problem with null column

Question

One column in my database (of type double) has some null values. I am executing a sored procedure to get the data in my app

 wipDBTableAdapters.XLSFacturiTableAdapter TAFacturi = new wipDBTableAdapters.XLSFacturiTableAdapter();
               var dtfacturi = TAFacturi.GetData(CodProiect);

Then i try to do something like this:

if (dtfacturi[i].CANTITATE == null)
   {
    //do something
   }

this is giving a warning :

The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double?

However when i run my code i get the following exception:

StrongTypingException
The value for column 'CANTITATE' in table 'XLSFacturi' is DBNull. 

How am I supposed to resolve this ?

Answer 1

DBNull is not null

Check DBNull documentation on MSDN

Try this test :

if (DBNull.Value.Equals(dtfacturi[i].CANTITATE))
{
    //do something
}

Answer 2

While working with data in DB and need to check NULL values use DBNull class instead of .NET null.

Answer 3

Database NULLs are different from null, you should use IsDBNull to check for database NULLs.

Edit: Mixed up VB.Net with C#

Compare with DBNull.Value rather than the VB specific IsDBNull.

Answer 4

Try this:

if (dtfacturi[i].CANTITATE == DBNull.Value)
{
  //do something
}

Answer 5

A value of type 'double' is indeed never null; if you want to export into an array of doubles, you need to have two columns in the database, one containing the data and one containing a flag as to whether the data is valid or not.

This is really a bug in your database-to-array adapter code; I can't find any google hits for XLSFacturiTableAdapter so I'm not sure who to shout at.

Answer 6

When using TypedDataSets, check if coloumn is null this way..

   if (dtfacturi[i].IsCANTITATENull()) 
   { 
       //do something 
   } 

Also note that, C# null is different than Database null. Type of your coloumn is double which is a value type that can never be null. In order to check if your coloumn value is null you need to compare it with DBNull.Value.