[xquery-talk] last possible child's attribute

[Christian Grün]

Hi Michalmas,
this one might help:  string(/descendant::@lc[last()])

Christian


On Sun, Mar 8, 2009 at 2:45 PM, Michalmas <michalmas at gmail.com> wrote:
> Hi,
>
> It still gives me the same error:
>
>> XQuery Serialization Error!
>> A document node may not have an attribute node or a namespace node as a
>> child
>
> @Ken:
> Yes, i meant last possible node that has a value for given attribute.
>
> On Sun, Mar 8, 2009 at 2:32 PM, G. Ken Holman
> <gkholman at cranesoftwrights.com> wrote:
>>
>> At 2009-03-08 13:43 +0100, Michalmas wrote:
>>>
>>> What i need to get in xquery is the last possible child's attribute.
>>
>> It looks to me like you need the last possible descendant's attribute, not
>> child.
>>
>>> Let's say i have following XML:
>>>
>>> <a>
>>>  <aa lc=1>
>>>     <aaa lc=00>
>>>     </aaa>
>>>  </aa>
>>>  <bb lc=0>
>>>  </bb>
>>>  <zz lc=1>
>>>     <ccc lc=123>
>>>     </ccc>
>>>  </zz>
>>> </a>
>>>
>>> and i want to get the last child of 'a' node. So, in this case, it would
>>> be node 'ccc'. Then, i want to get lc attribute - in this example, 123.
>>
>> Two ways you could express it, based on how easy you think each will be
>> maintained by someone reading your code:
>>
>> To be explicit, you want the attribute of the last descendant of the
>> element:
>>
>>  a/descendant::*[last()]/@lc
>>
>> To be concise, you want the last attribute descending from the element:
>>
>>  (a//@lc)[last()]
>>
>> The code below shows both of those working ... and I doubt there would be
>> any difference in execution time ... choose whichever one "reads" better
>> from a maintenance perspective.
>>
>> I believe maintenance of transforms is as important as performance ... let
>> the processor worry about the optimization of the performance.
>>
>> BTW, I'm assuming you know the attribute's name.  There is no such concept
>> as "last specified attribute" for a given element, because attributes along
>> the attribute axis are in an arbitrary order, they are not in specified
>> order.  I find many students assume that just because they specified
>> attributes in a particular order they are going to find them in that order
>> when they walk the attribute axis.  XML says that attributes are unordered.
>>  In the data model, they have an order, you just don't know what that order
>> is.  So you can reliably walk over an attribute axis multiple times in one
>> transformation and get the attributes in the same order each time during
>> that transformation, but they won't necessarily be in that order the next
>> time or with another processor.
>>
>> I hope this helps.
>>
>> . . . . . . . . . . Ken
>>
>> t:\ftemp>type michalmas.xml
>> <a>
>>  <aa lc="1">
>>     <aaa lc="00">
>>     </aaa>
>>  </aa>
>>  <bb lc="0">
>>  </bb>
>>  <zz lc="1">
>>     <ccc lc="123">
>>     </ccc>
>>  </zz>
>> </a>
>>
>> t:\ftemp>type michalmas.xq
>> string( a/descendant::*[last()]/@lc ),
>> string( (a//@lc)[last()] )
>> t:\ftemp>xquery michalmas.xml michalmas.xq
>> <?xml version="1.0" encoding="UTF-8"?>123 123
>> t:\ftemp>
>>
>> --
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>> G. Ken Holman                 mailto:gkholman at CraneSoftwrights.com
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>
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-- 
___________________________

Christian Gruen
Universitaet Konstanz
Department of Computer & Information Science
D-78457 Konstanz, Germany
Tel: +49 (0)7531/88-4449, Fax: +49 (0)7531/88-3577
http://www.inf.uni-konstanz.de/~gruen