C# ?? null coalescing operator

Question

I have defined Class Person property Birthday as nullable DateTime? , so why shouldn’t the null coalescing operator work in the following example?

cmd.Parameters.Add(new SqlParameter("@Birthday",
   SqlDbType.SmallDateTime)).Value =       
     person.Birthday ?? DBNull.Value;

The compiler err I got was "Operator '??' cannot be applied to operands of type 'System.DateTime?' and 'System.DBNull'"

The following also got a compile error :

cmd.Parameters.Add(new SqlParameter("@Birthday", 
  SqlDbType.SmallDateTime)).Value = 
   (person.Birthday == null) ? person.Birthday:DBNull.Value;

I added a cast to (object) as recommended by Refactor, and it compiled, but didn’t work properly and the value was stored in the sqlserver db as null in both cases.

SqlDbType.SmallDateTime)).Value =       
         person.Birthday ?? (object)DBNull.Value;

Can someone explain what is going on here?

I needed to use the following clumsy code:

   if (person.Birthday == null) 
    cmd.Parameters.Add("@Birthday", SqlDbType.SmallDateTime).Value 
      = DBNull.Value;
     else cmd.Parameters.Add("@Birthday", SqlDbType.SmallDateTime).Value = 
          person.Birthday;

Got this from the other post: SqlDbType.SmallDateTime)).Value = person.Birthday ?? (object)DBNull.Value; Thanks! — Lill Lansey
– Lill Lansey, Commented Aug 6, 2010 at 16:18

Dave D · Accepted Answer · 2010-08-06 15:27:06Z

23

The problem is that DateTime? and DBNull.Value are not the same type so you can't use the null coalescing operator on them.

In your case you can do person.Birthday ?? (object)DBNull.Value to pass a value of type object through to Add()

answered Aug 6, 2010 at 15:27

Dave D

9,2104 gold badges36 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

JYelton · Accepted Answer · 2013-12-19 18:19:48Z

5

I prefer to iterate over my parameters just before executing the query, changing all instances of null to DBNull as appropriate, for example:

foreach (IDataParameter param in cmd.Parameters)
    if (param.Value == null)
        param.Value = DBNull.Value;

This lets me leave null values as-is and simply swap them out en masse later.

edited Dec 19, 2013 at 18:19

answered Aug 6, 2010 at 16:16

JYelton

36.6k28 gold badges140 silver badges196 bronze badges

1 Comment

Andrew Over a year ago

My issue with this is the extra overhead of iterating over the parameters after the fact, versus handling them immediately.

James Curran · Accepted Answer · 2010-08-06 15:29:12Z

3

Your first problem is that for the ?? or ?: operator, the objects for either choice must be the same type. Here they are different type.

answered Aug 6, 2010 at 15:29

James Curran

104k37 gold badges186 silver badges264 bronze badges

1 Comment

Allen Rice Over a year ago

So what does ?: do? edit: nevermind, I knew that, just never saw those 2 symbols put together like that before. msdn.microsoft.com/en-us/library/ty67wk28.aspx

Collectives™ on Stack Overflow

C# ?? null coalescing operator

3 Answers 3

Comments

1 Comment

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

1 Comment

Linked

Related