Comparison problem

[John]

Hi

I am trying to see if column forenames is empty/blank in a row in a
datatable. I am using the following statement to achieve that;

If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value.ToString) Then

I am getting the 'Operator is not valid for type 'DBNull' and string "".'
error on the above line. What am I doing wrong?

Thanks

Regards

[Scott M.]

You can not use the "=" operator for checking DBNull. Instead, use:

If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then

-Scott
"John" <jo**@nospam.infovis.co.uk> wrote in message
news:OY****************@TK2MSFTNGP11.phx.gbl...

Hi

I am trying to see if column forenames is empty/blank in a row in a
datatable. I am using the following statement to achieve that;

If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value.ToString) Then

I am getting the 'Operator is not valid for type 'DBNull' and string "".'
error on the above line. What am I doing wrong?

Thanks

Regards

[Miha Markic]

As Scott suggested:

If (mydatatable.Rows.Item(0).Item("Forenames") = System.DBNull.Value) Then

--
Miha Markic - RightHand .NET consulting & software development
miha at rthand com

"John" <jo**@nospam.infovis.co.uk> wrote in message
news:OY****************@TK2MSFTNGP11.phx.gbl...

Hi

I am trying to see if column forenames is empty/blank in a row in a
datatable. I am using the following statement to achieve that;

If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value.ToString) Then

I am getting the 'Operator is not valid for type 'DBNull' and string "".'
error on the above line. What am I doing wrong?

Thanks

Regards

[Armin Zingler]

"John" <jo**@nospam.infovis.co.uk> schrieb

I am trying to see if column forenames is empty/blank in a row in
a datatable. I am using the following statement to achieve that;

If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value.ToString) Then

I am getting the 'Operator is not valid for type 'DBNull' and string
"".' error on the above line. What am I doing wrong?

If mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull.Value Then
--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Paw Boel Nielsen]

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then (suggested by
Scott M.)
2) If (mydatatable.Rows.Item(0).Item("Forenames") = System.DBNull.Value)
Then (suggested by Miha Markic)
3) If mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull.Value Then
(suggested by Armin Zingler)

Out of curiosity what are the differences? (Is one way quicker than
another?)

Paw

"Armin Zingler" <az*******@freenet.de> wrote in message
news:O6**************@TK2MSFTNGP10.phx.gbl...

"John" <jo**@nospam.infovis.co.uk> schrieb

I am trying to see if column forenames is empty/blank in a row in
a datatable. I am using the following statement to achieve that;

If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value.ToString) Then

I am getting the 'Operator is not valid for type 'DBNull' and string
"".' error on the above line. What am I doing wrong?

If mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull.Value Then
--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Miha Markic]

Hi Paw,

"Paw Boel Nielsen" <no*@important.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then (suggested by Scott M.)
2) If (mydatatable.Rows.Item(0).Item("Forenames") = System.DBNull.Value)
Then (suggested by Miha Markic)
3) If mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull.Value Then (suggested by Armin Zingler)

Out of curiosity what are the differences? (Is one way quicker than
another?)

My is the fastest (2) beacuse it is a simple comparision while (3) is
probably the slowest because of type checking involved.
(1) is in the middle - it is slower than mine because it is a method and it
also checks the value agains null.

My humble opinion :)

--
Miha Markic - RightHand .NET consulting & development
miha at rthand com

[Cor]

Armin,

Is this datatable really working

If mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull.Value Then

The only thing I can understand it is:

If it is a dataset with the name "mydatatable" that has a table with the
name "Rows"

Where is my mistake

:-)

Cor

[Armin Zingler]

"Paw Boel Nielsen" <no*@important.com> schrieb

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then
(suggested by Scott M.)
2) If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value) Then (suggested by Miha Markic)
3) If mydatatable.Rows.Item(0).Item("Forenames") Is
System.DBNull.Value Then (suggested by Armin Zingler)

Out of curiosity what are the differences? (Is one way quicker
than another?)

4) If TypeOf mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull
Solution 1) does the same as 4), so 4) is faster because no function call is
involved.

2) is wrong because references have to be compared using the Is operator
--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Armin Zingler]

"Miha Markic" <miha at rthand com> schrieb

Hi Paw,

"Paw Boel Nielsen" <no*@important.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then
(suggested by

Scott M.)
2) If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value) Then (suggested by Miha Markic)
3) If mydatatable.Rows.Item(0).Item("Forenames") Is
System.DBNull.Value

Then

(suggested by Armin Zingler)

Out of curiosity what are the differences? (Is one way quicker
than another?)

My is the fastest (2) beacuse it is a simple comparision

References have to be compared using the Is operator.
2) leads to a compiler error. Sorry. ;-)
while (3)
is probably the slowest because of type checking involved.
No, it does not check the types, it only compares references.
(1) is in the middle - it is slower than mine because it is a method
and it also checks the value agains null.

My humble opinion :)

--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Armin Zingler]

"Cor" <no*@non.com> schrieb

Armin,

Is this datatable really working

If mydatatable.Rows.Item(0).Item("Forenames") Is
System.DBNull.Value Then

The only thing I can understand it is:

If it is a dataset with the name "mydatatable" that has a table with
the name "Rows"

Where is my mistake

:-)

??

I'd say:
If the field called "forenames" in the first row of the datable named
"mydatatable" references DBNull.Value then

:-)

--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

[Miha Markic]

Hi Armin,

"Armin Zingler" <az*******@freenet.de> wrote in message
news:uC**************@TK2MSFTNGP09.phx.gbl...

"Paw Boel Nielsen" <no*@important.com> schrieb

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then
(suggested by Scott M.)

4) If TypeOf mydatatable.Rows.Item(0).Item("Forenames") Is System.DBNull
Solution 1) does the same as 4), so 4) is faster because no function call is involved.
Yes, it is faster and no it does not the same thing. 1) checks also if value
is null.
Beware that if 1) and 4) do the same then they could be equal in terms of
speed if JIT optimizes 1) to inline calls.
2) is wrong because references have to be compared using the Is operator

Yeah, yeah, VB.NET.

--
Miha Markic - RightHand .NET consulting & software development
miha at rthand com

[Miha Markic]

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then
(suggested

by

Scott M.)
2) If (mydatatable.Rows.Item(0).Item("Forenames") =
System.DBNull.Value) Then (suggested by Miha Markic)
3) If mydatatable.Rows.Item(0).Item("Forenames") Is
System.DBNull.Value

Then

(suggested by Armin Zingler)

Out of curiosity what are the differences? (Is one way quicker
than another?)

My is the fastest (2) beacuse it is a simple comparision

References have to be compared using the Is operator.
2) leads to a compiler error. Sorry. ;-)

You sure on this?
Actually you are right - I've written it in C# and then not complectly
rewritten in VB.NET. Duh.

while (3)
is probably the slowest because of type checking involved.

No, it does not check the types, it only compares references.

Right. I was thinking in C# terms.

--
Miha Markic - RightHand .NET consulting & software development
miha at rthand com

[Armin Zingler]

"Miha Markic" <miha at rthand com> schrieb

Hi Armin,

"Armin Zingler" <az*******@freenet.de> wrote in message
news:uC**************@TK2MSFTNGP09.phx.gbl...

"Paw Boel Nielsen" <no*@important.com> schrieb

Ok so it seems there are 3 possible ways to check for nulls:

1) If IsDBNull(mydatatable.Rows.Item(0).Item("Forenames" ) Then
(suggested by Scott M.)

4) If TypeOf mydatatable.Rows.Item(0).Item("Forenames") Is
System.DBNull
Solution 1) does the same as 4), so 4) is faster because no
function call is

involved.

Yes, it is faster and no it does not the same thing. 1) checks also
if value is null.

Right. I meant "do the same" in the sense of "both compare the types"
(whereas the other one compares references)
Beware that if 1) and 4) do the same then they could be equal in
terms of speed if JIT optimizes 1) to inline calls.

Well, if a function does the same as the same code does outside the
function, they do the same. Of course, I agree, the function call itself
takes additional time.
2) is wrong because references have to be compared using the Is
operator

Yeah, yeah, VB.NET.

:-)
--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html