Re: sorting xml nodes in freemarker

Thursday, February 4, 2010, 2:41:17 AM, Kunal wrote:

>
> Hi Daniel,
>
> Thanks for the reply. That really helped.
>
> However, my requirement is some thing like this. Consider the xml below
>
> <games>
>     <game name = "b">
>           <publisher>
>                <gameCompany name = "abc"></gameCompany>
>           </publisher>
>           <rating>9.0</rating>
>      </game>
>     <game name = "a">
>           <publisher>
>                <gameCompany name = "pqr"></gameCompany>
>           </publisher>
>      </game> 
>     <game name = "c">
>           <publisher>
>                <gameCompany name = "xyz"></gameCompany>
>           </publisher>
>           <rating>6.0</rating>
>     </game>
> </games> 
>
>
> I want to sort the game nodes based on the gameCompany name. How do I write
> the syntax?

Assuming doc stores the XML document:

  <#list doc.games.game?sort_by(['publisher', 'gameCompany', '@name']) as g>
    ${g.@@markup}
  </#list>

> Also, Suppose I want to sort on rating , when I write  
>
> [#list game_root.game?sort_by("rating") as game]
>
> I get the following error
> sort_by(...) failed: Values used for sorting must be numbers, strings, or
> date/time values.
> I suppose this error is because in the second game node rating node does not
> exist.

Yes, that's a problem (however, if you provide the default attribute
value with DTD then it may goes away... but I never tried that).
Another problem is that sorting numbers is not the same as sorting the
string representations of numbers, and XML stores text (OK, not
anymore with W3C Schemas, but FreeMarker doesn't know that). Like
"10.0" (the string) is less than "9.0".

> Is there any way I can still have the sorting done based on rating
> without changing the xml?

Unfortunately, ?sort_by is not powerful enough for this: it can't be
instructed to convert string values to numbers, and doesn't provide
default value for missing items. However, even the existence of
?sort/?sort_by is seen as something that's to powerful and thus
encourages bad practices... FreeMarker assumes that the data-model
contains the data already calculated, and that it only have to deal
with presentation issues. Sorting is mostly not that. Of course, if
you want to use FreeMarker to transform XML to XML, that's a different
story... but I never agreed with Jonathan in that FreeMarker should be
advertised as an XML transforming tool. It has some built-in features
to traverse XML in the data-model, but it still was made to and
remained an MVC-centric template engine.

Anyway... what can you do? Well, you could write a
TemplateMethodModelEx that does what you need (sort the tree nodes in
this and that way). (Or we should improve ?sort_by, but that certainly
won't happen soon if ever, as there is a lot of higher priority issues
piled up. Unless, you do it, test it, and sign the CLA.) Or, you could
preprocess the DOM tree before passing it to FreeMarker. Of course, if
you just wanted to transform XML to XML, these doesn't make much
sense... I can only point back to my statement that it's not in
general an XML transforming tool. /-:

> Thanks.
> Kunal

-- 
Best regards,
 Daniel Dekany


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