How does one reliably check if a nullable property contains no data? DBNull is killing me

Question

I've begun using Massive, by Rob Conery. Awesome little "ORM" and very performant. However, I'm running into issues with System.DBNull comparisons on my nullable fields.

For example, I want to check if a property matches another property (in this example, a long type)

if (obj.MemberId == otherObj.MemberId) return true;

throws exception: Operator '==' cannot be applied to operands of type 'System.DBNull' and 'long'. In this case, obj.MemberId was null (more specifically, DBNull).

Ok, so I check if it's DBNull.Value first right? Like this:

if (obj.MemberId != DBNull.Value)
    return obj.MemberId == otherObj.MemberId;

Cool, that works, at least while obj.MemberId is DBNull, but when it's not (contains a long), another exception: Operator '!=' cannot be applied to operands of type 'long' and 'System.DBNull'.

DBNull is killing me. How does one reliably check if a nullable property contains no data?

What about if (obj.MemberId.Equals(otherObj.MemberId)) return true; ? — Larry, Apr 09 '11 at 18:53

score 6 · Accepted Answer · answered Apr 09 '11 at 13:18

6

Did you tried by using is operator?

if (obj.MemberId is DBNull)
{
    // it is null
    return false;
}
else
{
    // has some value
    return obj.MemberId == otherObj.MemberId;
}

answered Apr 09 '11 at 13:18

Waqas Raja

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Nope, lemme try it now... brb. – Chaddeus Apr 09 '11 at 13:20
+1, but I'd suggest taking both objects into account in your `DBNull` test: `if (obj.MemberId is DBNull || otherObj.MemberId is DBNull)`. Unless, of course, you want to consider two `DBNulls` as being equal, in which case it gets more complicated. – Frédéric Hamidi Apr 09 '11 at 13:24
@Chad, (@Frederic Hamidi) is right you also need to consider whether `otherObj is DBNull`, to avoid any exceptions that can occur. – Waqas Raja Apr 09 '11 at 13:27
Thank you Frederic for the heads up, in this case only one side is DBNull'able, but I'll keep that in mind. – Chaddeus Apr 09 '11 at 13:29
@Chad, you're welcome, and be careful to always compare the objects in the right order then ;) – Frédéric Hamidi Apr 09 '11 at 13:32

score 1 · Answer 2 · answered Apr 09 '11 at 13:41

1

Just using Convert.IsDBNull should do.

http://msdn.microsoft.com/en-us/library/system.convert.isdbnull(v=VS.90).aspx

answered Apr 09 '11 at 13:41

tia

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score 0 · Answer 3 · answered Dec 12 '14 at 22:13

0

try this. this works for me;

string test = DBNull.Value.Equals(obj.Qty) ? string.Empty : obj.Qty.ToString();

answered Dec 12 '14 at 22:13

Muru Bakthavachalam

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score 0 · Answer 4 · answered Apr 09 '11 at 13:18

0

if (!DBNull.Value.Equals(obj.MemberID) && obj.MemberID !=null && obj !=null)

or

if (!DBNull.Value.Equals(obj) && obj.MemberID !=null && obj !=null)

Select whatever applies to your case. This will give you a full proof check.

answered Apr 09 '11 at 13:18

Marshal

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How does one reliably check if a nullable property contains no data? DBNull is killing me

4 Answers4