xpath_list() question for contrib/xml2 - Mailing list pgsql-general

From Ron Mayer
Subject xpath_list() question for contrib/xml2
Date
Msg-id 41F5989B.9040208@cheapcomplexdevices.com
Whole thread Raw
List pgsql-general
Short summary:

   I want something like xpath_list() that returns an array
   (instead of a delimited, concatenated string) when multiple
   nodes exist in an XML file.  It feels to me like that'd
   be a better (cleaner) API.

   Before I write one, does anyone already have such a
   patch?  If not, would people be interested if I added
   xpath_array() that behaves like xpath_list() but returns
   an array instead of one big string?

   Or... is xpsql on gborg or some other postgresql-xml
   project a better place for me to be looking?


Longer:

 From the (very cool) xml2 package's README, I see
   xpath_list(document,query,separator) RETURNS text
    This function returns multiple values separated by the specified
    separator, e.g. Value 1,Value 2,Value 3 if separator=','.

   xpath_list(document,query) RETURNS text
    This is a wrapper for the above function that
    uses ',' as the separator.

And indeed, that's exactly what it returns:

   fl=# create temporary table x (xml text);

   flee=# insert into x values
          ('<a><b id="1">1</b><b id="2">2</b></a>');
   flee=# select xpath_list(xml,'/a/b') from x;
    xpath_list
   ------------
    1,2
   (1 row)

However to make use of each value, I'd then need to re-parse
that text string to make use of each of the values.

I realize I can get the effect I want using an uncommon
string as a delimiter and the string_to_array() function...
  fl=# select
     string_to_array(xpath_list(xml,'/a/b','##delim##')
                                          ,'##delim##') from x;
     string_to_array
     -----------------
     {1,2}
     (1 row)
... but that feels pretty ugly considering to guess what
delimiter won't be in the string.



While I'm at it, a version of xpath_nodeset:
   fl=# select xpath_nodeset(xml,'/a/b') from x;
          xpath_nodeset
   --------------------------------
    <b id="1">1</b><b id="2">2</b>
   (1 row)
that returned an array of matching XML fragments
instead of all the fragments concatenated together
might also be useful.


Thoughts?  Suggestions?

   Ron


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