Problems with converting NULL to 0

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Hi there.

Help me please with the following problem. I have a DataRow r, filled with data from my database. Now I want to fill an MVC model

C#

public class Customer
{
    private int id;
    private string name;
    private string region;
    private int phone;

    public int Id {get, set}
    public string Name {get, set}
    public string Region {get, set}
    public int Phone {get, set}
}

as shown below

C#

var c = new Customer {
   Id = Convert.ToInt32(r[0]),
   Name = r[1].ToString(),
   Region = r[2].ToString(),
   Phone = Convert.ToInt32(r[3])
   }

The problem is that r[3] corresponds to optional data, and if there is NULL in my database, an error with Convert occurs. What can I use to make Phone to be just 0 in the case when r[3] is NULL ?

Posted 2-Nov-14 12:51pm

brombenzol123

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NeverJustHere · Accepted Answer · 2014-11-02T13:33:00

Solution 2

The problem with storing it in your class as value of 0 is that if you save it back to the database, you will possibly overwrite the NULL value with 0.

A better option is to use the Nullable<int> data type, which allows representation of a missing value, or the phone number.

Also, phone numbers are better stored as strings. They are more complex than just a number. Some have important leading 0's, some may be international, some may be bigger than what an integer can represent.

Posted 2-Nov-14 13:33pm

NeverJustHere

Comments

brombenzol123 3-Nov-14 2:35am

I exchanged int with string and think that was really bad idea to use int for cells containitg nulls. Thank you for useful advices.

NeverJustHere 3-Nov-14 2:40am

There is nothing wrong with using int for data that can be null.

The difference is the string type natively supports null, int does not. The string type is a little unusual in .net in this regard.

The int type can be wrapped around a null manager by using nullable<int>. This would be the correct way of representing any number that may not exist, rather than converting them all to strings.

brombenzol123 3-Nov-14 2:53am

As far as I understand I have to put a sign ? to int's in my model definition as below. But unfortunately it still gives InvalidCastException. Maybe I have to modify my Cast method somehow?

public class Customer
{
private int id;
private string name;
private string region;
private int? phone;

public int Id {get, set}
public string Name {get, set}
public string Region {get, set}
public int? Phone {get, set}
}

NeverJustHere 3-Nov-14 3:05am

Unfortunately, there is no automatic conversion from database values to Nullable int, so you need to code this yourself.

Use something like (from memory, so may need fixing):
NullableInt = dbField.IsNull ? Nothing : dbField.GetInt()

brombenzol123 3-Nov-14 5:32am

I understand. Thanks for helping.

Anthony Mushrow · Accepted Answer · 2014-11-02T13:01:00

Solution 1

You should be able to use Convert.IsDBNull

var c = new Customer {
        Id = Convert.ToInt32(r[0]),
        Name = r[1].ToString(),
        Region = r[2].ToString(),
        Phone = Convert.IsDBNull(r[3]) ? 0 : Convert.ToInt32(r[3])
        }

Posted 2-Nov-14 13:01pm

Anthony Mushrow

Comments

brombenzol123 3-Nov-14 2:37am

I decided to exchange int with string so the problem automatically disappears. But thank you for advice, that's can be useful in future.