Question

Let’s say I have a custom class like this one:

public class Customer    
{        
 public int CustomerID { get; set; }        
 public string CompanyName { get; set; }        
 public string BusinessAddress { get; set; }        
 public string Phone { get; set; } 
 public int ParentID { get; set; } 
}

I create custom objects from the database using a datareader. Ex:

  while (dr.Read())
  {
    listCustomers.Add(new Customer(
          Convert.ToInt32(dr["CustomerID"]),
          Convert.ToString(dr["CompanyName"]),
          Convert.ToString(dr["BusinessAddress"]),
          Convert.ToString(dr["Phone"]),
          Convert.ToInt32(dr["ParentID"]),
)

ParentID can be null in the database (and I can’t change it). When it’s null, the conversion obviously fails.

How should I handle null values retrieved from the DB to populate my business objects? Would it be good pratice to use Nullable Types in my custom class? Any other tips?

Answer 1

Absolutely. Nullable types are perfectly fine. Otherwise, you’d have to come up with some stupid convention a-la “when ParentID is -1, this means that Customer has no parent”. Nullable types enforce this “by design”: if there’s no parent, ParentID will be null.

As for hydrating your objects, consider using ORM tools (such as NHibernate or BLToolkit), since you don’t really want to spend 50% of your development tine writing SQL queries and populating your objects from a data reader