Hello

Could you please help for a simple boolean expression

If a is not equal to Null

I tried

If (a != null) Then

This expression does not work

I look at Help but can not find out

Could you please help

Thanks
S.Hoa

> Could you please help for a simple boolean expression
> If a is not equal to Null
> I tried
> If (a != null) Then


From my point of view it seems that you are trying
to check whether object exists.

Try:
If Not (a Is Nothing) Then

--
Pozdrav,
Josip Medved, MCSD
http://www.jmedved.com

What sort of "Null" are you looking for?
Database Null?
Object is Nothing?
a <> 0&?

"HS1" <(E-Mail Removed)> wrote in message
news:1098135675.785296@ftpsrv1...
> Hello
>
> Could you please help for a simple boolean expression
>
> If a is not equal to Null
>
> I tried
>
> If (a != null) Then
>
> This expression does not work
>
> I look at Help but can not find out
>
> Could you please help
>
> Thanks
> S.Hoa
>
>

Thank you
a is a value of a field in a table of a database. I have to check it is null
or not
I have a solution

If Not (a is DBNull.Value) Then

"Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> What sort of "Null" are you looking for?
> Database Null?
> Object is Nothing?
> a <> 0&?
>
> "HS1" <(E-Mail Removed)> wrote in message
> news:1098135675.785296@ftpsrv1...
> > Hello
> >
> > Could you please help for a simple boolean expression
> >
> > If a is not equal to Null
> >
> > I tried
> >
> > If (a != null) Then
> >
> > This expression does not work
> >
> > I look at Help but can not find out
> >
> > Could you please help
> >
> > Thanks
> > S.Hoa
> >
> >
>
>

you got it, mostly.
i'm not certain if the IS keyword will give you the proper results or not.
this is not a value comparison, but an Object Reference comparison.
it would be safer to use:
If Not (a = DBNull.Value) Then

or use the alternate test using
If Not IsDBNull(a) Then

Gerald

"HS1" <(E-Mail Removed)> wrote in message
news:1098141920.570486@ftpsrv1...
> Thank you
> a is a value of a field in a table of a database. I have to check it is
null
> or not
> I have a solution
>
> If Not (a is DBNull.Value) Then
>
> "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > What sort of "Null" are you looking for?
> > Database Null?
> > Object is Nothing?
> > a <> 0&?
> >
> > "HS1" <(E-Mail Removed)> wrote in message
> > news:1098135675.785296@ftpsrv1...
> > > Hello
> > >
> > > Could you please help for a simple boolean expression
> > >
> > > If a is not equal to Null
> > >
> > > I tried
> > >
> > > If (a != null) Then
> > >
> > > This expression does not work
> > >
> > > I look at Help but can not find out
> > >
> > > Could you please help
> > >
> > > Thanks
> > > S.Hoa
> > >
> > >
> >
> >
>
>

Thank you

I tried to use =, the compiler get the error

Operator '=' is not defined for types 'System.Object' and 'System.DBNull'.
Use 'Is' operator to compare two reference types.
Therefore, I have to change to "Is"
I use VB.Net 2001

Regards
S.Hoa
"Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> you got it, mostly.
> i'm not certain if the IS keyword will give you the proper results or not.
> this is not a value comparison, but an Object Reference comparison.
> it would be safer to use:
> If Not (a = DBNull.Value) Then
>
> or use the alternate test using
> If Not IsDBNull(a) Then
>
> Gerald
>
> "HS1" <(E-Mail Removed)> wrote in message
> news:1098141920.570486@ftpsrv1...
> > Thank you
> > a is a value of a field in a table of a database. I have to check it is
> null
> > or not
> > I have a solution
> >
> > If Not (a is DBNull.Value) Then
> >
> > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed)...
> > > What sort of "Null" are you looking for?
> > > Database Null?
> > > Object is Nothing?
> > > a <> 0&?
> > >
> > > "HS1" <(E-Mail Removed)> wrote in message
> > > news:1098135675.785296@ftpsrv1...
> > > > Hello
> > > >
> > > > Could you please help for a simple boolean expression
> > > >
> > > > If a is not equal to Null
> > > >
> > > > I tried
> > > >
> > > > If (a != null) Then
> > > >
> > > > This expression does not work
> > > >
> > > > I look at Help but can not find out
> > > >
> > > > Could you please help
> > > >
> > > > Thanks
> > > > S.Hoa
> > > >
> > > >
> > >
> > >
> >
> >
>
>

What object type is "a"?
You say a database field, but which object.
Is there an a.value property?

I'm still concerned about using IS here.
Take for example that A is a particular object, and System.DBNull is another
object.
The IS operator is more appropriate to determine if "A" is the same object
as DBNull, not the same value.

Gerald

"HS1" <(E-Mail Removed)> wrote in message
news:1098147081.668852@ftpsrv1...
> Thank you
>
> I tried to use =, the compiler get the error
>
> Operator '=' is not defined for types 'System.Object' and 'System.DBNull'.
> Use 'Is' operator to compare two reference types.
> Therefore, I have to change to "Is"
> I use VB.Net 2001
>
> Regards
> S.Hoa
> "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > you got it, mostly.
> > i'm not certain if the IS keyword will give you the proper results or
not.
> > this is not a value comparison, but an Object Reference comparison.
> > it would be safer to use:
> > If Not (a = DBNull.Value) Then
> >
> > or use the alternate test using
> > If Not IsDBNull(a) Then
> >
> > Gerald
> >
> > "HS1" <(E-Mail Removed)> wrote in message
> > news:1098141920.570486@ftpsrv1...
> > > Thank you
> > > a is a value of a field in a table of a database. I have to check it
is
> > null
> > > or not
> > > I have a solution
> > >
> > > If Not (a is DBNull.Value) Then
> > >
> > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
message
> > > news:(E-Mail Removed)...
> > > > What sort of "Null" are you looking for?
> > > > Database Null?
> > > > Object is Nothing?
> > > > a <> 0&?
> > > >
> > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > news:1098135675.785296@ftpsrv1...
> > > > > Hello
> > > > >
> > > > > Could you please help for a simple boolean expression
> > > > >
> > > > > If a is not equal to Null
> > > > >
> > > > > I tried
> > > > >
> > > > > If (a != null) Then
> > > > >
> > > > > This expression does not work
> > > > >
> > > > > I look at Help but can not find out
> > > > >
> > > > > Could you please help
> > > > >
> > > > > Thanks
> > > > > S.Hoa
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Here is my code

If (DataGrid1.Item(DataGrid1.CurrentCell.RowNumber, 5) Is DBNull.Value) Then

In this code, dataGrid1 presents data for a table. I check the value
(textual type) of current row at column 5 to see that it is Null or not.


"Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> What object type is "a"?
> You say a database field, but which object.
> Is there an a.value property?
>
> I'm still concerned about using IS here.
> Take for example that A is a particular object, and System.DBNull is
another
> object.
> The IS operator is more appropriate to determine if "A" is the same object
> as DBNull, not the same value.
>
> Gerald
>
> "HS1" <(E-Mail Removed)> wrote in message
> news:1098147081.668852@ftpsrv1...
> > Thank you
> >
> > I tried to use =, the compiler get the error
> >
> > Operator '=' is not defined for types 'System.Object' and
'System.DBNull'.
> > Use 'Is' operator to compare two reference types.
> > Therefore, I have to change to "Is"
> > I use VB.Net 2001
> >
> > Regards
> > S.Hoa
> > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed)...
> > > you got it, mostly.
> > > i'm not certain if the IS keyword will give you the proper results or
> not.
> > > this is not a value comparison, but an Object Reference comparison.
> > > it would be safer to use:
> > > If Not (a = DBNull.Value) Then
> > >
> > > or use the alternate test using
> > > If Not IsDBNull(a) Then
> > >
> > > Gerald
> > >
> > > "HS1" <(E-Mail Removed)> wrote in message
> > > news:1098141920.570486@ftpsrv1...
> > > > Thank you
> > > > a is a value of a field in a table of a database. I have to check it
> is
> > > null
> > > > or not
> > > > I have a solution
> > > >
> > > > If Not (a is DBNull.Value) Then
> > > >
> > > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
> message
> > > > news:(E-Mail Removed)...
> > > > > What sort of "Null" are you looking for?
> > > > > Database Null?
> > > > > Object is Nothing?
> > > > > a <> 0&?
> > > > >
> > > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > > news:1098135675.785296@ftpsrv1...
> > > > > > Hello
> > > > > >
> > > > > > Could you please help for a simple boolean expression
> > > > > >
> > > > > > If a is not equal to Null
> > > > > >
> > > > > > I tried
> > > > > >
> > > > > > If (a != null) Then
> > > > > >
> > > > > > This expression does not work
> > > > > >
> > > > > > I look at Help but can not find out
> > > > > >
> > > > > > Could you please help
> > > > > >
> > > > > > Thanks
> > > > > > S.Hoa
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Ah, I see. Well, if it were me, I would explicitly cast the underlying value
to its appropriate sqltype then check for null. However, I do not know what
kind of underlying data you are dealing with.
You could take the shortcut and use the Convert.IsDBNull which will handle
an expression.
Like so:

If Convert.IsDBNull(DataGrid1.Item(DataGrid1.CurrentCell.RowNumber, 5)) Then

It is possible that the way you are doing it will work fine. But it just
seems dangerous to me.

Gerald

"HS1" <(E-Mail Removed)> wrote in message
news:1098163724.554694@ftpsrv1...
> Here is my code
>
> If (DataGrid1.Item(DataGrid1.CurrentCell.RowNumber, 5) Is DBNull.Value)
Then
>
> In this code, dataGrid1 presents data for a table. I check the value
> (textual type) of current row at column 5 to see that it is Null or not.
>
>
> "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > What object type is "a"?
> > You say a database field, but which object.
> > Is there an a.value property?
> >
> > I'm still concerned about using IS here.
> > Take for example that A is a particular object, and System.DBNull is
> another
> > object.
> > The IS operator is more appropriate to determine if "A" is the same
object
> > as DBNull, not the same value.
> >
> > Gerald
> >
> > "HS1" <(E-Mail Removed)> wrote in message
> > news:1098147081.668852@ftpsrv1...
> > > Thank you
> > >
> > > I tried to use =, the compiler get the error
> > >
> > > Operator '=' is not defined for types 'System.Object' and
> 'System.DBNull'.
> > > Use 'Is' operator to compare two reference types.
> > > Therefore, I have to change to "Is"
> > > I use VB.Net 2001
> > >
> > > Regards
> > > S.Hoa
> > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
message
> > > news:(E-Mail Removed)...
> > > > you got it, mostly.
> > > > i'm not certain if the IS keyword will give you the proper results
or
> > not.
> > > > this is not a value comparison, but an Object Reference comparison.
> > > > it would be safer to use:
> > > > If Not (a = DBNull.Value) Then
> > > >
> > > > or use the alternate test using
> > > > If Not IsDBNull(a) Then
> > > >
> > > > Gerald
> > > >
> > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > news:1098141920.570486@ftpsrv1...
> > > > > Thank you
> > > > > a is a value of a field in a table of a database. I have to check
it
> > is
> > > > null
> > > > > or not
> > > > > I have a solution
> > > > >
> > > > > If Not (a is DBNull.Value) Then
> > > > >
> > > > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
> > message
> > > > > news:(E-Mail Removed)...
> > > > > > What sort of "Null" are you looking for?
> > > > > > Database Null?
> > > > > > Object is Nothing?
> > > > > > a <> 0&?
> > > > > >
> > > > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > > > news:1098135675.785296@ftpsrv1...
> > > > > > > Hello
> > > > > > >
> > > > > > > Could you please help for a simple boolean expression
> > > > > > >
> > > > > > > If a is not equal to Null
> > > > > > >
> > > > > > > I tried
> > > > > > >
> > > > > > > If (a != null) Then
> > > > > > >
> > > > > > > This expression does not work
> > > > > > >
> > > > > > > I look at Help but can not find out
> > > > > > >
> > > > > > > Could you please help
> > > > > > >
> > > > > > > Thanks
> > > > > > > S.Hoa
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Thank you

"Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Ah, I see. Well, if it were me, I would explicitly cast the underlying
value
> to its appropriate sqltype then check for null. However, I do not know
what
> kind of underlying data you are dealing with.
> You could take the shortcut and use the Convert.IsDBNull which will handle
> an expression.
> Like so:
>
> If Convert.IsDBNull(DataGrid1.Item(DataGrid1.CurrentCell.RowNumber, 5))
Then
>
> It is possible that the way you are doing it will work fine. But it just
> seems dangerous to me.
>
> Gerald
>
> "HS1" <(E-Mail Removed)> wrote in message
> news:1098163724.554694@ftpsrv1...
> > Here is my code
> >
> > If (DataGrid1.Item(DataGrid1.CurrentCell.RowNumber, 5) Is DBNull.Value)
> Then
> >
> > In this code, dataGrid1 presents data for a table. I check the value
> > (textual type) of current row at column 5 to see that it is Null or not.
> >
> >
> > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in message
> > news:(E-Mail Removed)...
> > > What object type is "a"?
> > > You say a database field, but which object.
> > > Is there an a.value property?
> > >
> > > I'm still concerned about using IS here.
> > > Take for example that A is a particular object, and System.DBNull is
> > another
> > > object.
> > > The IS operator is more appropriate to determine if "A" is the same
> object
> > > as DBNull, not the same value.
> > >
> > > Gerald
> > >
> > > "HS1" <(E-Mail Removed)> wrote in message
> > > news:1098147081.668852@ftpsrv1...
> > > > Thank you
> > > >
> > > > I tried to use =, the compiler get the error
> > > >
> > > > Operator '=' is not defined for types 'System.Object' and
> > 'System.DBNull'.
> > > > Use 'Is' operator to compare two reference types.
> > > > Therefore, I have to change to "Is"
> > > > I use VB.Net 2001
> > > >
> > > > Regards
> > > > S.Hoa
> > > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
> message
> > > > news:(E-Mail Removed)...
> > > > > you got it, mostly.
> > > > > i'm not certain if the IS keyword will give you the proper results
> or
> > > not.
> > > > > this is not a value comparison, but an Object Reference
comparison.
> > > > > it would be safer to use:
> > > > > If Not (a = DBNull.Value) Then
> > > > >
> > > > > or use the alternate test using
> > > > > If Not IsDBNull(a) Then
> > > > >
> > > > > Gerald
> > > > >
> > > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > > news:1098141920.570486@ftpsrv1...
> > > > > > Thank you
> > > > > > a is a value of a field in a table of a database. I have to
check
> it
> > > is
> > > > > null
> > > > > > or not
> > > > > > I have a solution
> > > > > >
> > > > > > If Not (a is DBNull.Value) Then
> > > > > >
> > > > > > "Gerald Hernandez" <Cablewizard@(E-Mail Removed)> wrote in
> > > message
> > > > > > news:(E-Mail Removed)...
> > > > > > > What sort of "Null" are you looking for?
> > > > > > > Database Null?
> > > > > > > Object is Nothing?
> > > > > > > a <> 0&?
> > > > > > >
> > > > > > > "HS1" <(E-Mail Removed)> wrote in message
> > > > > > > news:1098135675.785296@ftpsrv1...
> > > > > > > > Hello
> > > > > > > >
> > > > > > > > Could you please help for a simple boolean expression
> > > > > > > >
> > > > > > > > If a is not equal to Null
> > > > > > > >
> > > > > > > > I tried
> > > > > > > >
> > > > > > > > If (a != null) Then
> > > > > > > >
> > > > > > > > This expression does not work
> > > > > > > >
> > > > > > > > I look at Help but can not find out
> > > > > > > >
> > > > > > > > Could you please help
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > > S.Hoa
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>