Setting ASP.net MVC model class int, string & DateTime value to dbnull

Question

Hey all I am trying to assign a DBNull to an int class value as shown below:

namespace ETTData.Models
{
    public class CHeld
    {
        public class AdNo {
            public int RequestID { get; set; } = DBNull.Value;

            public string TLead { get; set; } = DBNull.Value;

            public DateTime RequestDate { get; set; } = DBNull.Value;
        }
    }
}

However, I get the error(s) of:

Error CS0029 Cannot implicitly convert type 'System.DBNull' to 'int' ETTData

Error CS0029 Cannot implicitly convert type 'System.DBNull' to 'string' ETTData

Error CS0037 Cannot convert null to 'DateTime' because it is a non-nullable value type

This also seems to be an issue when doing a DateTime and string varibles?

What would I be missing in order to get this to work?

Why are you trying to assign a *database specific* type to your C# objects? Why is `null` not an option here? — DigiFriend, May 10 '17 at 13:06
@DigiFriend I've read that **NULL** and **DBNull** are different from each other and if you are using varibles that are to be saved in a database then you need to use **DBNull** and not **NULL**. http://stackoverflow.com/questions/4958379/what-is-the-difference-between-null-and-system-dbnull-value — StealthRT, May 10 '17 at 13:09
Yes, but *only* when you are saving to the DB. You can't assign `DBNull` to C# objects, as you have seen. — DigiFriend, May 10 '17 at 13:10
I'd keep the C# properties as null. Then default the parameters to null in your DB procs that can be null and omit them from the SQL command parameter list if they equal null. — Wheels73, May 10 '17 at 13:11
What if there is no value, say for RequestID, and therefore it never sets it to anything if i dont have **= something** in the variable definition? — StealthRT, May 10 '17 at 13:11
Well, try it and see if it works, cuz this approach isn't working at the moment. Are you using an ORM? — Mark C., May 10 '17 at 13:11

Drew Aguirre · Answer 1 · 2017-05-10T13:25:08.457

1

Hi why are you trying to put db null value to your model class?

if you wan't your properties to receive null values you can use ? to make your types to nullable.

 public int? RequestID { get; set; }
 public string TLead { get; set; }
 public DateTime? RequestDate { get; set; }

Hope this helps.

edited May 10 '17 at 13:25

answered May 10 '17 at 13:13

Drew Aguirre

375
2
15

2

Quick, remove the ? on string! – Matt May 10 '17 at 13:15
There is no `string?` as `string` is always nullable – Mats391 May 10 '17 at 13:15
Yup Eagle Eyes :-D. Thanks! – Drew Aguirre May 10 '17 at 13:25
@Mats391 yup your right. there is no ? for string types bcoz it is always nullable.. – Drew Aguirre May 10 '17 at 13:29

score 1 · Answer 2 · answered May 10 '17 at 13:14

You can only use DBNull with types that accept it as a valid value - the built in types do not - nor does any type you can create yourself - class/struct cannot be derived from DBNull - it is sealed, so can't be inherited from.

You need to use null for properties that can be nullable in the DB (and model struct types that cannot be null, such as int as nullables - int?).

When saving to the DB, check if these are null and if so, pass in DBNull to your database.

Setting ASP.net MVC model class int, string & DateTime value to dbnull

2 Answers2