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From david myers <david.myers.scibearsp...@gmail.com>
Subject Re: NullPointerException in Derby 10.9.1.0
Date Mon, 03 Dec 2012 13:55:54 GMT
On 03/12/12 14:12, Knut Anders Hatlen wrote:
> Zorro <hz0885@gmail.com> writes:
>
>> Dear All,
>>
>> When doing in ij a bulk Insert into a table of my Derby database I do
>> get a NullPointerException.
> Hi Harm-Jan,
>
> It looks like you've come across a bug. I managed to reproduce the
> NullPointerException in my environment, so I filed a bug report and
> posted the steps I followed in order to reproduce it there:
> https://issues.apache.org/jira/browse/DERBY-6006
>
> Thanks for reporting the problem,
>
Hi Harm-Jan and Knut,

first off a bit of a long post, but I hope it may be informative...

I've just seen Knut's jira bug ([jira] (DERBY-6006)), and wonder (having 
looked at the stack trace that was posted) if the 'conglomerate' error 
at the top of the stack is related to a problem I experienced.

My problem can be recreated as follows....

 > Create a table in your db (any structure will do)
 > programatically take one of your fields and change its data type 
(from int to float for example).

    When you do this programatically the only way to do it is to...
     > create a new 'temp' field
     > copy the values from the original into the new
     > drop the original table
     > rename the 'temp' field so as you can use your table in your
    previously created routines etc...

 > the problem this creates is that the new 'temp' field, although for 
all intents is the 'same' as the original has a different value in the 
conglomerates tables.

Result:
     If you have use an external process that inserts data into the 
table from a select * the order of the fields has changed, and so the 
insert fails as the original fields have been 'shifted' to the left.

EG: Original table field order.
field1:field2:changeTypeOfThisfield:field3:field4:field5

new field after the modification.

field1:field2:field3:field4:field5:changedTypeOfThisField

Solution:

Programatically capture the names of the fields to ensure they stay in a 
'predefined' order.

The problem seen by Harm-Jan may have an similar solution, the problem 
being of course that it is now neccessary to programatically do the 
insert select (rather then being able to do it directly in ij), which 
seems a bit brutal.

So the reflection for Knut is: Is it possible to that internally the 
engine is creating a temp / shadow table and making a mess of these 
conglomerates during that process, and doing something like I have 
encountered (and how to test if the conglomerates are changing in this way)

If so my problem, which I have been considering calling a 'documentation 
bug' on, may be less benign and require a more involved solution.

Of course I may be off the mark, it was seeing the 'conglomerates error' 
that made me connect the 2 in my mind.

David.



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