Thread: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
David Fetter
Date:
== Submission review ==

* Is the patch in context diff format?

    Yes.

* Does it apply cleanly to the current CVS HEAD?

    Yes.

    patch -p1 < ../xpath_exists-3.patch
    patching file doc/src/sgml/func.sgml
    Hunk #1 succeeded at 8642 (offset 16 lines).
    patching file src/backend/utils/adt/xml.c
    patching file src/include/catalog/pg_proc.h
    Hunk #1 succeeded at 4391 (offset 6 lines).
    patching file src/include/utils/xml.h
    patching file src/test/regress/expected/xml.out
    patching file src/test/regress/sql/xml.sql

* Does it include reasonable tests, necessary doc patches, etc?

    Tests:

        As this is new functionality, it doesn't really need to test
        much for interactions with other parts of the system.

        I'm not really an XML expert, so I'd like to punt as to
        whether it tests enough functionality.

        Minor quibble with the regression tests: should we be using
        dollar quotes in things like this?  Doubled-up quote marks:

        SELECT xpath_exists('//town[text() =
''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);

        Dollar quote:

        SELECT xpath_exists($$//town[text() =
'Cwmbran']$$,'<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);


    Doc patches: Good up to cross-Atlantic differences in spelling
    (speciali[sz]ed), e.g.

== Usability review ==

Read what the patch is supposed to do, and consider:

* Does the patch actually implement that?

    Yes.

* Do we want that?

    Yes.

* Do we already have it?

    Not really.  There are kludges to accomplish these things, but
    they're available mostly in the sense that a general-purpose
    language allows you to write code to do anything a Turing machine
    can do.

* Does it follow SQL spec, or the community-agreed behavior?

    Yes.

* Does it include pg_dump support (if applicable)?

    Not applicable.

* Are there dangers?

    Not that I can see.

* Have all the bases been covered?

    To the extent of my XML knowledge, yes.

== Feature test ==

Apply the patch, compile it and test:

* Does the feature work as advertised?

    Yes.

* Are there corner cases the author has failed to consider?

    Not that I've found.  See above re: XML and my vast ignorance of
    same.

* Are there any assertion failures or crashes?

    No.

== Performance review ==

* Does the patch slow down simple tests?

    No.

* If it claims to improve performance, does it?

    No such claim made.  The kludges needed to reproduce the
    functionality would certainly consume an enormous number of
    developer hours, though.

* Does it slow down other things?

    Not that I've found.  There might be some minuscule slowing down
    of the code to the existence of more code paths, but we're a long,
    long way from having that be something other than noise.

== Coding review ==

Read the changes to the code in detail and consider:

* Does it follow the project [http://developer.postgresql.org/pgdocs/postgres/source.html coding guidelines]?

    Yes.

* Are there portability issues?

    Not that I can see.

* Will it work on Windows/BSD etc?

    Should do.

* Are the comments sufficient and accurate?

    Yes.

* Does it do what it says, correctly?

    Yes, subject to, etc.

* Does it produce compiler warnings?

    No.

* Can you make it crash?

    No.

== Architecture review ==

Consider the changes to the code in the context of the project as a whole:

* Is everything done in a way that fits together coherently with other features/modules?

    Yes.

* Are there interdependencies that can cause problems?

    Not that I've found.

Cheers,
David.
On Tue, Jun 29, 2010 at 11:37:28AM +0100, Mike Fowler wrote:
> Mike Fowler wrote:
> >Bruce Momjian wrote:
> >>I have added this to the next commit-fest:
> >>
> >>    https://commitfest.postgresql.org/action/commitfest_view?id=6
> >Thanks Bruce. Attached is a revised patch which changes the code
> >slightly such that it uses an older version of the libxml library.
> >I've added comments to the code so that we remember why we didn't
> >use the latest function.
>
> After seeing some other posts in the last couple of days, I realised
> I hadn't documented the function in the SGML. I have now done so,
> and added a couple of tests with XML literals. Please find the patch
> attached. Now time to go correct the xmlexists patch too...
>
> --
> Mike Fowler
> Registered Linux user: 379787
>

> *** a/doc/src/sgml/func.sgml
> --- b/doc/src/sgml/func.sgml
> ***************
> *** 8626,8631 **** SELECT xpath('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
> --- 8626,8664 ----
>   (1 row)
>   ]]></screen>
>      </para>
> +
> +    <sect3>
> +     <title>xpath_exists</title>
> +
> +     <indexterm>
> +      <primary>xpath_exists</primary>
> +     </indexterm>
> +
> +     <synopsis>
> +      <function>xpath_exists</function>(<replaceable>xpath</replaceable>, <replaceable>xml</replaceable><optional>,
<replaceable>nsarray</replaceable></optional>)
> +     </synopsis>
> +
> +     <para>
> +      The function <function>xpath_exists</function> is a specialised form
> +      of the <function>xpath</function> function. Though the functions are
> +      syntactically the same the xpath expressions are evaluated in differing
> +      contexts. Instead of returning the XML values that satisfy the xpath, this
> +      function returns a boolean indicating whether the query was satisfied or not.
> +     </para>
> +
> +     <para>
> +      Example:
> +      <screen><![CDATA[
> + SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
> +                     ARRAY[ARRAY['my', 'http://example.com']]);
> +
> +  xpath_exists
> + ------------
> +  t
> + (1 row)
> + ]]></screen>
> +     </para>
> +    </sect3>
>     </sect2>
>
>     <sect2 id="functions-xml-mapping">
> *** a/src/backend/utils/adt/xml.c
> --- b/src/backend/utils/adt/xml.c
> ***************
> *** 3495,3497 **** xpath(PG_FUNCTION_ARGS)
> --- 3495,3681 ----
>       return 0;
>   #endif
>   }
> +
> + /*
> +  * Determines if the node specified by the supplied XPath exists
> +  * in a given XML document, returning a boolean.
> +  *
> +  * It is up to the user to ensure that the XML passed is in fact
> +  * an XML document - XPath doesn't work easily on fragments without
> +  * a context node being known.
> +  */
> + Datum
> + xpath_exists(PG_FUNCTION_ARGS)
> + {
> + #ifdef USE_LIBXML
> +     text       *xpath_expr_text = PG_GETARG_TEXT_P(0);
> +     xmltype    *data = PG_GETARG_XML_P(1);
> +     ArrayType  *namespaces = PG_GETARG_ARRAYTYPE_P(2);
> +     ArrayBuildState *astate = NULL;
> +     xmlParserCtxtPtr ctxt = NULL;
> +     xmlDocPtr    doc = NULL;
> +     xmlXPathContextPtr xpathctx = NULL;
> +     xmlXPathCompExprPtr xpathcomp = NULL;
> +     xmlXPathObjectPtr xpathobj = NULL;
> +     char       *datastr;
> +     int32        len;
> +     int32        xpath_len;
> +     xmlChar    *string;
> +     xmlChar    *xpath_expr;
> +     int            i;
> +     int            res_nitems;
> +     int            ndim;
> +     Datum       *ns_names_uris;
> +     bool       *ns_names_uris_nulls;
> +     int            ns_count;
> +     int            result;
> +
> +     /*
> +      * Namespace mappings are passed as text[].  If an empty array is passed
> +      * (ndim = 0, "0-dimensional"), then there are no namespace mappings.
> +      * Else, a 2-dimensional array with length of the second axis being equal
> +      * to 2 should be passed, i.e., every subarray contains 2 elements, the
> +      * first element defining the name, the second one the URI.  Example:
> +      * ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
> +      * 'http://example2.com']].
> +      */
> +     ndim = ARR_NDIM(namespaces);
> +     if (ndim != 0)
> +     {
> +         int           *dims;
> +
> +         dims = ARR_DIMS(namespaces);
> +
> +         if (ndim != 2 || dims[1] != 2)
> +             ereport(ERROR,
> +                     (errcode(ERRCODE_DATA_EXCEPTION),
> +                      errmsg("invalid array for XML namespace mapping"),
> +                      errdetail("The array must be two-dimensional with length of the second axis equal to 2.")));
> +
> +         Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);
> +
> +         deconstruct_array(namespaces, TEXTOID, -1, false, 'i',
> +                           &ns_names_uris, &ns_names_uris_nulls,
> +                           &ns_count);
> +
> +         Assert((ns_count % 2) == 0);    /* checked above */
> +         ns_count /= 2;            /* count pairs only */
> +     }
> +     else
> +     {
> +         ns_names_uris = NULL;
> +         ns_names_uris_nulls = NULL;
> +         ns_count = 0;
> +     }
> +
> +     datastr = VARDATA(data);
> +     len = VARSIZE(data) - VARHDRSZ;
> +     xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
> +     if (xpath_len == 0)
> +         ereport(ERROR,
> +                 (errcode(ERRCODE_DATA_EXCEPTION),
> +                  errmsg("empty XPath expression")));
> +
> +     string = (xmlChar *) palloc((len + 1) * sizeof(xmlChar));
> +     memcpy(string, datastr, len);
> +     string[len] = '\0';
> +
> +     xpath_expr = (xmlChar *) palloc((xpath_len + 1) * sizeof(xmlChar));
> +     memcpy(xpath_expr, VARDATA(xpath_expr_text), xpath_len);
> +     xpath_expr[xpath_len] = '\0';
> +
> +     pg_xml_init();
> +     xmlInitParser();
> +
> +     PG_TRY();
> +     {
> +         /*
> +          * redundant XML parsing (two parsings for the same value during one
> +          * command execution are possible)
> +          */
> +         ctxt = xmlNewParserCtxt();
> +         if (ctxt == NULL)
> +             xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
> +                         "could not allocate parser context");
> +         doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
> +         if (doc == NULL)
> +             xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
> +                         "could not parse XML document");
> +         xpathctx = xmlXPathNewContext(doc);
> +         if (xpathctx == NULL)
> +             xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
> +                         "could not allocate XPath context");
> +         xpathctx->node = xmlDocGetRootElement(doc);
> +         if (xpathctx->node == NULL)
> +             xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
> +                         "could not find root XML element");
> +
> +         /* register namespaces, if any */
> +         if (ns_count > 0)
> +         {
> +             for (i = 0; i < ns_count; i++)
> +             {
> +                 char       *ns_name;
> +                 char       *ns_uri;
> +
> +                 if (ns_names_uris_nulls[i * 2] ||
> +                     ns_names_uris_nulls[i * 2 + 1])
> +                     ereport(ERROR,
> +                             (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
> +                       errmsg("neither namespace name nor URI may be null")));
> +                 ns_name = TextDatumGetCString(ns_names_uris[i * 2]);
> +                 ns_uri = TextDatumGetCString(ns_names_uris[i * 2 + 1]);
> +                 if (xmlXPathRegisterNs(xpathctx,
> +                                        (xmlChar *) ns_name,
> +                                        (xmlChar *) ns_uri) != 0)
> +                     ereport(ERROR,        /* is this an internal error??? */
> +                             (errmsg("could not register XML namespace with name \"%s\" and URI \"%s\"",
> +                                     ns_name, ns_uri)));
> +             }
> +         }
> +
> +         xpathcomp = xmlXPathCompile(xpath_expr);
> +         if (xpathcomp == NULL)    /* TODO: show proper XPath error details */
> +             xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
> +                         "invalid XPath expression");
> +
> +         /* Version 2.6.27 introduces a function named xmlXPathCompiledEvalToBoolean
> +          * however we can derive the existence by whether any nodes are returned
> +          * thereby preventing a library version upgrade */
> +         xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
> +         if (xpathobj == NULL)    /* TODO: reason? */
> +             xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
> +                         "could not create XPath object");
> +
> +         if (xpathobj->nodesetval == NULL)
> +             result = 0;
> +         else
> +             result = xpathobj->nodesetval->nodeNr;
> +     }
> +     PG_CATCH();
> +     {
> +         if (xpathobj)
> +             xmlXPathFreeObject(xpathobj);
> +         if (xpathcomp)
> +             xmlXPathFreeCompExpr(xpathcomp);
> +         if (xpathctx)
> +             xmlXPathFreeContext(xpathctx);
> +         if (doc)
> +             xmlFreeDoc(doc);
> +         if (ctxt)
> +             xmlFreeParserCtxt(ctxt);
> +         PG_RE_THROW();
> +     }
> +     PG_END_TRY();
> +
> +     xmlXPathFreeCompExpr(xpathcomp);
> +     xmlXPathFreeContext(xpathctx);
> +     xmlFreeDoc(doc);
> +     xmlFreeParserCtxt(ctxt);
> +
> +     PG_RETURN_BOOL(result);
> + #else
> +     NO_XML_SUPPORT();
> +     return 0;
> + #endif
> + }
> *** a/src/include/catalog/pg_proc.h
> --- b/src/include/catalog/pg_proc.h
> ***************
> *** 4385,4390 **** DESCR("evaluate XPath expression, with namespaces support");
> --- 4385,4395 ----
>   DATA(insert OID = 2932 (  xpath         PGNSP PGUID 14 1 0 0 f f f t f i 2 0 143 "25 142" _null_ _null_ _null_
_null_"select pg_catalog.xpath($1, $2, ''{}''::pg_catalog.text[])" _null_ _null_ _null_ )); 
>   DESCR("evaluate XPath expression");
>
> + DATA(insert OID = 3037 (  xpath_exists     PGNSP PGUID 12 1 0 0 f f f t f i 3 0 16 "25 142 1009" _null_ _null_
_null__null_ xpath_exists _null_ _null_ _null_ )); 
> + DESCR("evaluate XPath expression in a boolean context, with namespaces support");
> + DATA(insert OID = 3038 (  xpath_exists     PGNSP PGUID 14 1 0 0 f f f t f i 2 0 16 "25 142" _null_ _null_ _null_
_null_"select pg_catalog.xpath_exists($1, $2, ''{}''::pg_catalog.text[])" _null_ _null_ _null_ )); 
> + DESCR("evaluate XPath expression in a boolean context");
> +
>   /* uuid */
>   DATA(insert OID = 2952 (  uuid_in           PGNSP PGUID 12 1 0 0 f f f t f i 1 0 2950 "2275" _null_ _null_ _null_
_null_uuid_in _null_ _null_ _null_ )); 
>   DESCR("I/O");
> *** a/src/include/utils/xml.h
> --- b/src/include/utils/xml.h
> ***************
> *** 37,42 **** extern Datum texttoxml(PG_FUNCTION_ARGS);
> --- 37,43 ----
>   extern Datum xmltotext(PG_FUNCTION_ARGS);
>   extern Datum xmlvalidate(PG_FUNCTION_ARGS);
>   extern Datum xpath(PG_FUNCTION_ARGS);
> + extern Datum xpath_exists(PG_FUNCTION_ARGS);
>
>   extern Datum table_to_xml(PG_FUNCTION_ARGS);
>   extern Datum query_to_xml(PG_FUNCTION_ARGS);
> *** a/src/test/regress/expected/xml.out
> --- b/src/test/regress/expected/xml.out
> ***************
> *** 502,504 **** SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
> --- 502,557 ----
>    {<b>two</b>,<b>etc</b>}
>   (1 row)
>
> + -- Test xpath_exists evaluation
> + SELECT xpath_exists('//town[text() =
''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
> +  xpath_exists
> + --------------
> +  f
> + (1 row)
> +
> + SELECT xpath_exists('//town[text() =
''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
> +  xpath_exists
> + --------------
> +  t
> + (1 row)
> +
> + INSERT INTO xmltest VALUES (4,
'<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
> + INSERT INTO xmltest VALUES (5,
'<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
> + INSERT INTO xmltest VALUES (6, '<myns:menu
xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
> + INSERT INTO xmltest VALUES (7, '<myns:menu
xmlns:myns="http://myns.com"><myns:beers><myns:name>Molson</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beer',data);
> +  count
> + -------
> +      0
> + (1 row)
> +
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers',data);
> +  count
> + -------
> +      2
> + (1 row)
> +
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers/name[text() = ''Molson'']',data);
> +  count
> + -------
> +      1
> + (1 row)
> +
> + SELECT COUNT(id) FROM xmltest WHERE
xpath_exists('/myns:menu/myns:beer',data,ARRAY[ARRAY['myns','http://myns.com']]);
> +  count
> + -------
> +      0
> + (1 row)
> +
> + SELECT COUNT(id) FROM xmltest WHERE
xpath_exists('/myns:menu/myns:beers',data,ARRAY[ARRAY['myns','http://myns.com']]);
> +  count
> + -------
> +      2
> + (1 row)
> +
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers/myns:name[text() =
''Molson'']',data,ARRAY[ARRAY['myns','http://myns.com']]);
> +  count
> + -------
> +      1
> + (1 row)
> +
> *** a/src/test/regress/sql/xml.sql
> --- b/src/test/regress/sql/xml.sql
> ***************
> *** 163,165 **** SELECT xpath('', '<!-- error -->');
> --- 163,181 ----
>   SELECT xpath('//text()', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number
one</local:piece><local:pieceid="2" /></local:data>'); 
>   SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><local:piece id="1">number
one</local:piece><local:pieceid="2" /></local:data>', ARRAY[ARRAY['loc', 'http://127.0.0.1']]); 
>   SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
> +
> + -- Test xpath_exists evaluation
> + SELECT xpath_exists('//town[text() =
''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
> + SELECT xpath_exists('//town[text() =
''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
> +
> + INSERT INTO xmltest VALUES (4,
'<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
> + INSERT INTO xmltest VALUES (5,
'<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
> + INSERT INTO xmltest VALUES (6, '<myns:menu
xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
> + INSERT INTO xmltest VALUES (7, '<myns:menu
xmlns:myns="http://myns.com"><myns:beers><myns:name>Molson</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);
> +
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beer',data);
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers',data);
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/menu/beers/name[text() = ''Molson'']',data);
> + SELECT COUNT(id) FROM xmltest WHERE
xpath_exists('/myns:menu/myns:beer',data,ARRAY[ARRAY['myns','http://myns.com']]);
> + SELECT COUNT(id) FROM xmltest WHERE
xpath_exists('/myns:menu/myns:beers',data,ARRAY[ARRAY['myns','http://myns.com']]);
> + SELECT COUNT(id) FROM xmltest WHERE xpath_exists('/myns:menu/myns:beers/myns:name[text() =
''Molson'']',data,ARRAY[ARRAY['myns','http://myns.com']]);

>
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--
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Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Robert Haas
Date:
On Tue, Jul 27, 2010 at 7:33 PM, David Fetter <david@fetter.org> wrote:
>        Minor quibble with the regression tests: should we be using
>        dollar quotes in things like this?  Doubled-up quote marks:
>
>        SELECT xpath_exists('//town[text() =
''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
>
>        Dollar quote:
>
>        SELECT xpath_exists($$//town[text() =
'Cwmbran']$$,'<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);

Personally, I don't really see that as an improvement.  Dollar-quotes
are really nice for longer strings, or where you would otherwise have
quadrupled quotes (or more), but I don't see a big advantage to it
here.  Still, it's a question of opinion more than anything else.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Jeff Davis
Date:
On Tue, 2010-07-27 at 19:41 -0400, Robert Haas wrote:
> On Tue, Jul 27, 2010 at 7:33 PM, David Fetter <david@fetter.org> wrote:
> >        Minor quibble with the regression tests: should we be using
> >        dollar quotes in things like this?  Doubled-up quote marks:
> >
> >        SELECT xpath_exists('//town[text() =
''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
> >
> >        Dollar quote:
> >
> >        SELECT xpath_exists($$//town[text() =
'Cwmbran']$$,'<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
>
> Personally, I don't really see that as an improvement.  Dollar-quotes
> are really nice for longer strings, or where you would otherwise have
> quadrupled quotes (or more), but I don't see a big advantage to it
> here.  Still, it's a question of opinion more than anything else.

I like the idea of using dollar quotes, but I think they should be used
for both arguments (or neither). Using $$ for one and then shifting to
"'" for the second argument with no whitespace at all seems like the
least readable option.

Regards,
    Jeff Davis


Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Peter Eisentraut
Date:
On tis, 2010-07-27 at 16:33 -0700, David Fetter wrote:
> * Do we already have it?
>
>     Not really.  There are kludges to accomplish these things, but
>     they're available mostly in the sense that a general-purpose
>     language allows you to write code to do anything a Turing machine
>     can do.

I think this has been obsoleted by the xmlexists patch.


Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Mike Fowler
Date:
On 06/08/10 05:38, Peter Eisentraut wrote:
> On tis, 2010-07-27 at 16:33 -0700, David Fetter wrote:
>
>> * Do we already have it?
>>
>>      Not really.  There are kludges to accomplish these things, but
>>      they're available mostly in the sense that a general-purpose
>>      language allows you to write code to do anything a Turing machine
>>      can do.
>>
> I think this has been obsoleted by the xmlexists patch

In many ways yes. The only surviving difference is that xpath_exists has
support for namespaces and xmlexists does not as the grammar expects
namespaces to be handled in the xquery. So if people expect namespace
support to be useful that having both functions is useful until I (or
someone who works faster than me) get xquery going.

If the patch is to be committed, does it make sense for me to refine it
such that it uses the new xpath internal function you extracted in the
xmlexists patch?

Regards,

--
Mike Fowler
Registered Linux user: 379787


Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Peter Eisentraut
Date:
On fre, 2010-08-06 at 09:04 +0100, Mike Fowler wrote:
> If the patch is to be committed, does it make sense for me to refine
> it such that it uses the new xpath internal function you extracted in
> the xmlexists patch?

Yes, you can probably shrink this patch down to about 20 lines.


Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Mike Fowler
Date:
On 06/08/10 20:55, Peter Eisentraut wrote:
> On fre, 2010-08-06 at 09:04 +0100, Mike Fowler wrote:
>> If the patch is to be committed, does it make sense for me to refine
>> it such that it uses the new xpath internal function you extracted in
>> the xmlexists patch?
>
> Yes, you can probably shrink this patch down to about 20 lines.
>

Updated the patch so that it will apply to head and re-worked the
function to use the new xpath internal function.

Regards,

--
Mike Fowler
Registered Linux user: 379787

Attachment

Re: Review: Re: [PATCH] Re: [HACKERS] Adding xpath_exists function

From
Tom Lane
Date:
Mike Fowler <mike@mlfowler.com> writes:
> On 06/08/10 20:55, Peter Eisentraut wrote:
>> On fre, 2010-08-06 at 09:04 +0100, Mike Fowler wrote:
>>> If the patch is to be committed, does it make sense for me to refine
>>> it such that it uses the new xpath internal function you extracted in
>>> the xmlexists patch?
>>
>> Yes, you can probably shrink this patch down to about 20 lines.

> Updated the patch so that it will apply to head and re-worked the
> function to use the new xpath internal function.

Applied with minor corrections (improved docs, fixed regression tests,
adjusted OIDs for CVS HEAD).

            regards, tom lane