Re: patch: function xmltable

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: patch: function xmltable
Date: 2016-11-24 05:18:31
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2016-11-24 5:52 GMT+01:00 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:

> Hi
> 2016-11-24 0:13 GMT+01:00 Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>:
>> Oh my, I just noticed we have a new xpath preprocessor in this patch
>> too. Where did this code come from -- did you write it all from
>> scratch?
> I wrote it from scratch - libxml2 has not any API for iteration over XPath
> expression (different than iteration over XPath expression result), and
> what I have info, there will not be any new API in libxml2.
> There are two purposes:
> Safe manipulation with XPath expression prefixes - ANSI SQL design
> implicitly expects some prefix, but it can be used manually. The prefix
> should not be used twice and in some situations, when it can breaks the
> expression.

Implicit prefix for column PATH expressions is "./". An user can use it

In my initial patches, the manipulations with XPath expression was more
complex - now, it can be reduced - but then we lost default namespaces
support, what is nice feature, supported other providers.

> Second goal is support default namespaces - when we needed parser for
> first task, then the enhancing for this task was not too much lines more.
> This parser can be used for enhancing current XPath function - default
> namespaces are pretty nice, when you have to use namespaces.
>> --
>> Álvaro Herrera
>> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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