How to safely cast nullable result from sqlreader to int?

Question

I have a table which contains null values and I need to get data from the table using SqlDataReader. I can't figure out how I can safely cast DBNull to int.

I'm doing it in this way at the moment:

...
reader = command.ExecuteReader();
while (reader.Read()) {
     int y = (reader["PublicationYear"] != null) ? Convert.ToInt32(reader["PublicationYear"]) : 0;
     ...
}
...

but getting a Object cannot be cast from DBNull to other types. when PublicationYear is null.

How can I get the value safely?

Thanks.

Answer 1

You should compare reader["PublicationYear"] to DBNull.Value, not null.

Answer 2

DBNull is not the same as null. You should try something like this instead:

int y = (reader["PublicationYear"] != DBNull.Value) ? ...

Answer 3

int ord = reader.GetOrdinal("PublicationYear");
int y = reader.IsDBNull(ord) ? 0 : reader.GetInt32(ord);

Or, alternatively:

object obj = reader["PublicationYear"];
int y = Convert.IsDBNull(obj) ? 0 : (int)obj;

Answer 4

You should explicitly check if the value returned is of type DBNull

while (reader.Read()) {
     int y = (!reader["PublicationYear"] is DBNull) ? Convert.ToInt32(reader["PublicationYear"]) : 0;
     ...
}

In fact, you can do this comparison by value as well as type:

reader["PublicationYear"] != DBNull.Value

In short - you can expect DBNull to be returned for nulls from the database, rather than null itself.

Answer 5

as an alternative you can do the following. as you are converting DBNull to 0, alter the procedure that does the select. so that the select itself returns zero for a null value.

snippet to demonstrate the idea

    SELECT ...
           ,ISNULL (PublicationYear, 0) as PublicationYear
           ...
    FROM sometable

advantage of this is that, no additional checking is needed in your code.

Answer 6

Change

reader["PublicationYear"] != null

to

reader["PublicationYear"] != DBNull.Value

Answer 7

That's the error: (reader["PublicationYear"] != null) You should test for DBNull.Value....

Answer 8

Change your test from (reader["PublicationYear"] != null) to (reader["PublicationYear"] != DBNull.Value).

Answer 9

Database null values should be compared with DBNull.Value

reader = command.ExecuteReader(); while (reader.Read()) { int y = (reader["PublicationYear"] != DBNull.Value) ? Convert.ToInt32(reader["PublicationYear"]) : 0; ... }