Design issue: Handling null datetimes from legacy databases. - DOTNET

http://www.google.com/search?hl=en&q...+nullable+C%23

http://www.c-sharpcorner.com/UploadF...abletypes.aspx


You can google search "nullable datetime" and find some stuff.

The second URL above is one I picked.


Luckily, you are at using (at least) 2.0.



.........




"B. Chernick" <BChernick@discussions.microsoft.com> wrote in message
news:18012C94-C53D-49BB-BE29-BDA5A4278EEA@microsoft.com...
> I'm writing a demo website in VB/Dot Net 2.0. The database is SQL 2000
> and
> the design is at least partially legacy. (And this is the first real web
> work I've done in 2.0. All previous work was in 1.1) It is my intent to
> stay as close to defaults as possible: i.e. using the most generic
> techniques
> possible with as little coding as possible.
>
> My existing database table has some datetime field values that are null.
> I
> have a page with a detailsview bound to a record in that table. The
> datetime fields on my webpage are templates. The read-only screen has no
> problem displaying the record, but when I hit the Edit link, the page
> crashes
> with the message: 'Conversion from type 'DBNull' to type 'Date' is not
> valid.' So far I have not been able to intercept this in VB code.
>
> Apparently it is useless to set the field's xsd default property to
> something like '1/1/1900' or '1/1/1753'. I still get the crash. Also I
> cannot set the NullValue property to anything other than (Throw Exception)
> when the field is a datetime.
>
> I'm getting the impression from my reading that the best approach is to
> not
> permit null datetimes in the first place and that I should simply revise
> the
> database table.
>
> Suggestions?

Thanks but so far I don't get it. I simply dragged a table onto the xsd and
bound it to a detailsview with almost no coding. Is this type of code (the
c-sharpcorner example) supposed to be put in the xsd's code behind? The xsd
itself can't handle nullable declarations.

"sloan" wrote:

> http://www.google.com/search?hl=en&q...+nullable+C%23
>
> http://www.c-sharpcorner.com/UploadF...abletypes.aspx
>
>
> You can google search "nullable datetime" and find some stuff.
>
> The second URL above is one I picked.
>
>
> Luckily, you are at using (at least) 2.0.
>
>
>
> .........
>
>
>
>
> "B. Chernick" <BChernick@discussions.microsoft.com> wrote in message
> news:18012C94-C53D-49BB-BE29-BDA5A4278EEA@microsoft.com...
> > I'm writing a demo website in VB/Dot Net 2.0. The database is SQL 2000
> > and
> > the design is at least partially legacy. (And this is the first real web
> > work I've done in 2.0. All previous work was in 1.1) It is my intent to
> > stay as close to defaults as possible: i.e. using the most generic
> > techniques
> > possible with as little coding as possible.
> >
> > My existing database table has some datetime field values that are null.
> > I
> > have a page with a detailsview bound to a record in that table. The
> > datetime fields on my webpage are templates. The read-only screen has no
> > problem displaying the record, but when I hit the Edit link, the page
> > crashes
> > with the message: 'Conversion from type 'DBNull' to type 'Date' is not
> > valid.' So far I have not been able to intercept this in VB code.
> >
> > Apparently it is useless to set the field's xsd default property to
> > something like '1/1/1900' or '1/1/1753'. I still get the crash. Also I
> > cannot set the NullValue property to anything other than (Throw Exception)
> > when the field is a datetime.
> >
> > I'm getting the impression from my reading that the best approach is to
> > not
> > permit null datetimes in the first place and that I should simply revise
> > the
> > database table.
> >
> > Suggestions?
>
>
>

This is one reason to go to the custom business object model, instead of
relying on "quickie" (rapid development) DataSets.

See:
http://sholliday.spaces.live.com/Blo...842A!140.entry

for an example of custom business objects/ custom collections.






"B. Chernick" <BChernick@discussions.microsoft.com> wrote in message
news:3E37B883-74A4-4857-AFE3-5920B1C816DF@microsoft.com...
> Thanks but so far I don't get it. I simply dragged a table onto the xsd
> and
> bound it to a detailsview with almost no coding. Is this type of code
> (the
> c-sharpcorner example) supposed to be put in the xsd's code behind? The
> xsd
> itself can't handle nullable declarations.
>
> "sloan" wrote:
>
>> http://www.google.com/search?hl=en&q...+nullable+C%23
>>
>> http://www.c-sharpcorner.com/UploadF...abletypes.aspx
>>
>>
>> You can google search "nullable datetime" and find some stuff.
>>
>> The second URL above is one I picked.
>>
>>
>> Luckily, you are at using (at least) 2.0.
>>
>>
>>
>> .........
>>
>>
>>
>>
>> "B. Chernick" <BChernick@discussions.microsoft.com> wrote in message
>> news:18012C94-C53D-49BB-BE29-BDA5A4278EEA@microsoft.com...
>> > I'm writing a demo website in VB/Dot Net 2.0. The database is SQL 2000
>> > and
>> > the design is at least partially legacy. (And this is the first real
>> > web
>> > work I've done in 2.0. All previous work was in 1.1) It is my intent
>> > to
>> > stay as close to defaults as possible: i.e. using the most generic
>> > techniques
>> > possible with as little coding as possible.
>> >
>> > My existing database table has some datetime field values that are
>> > null.
>> > I
>> > have a page with a detailsview bound to a record in that table. The
>> > datetime fields on my webpage are templates. The read-only screen has
>> > no
>> > problem displaying the record, but when I hit the Edit link, the page
>> > crashes
>> > with the message: 'Conversion from type 'DBNull' to type 'Date' is not
>> > valid.' So far I have not been able to intercept this in VB code.
>> >
>> > Apparently it is useless to set the field's xsd default property to
>> > something like '1/1/1900' or '1/1/1753'. I still get the crash.
>> > Also I
>> > cannot set the NullValue property to anything other than (Throw
>> > Exception)
>> > when the field is a datetime.
>> >
>> > I'm getting the impression from my reading that the best approach is to
>> > not
>> > permit null datetimes in the first place and that I should simply
>> > revise
>> > the
>> > database table.
>> >
>> > Suggestions?
>>
>>
>>