNull class - so all DBNull values are actually this exact reference.

来源：https://stackoverflow.com/questions/3393958/what-should-i-use-to-compare-dbnull-using-dbnull-value-or-tostring-isnullore