Re: Possible Type Conversion Defect
- From: David Klebanoff <DavidKlebanoff@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 8 Dec 2005 18:04:01 -0800
Angel, we have a very serious issue with this choice of type conversion
behaviour. At the moment, our application will simply not run with the Beta 2
driver.
Specifically we are breaking due to the lack of conversion from BIGINT to
int. However, I am not ruling out other type conversion issues that may
surface later (right now I can't run the app at all until I deal with this
particular one).
As you pointed out, this behaviour is inconsistent with the previous
Microsoft SQL Server 2000 JDBC driver. But it is also inconsistent with the
other major drivers, namely IBM DB2, IBM DB2 z/OS, Oracle 9i and Oracle 10g
(which incidentally, we must also support from the same codebase). All of
these drivers will narrow the type and throw if the value is out of range or
unconvertable.
I'll agree that the JDBC API specifications could be a bit more precise.
However, the documentation for the ResultSet class says: "For the getter
methods, a JDBC driver attempts to convert the underlying data to the Java
type specified in the getter method and returns a suitable Java value. The
JDBC specification has a table showing the allowable mappings from SQL types
to Java types that can be used by the ResultSet getter methods. " BIGINT->int
is shown as allowed in the JDBC specification.
But this isn't the real point. The real point is that it is critical to
preserve existing behaviour. If you want to change existing behaviour,
particularly in a way that can break deployed software, then you need to make
it parametrically controllable.
Please reconsider this strategy.
David Klebanoff
"Angel Saenz-Badillos[MS]" wrote:
> Thank you for your feedback, as you mention this is going to impact existing
> code and we are nervous to see how specific areas are affecting customers.
> We believe that this is the right story going forward but we may have to
> bend it a little for specific customer scenarios. We have already received
> some pushback on getObject for uniqueIdentifiers (currently returns a byte
> array which is how the server stores it but is not particularily usefull)
> and supporting getLong on a Numeric(Decimal) type. If you have any other
> suggestions be sure to post them here or file them as bug in the msdn
> product feedback site :
> http://lab.msdn.microsoft.com/productfeedback/default.aspx
>
> There is still time to integrate customer feedback into this data coercion
> story, but it is running out fast.
>
> --
> Angel Saenz-Badillos [MS] DataWorks
> This posting is provided "AS IS", with no warranties, and confers no
> rights.Please do not send email directly to this alias.
> This alias is for newsgroup purposes only.
> I am now blogging: http://weblogs.asp.net/angelsb/
>
>
>
>
> "Eric Molitor" <EricMolitor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:3D094877-F2AC-4E91-9FDB-324FBB29BCD5@xxxxxxxxxxxxxxxx
> > Right, I dug into this and was able to solve the problems both with
> > conversions and by fixing some bad practices in our SQL...
> >
> > In several places after executing an insert we would simply...
> >
> > select @@IDENTITY as identityValue
> >
> > and then retrieve the value from the result set in java. Obviously we
> > should
> > have been using SCOPE_IDENTITY() for one but also we should have been
> > using
> > an out put parameter...
> >
> > So the proc becomes
> >
> > CREATE PROCEDURE spTestProc
> > (
> > @username varchar(8),
> > @firstname varchar(255),
> > @lastname varchar(255),
> > @UserID int OUTPUT
> > ) as
> >
> > INSERT INTO User (username, firstname, lastname)
> > VALUES (@username, @firstname, @lastname)
> >
> > SELECT @UserID = SCOPE_IDENTITY()
> >
> > and in the code we just fetch the value as an output parameter...
> >
> > So once all of this shakes out I do think it will be a positive change,
> > however I'm sure lots of people will have some SQL and Java to cleanup.
> >
> > Cheers,
> > Eric
> >
> >
> >
> > "Angel Saenz-Badillos[MS]" wrote:
> >
> >> We wanted to be very explicit with our data coercion story and as far as
> >> we
> >> have been able we are not going to allow getting a type from the server
> >> that
> >> would require a downcast to the client and possible loss of data. This
> >> strategy has the advantage of high predictability with limited chance of
> >> data loss, but it is very restrictive.
> >>
> >> Quite frankly I was expecting to see a lot more people commenting on
> >> these.
> >> In your case 108 is of type NUMERIC, a 38bit precission decimal and you
> >> are
> >> trying to shove it into an INTEGER. Type 38 is an INTEGER which does not
> >> fit
> >> on a SMALLINT.
> >>
> >> We only have two choices here that don't involve data loss (something we
> >> are
> >> definitelly not going to allow),
> >> 1) We can NEVER allow a conversion from a type if _the type you are
> >> trying
> >> to convert_ does not fit into the type that you are trying to coerce it
> >> into. This is the behavior that we have opted for in the 2005 JDBC
> >> driver.
> >>
> >> 2) We can allow a conversion from a type that does not fit into the
> >> coreced
> >> type _only_ when the current value that you are asking for can be coerced
> >> into the type that you are asking for. This is the behavior of the 2000
> >> JDBC
> >> driver.
> >>
> >> Let's say that you have a NUMERIC column that has a value of 5, when you
> >> call getInt on this we will throw an exception if following (1) but the
> >> coercion will work on a driver that supports (2) since 5 does fit into an
> >> INTEGER type. When you have a driver that provides the (1) functionality
> >> you
> >> will realize the first time you run your code that a NUMERIC column will
> >> not
> >> always fit into an int and change your code accordingly. When working
> >> with a
> >> driver of the (2) type you will test and deploy your application with
> >> getInt. When the value of the NUMERIC column goes over what an INTEGER
> >> can
> >> handle you will get a runtime exception and you will have to go service
> >> your
> >> deployed application.
> >>
> >> We realize that it can be inconvenient to have this kind of issues
> >> surfaced
> >> early, but we feel it is better to let you know up front about possible
> >> data
> >> coercion issues, if you really wanted to get an integer from the server
> >> you
> >> would have defined your table accordingly, or you could have requested an
> >> integer in your query with the CONVERT function.
> >>
> >> I think that this is going to be a common question, I am going to convert
> >> this post into a blog and post it into the
> >> http://blogs.msdn.com/dataaccess/
> >> with a complete data coercion table to help make this design clearer, of
> >> course comments/suggestions are welcome.
> >> --
> >> Angel Saenz-Badillos [MS] DataWorks
> >> This posting is provided "AS IS", with no warranties, and confers no
> >> rights.Please do not send email directly to this alias.
> >> This alias is for newsgroup purposes only.
> >> I am now blogging: http://weblogs.asp.net/angelsb/
> >>
> >>
> >>
> >>
> >> "Eric Molitor" <EricMolitor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> >> news:237EAB6D-63BA-4DB2-AB0C-7EB8D98B3E2D@xxxxxxxxxxxxxxxx
> >> > Seem to be getting these consistantly in certain portions of our
> >> > application.
> >> > Works fine with the older JDBC driver (2000) but under the 2005 driver
> >> > we
> >> > see....
> >> >
> >> > com.microsoft.sqlserver.jdbc.SQLServerException: Unsupported conversion
> >> > from
> >> > 108 to INTEGER
> >> > at
> >> > com.microsoft.sqlserver.jdbc.SQLServerStatement.getRowsetField(Unknown
> >> > Source)
> >> > at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getInt(Unknown
> >> > Source)
> >> > at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getInt(Unknown
> >> > Source)
> >> >
> >> > and
> >> >
> >> > com.microsoft.sqlserver.jdbc.SQLServerException: Unsupported conversion
> >> > from
> >> > 38 to SMALLINT
> >> > at
> >> > com.microsoft.sqlserver.jdbc.SQLServerStatement.getRowsetField(Unknown
> >> > Source)
> >> > at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getShort(Unknown
> >> > Source)
> >> > at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getShort(Unknown
> >> > Source)
> >> >
> >> > I'm looking at the SQL and the code but I'd think 38 is a valid
> >> > SMALLINT
> >> > and
> >> > that 108 is a valid INTEGER.
> >> >
> >> >
> >>
> >>
> >>
>
>
>
.
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