Check for DbNull in C#

Question

I am finding difficulties in validating the following

if(personDS.person[0].IdFk!= DBNull.Value)

this is the compile time error - cannot be applied to operands of type 'System.Guid and 'System.Dbnull'

Exception is thrown when you try to access IdFk because it's not nullable. — Alex Dn
– Alex Dn, Commented Jan 19, 2012 at 9:26
You might find the answer here: stackoverflow.com/questions/211436/nullable-guid Nullable GUID question. — Carlos Quintanilla
– Carlos Quintanilla, Commented Jan 19, 2012 at 9:29

Alex Dn · Accepted Answer · 2012-01-19 09:23:12Z

4

I think you should check:

if(personDS.person[0].IsIdFkNull())

answered Jan 19, 2012 at 9:23

Alex Dn

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Comments

Jason · Accepted Answer · 2012-01-19 09:26:53Z

0

You can also check against an empty Guid

if (personDS.person[0].IdFk == Guid.Empty )

answered Jan 19, 2012 at 9:26

Jason

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Akshita · Accepted Answer · 2012-01-19 09:27:02Z

0

try

if(!(personDS.person[0].IdFk is System.DBNull))

answered Jan 19, 2012 at 9:27

Akshita

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1 Comment

Alex Dn Over a year ago

If IdFk is null, it will throw exception. Check DataSet autogenerated class for implementation. The property throws and exception. Maybe it's can be changed by column property, but it's not worked for me.

Ɖiamond ǤeezeƦ · Accepted Answer · 2012-01-19 09:31:10Z

0

Id is a Guid, which is a Value type and will therefore never equal DBNull.Value. Before I can fully help, I will need to know the types of personDS (DataSet maybe?) and person (DataTable maybe). Assuming so, then maybe:

if (!personDS.person[0].IsNull("IdFK"))

If person is not a DataTable but a class then check for either IdFk == Guid.Empty, if IdFk is a Guid, or IdFk == null if IdFk is Guid?.

answered Jan 19, 2012 at 9:31

Ɖiamond ǤeezeƦ

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Comments

Giorgio Minardi · Accepted Answer · 2012-01-19 10:00:23Z

0

Is IdFk declared as nullable ? Es:

public Guid? Idfk

If so you can :

if(personDS.person[0].IdFk.HasValue)

edited Jan 19, 2012 at 10:00

answered Jan 19, 2012 at 9:33

Giorgio Minardi

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2 Comments

Nuffin Over a year ago

As far as I can tell this is complete nonsense, for the followingg reasons: 1) public starts with a lower p 2) the ? suffix has to be appended to the type, not the identifier 3) if personDS.person[0].IdFK indeed is null the code will throw an InvalidOperationException, else the condition will always be false, since DBNull.Value doesn't equal anything but itself and a Guid can never be of type DBNull (and it won't compile, since you can't compare Guid and DBNull without casting either one to object, which will do a reference comparison)

Giorgio Minardi Over a year ago

True, I without VS now and coding in vb this period. Made a some confusion :) Edited the response anyway, thanks.

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