SQL Data Reader - handling Null column values

c# sqldatareader

I'm using a SQLdatareader to build POCOs from a database. The code works except when it encounters a null value in the database. For example, if the FirstName column in the database contains a null value, an exception is thrown.

employee.FirstName = sqlreader.GetString(indexFirstName);

What is the best way to handle null values in this situation?

You need to check for IsDBNull:

if(!SqlReader.IsDBNull(indexFirstName))
{
  employee.FirstName = sqlreader.GetString(indexFirstName);
}

That's your only reliable way to detect and handle this situation.

I wrapped those things into extension methods and tend to return a default value if the column is indeed null:

public static string SafeGetString(this SqlDataReader reader, int colIndex)
{
   if(!reader.IsDBNull(colIndex))
       return reader.GetString(colIndex);
   return string.Empty;
}

Now you can call it like this:

employee.FirstName = SqlReader.SafeGetString(indexFirstName);

and you'll never have to worry about an exception or a null value again.

You should use the as operator combined with the ?? operator for default values. Value types will need to be read as nullable and given a default.

employee.FirstName = sqlreader[indexFirstName] as string;
employee.Age = sqlreader[indexAge] as int? ?? default(int);

The as operator handles the casting including the check for DBNull.

employee.FirstName = sqlreader[indexFirstName] as string;

For integers, if you cast to a nullable int, you can use GetValueOrDefault()

employee.Age = (sqlreader[indexAge] as int?).GetValueOrDefault();

or the null-coalescing operator (??).

employee.Age = (sqlreader[indexAge] as int?) ?? 0;

SQL Data Reader - handling Null column values

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