Re: Add XMLNamespaces to XMLElement - Mailing list pgsql-hackers

Hi,
+1 for the enhancement.

I haven't compiled and reviewed the full patch yet, please see a few
comments from my side based on static analysis.

1. Though changes are targeted for XMLNAMESPACES for XMLElement but in
my opinion it will affect XMLTABLE as well because the
'xml_namespace_list' rule is shared now.
Adding 'NO DEFAULT' in xml_namespace_list will allow users to use it
with XMLTABLE XMLNAMESPACES as well.PostgreSQL grammar allow to
specify DEFAULT in NAMESPACE but resulting in following error:
"ERROR:  DEFAULT namespace is not supported"
What would be behavior with this change for XMLTABLE, should this be
allowed and the error messages need to be updated (may be this will
not be an error at all) or we need to restrict users to not use 'NO
DEFAULT' with XMLTable.

2. Should we reuse the 'xml_namespaces' rule for XMLTable, as the
definition is the same.

3. In this patch 'NO DEFAULT' behavior is like DEFAULT '<blank>'
(empty uri) , should not it be more like 'DEFAULT NULL' to result in
the following ?
SELECT xmlelement(NAME "root", xmlnamespaces(NO DEFAULT));
    xmlelement
------------------
<root/>

instead of

SELECT xmlelement(NAME "root", xmlnamespaces(NO DEFAULT));
    xmlelement
------------------
<root xmlns=""/>

Regards
Umar Hayat

On Sat, 21 Dec 2024 at 14:57, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>
> Hi
>
> so 21. 12. 2024 v 0:51 odesílatel Jim Jones <jim.jones@uni-muenster.de> napsal:
>>
>> Hi,
>>
>> I'd like to propose the implementation of the XMLNamespaces option for
>> XMLElement.
>>
>> XMLNAMESPACES(nsuri AS nsprefix)
>> XMLNAMESPACES(DEFAULT default-nsuri)
>> XMLNAMESPACES(NO DEFAULT)
>>
>> * nsprefix:              Namespace's prefix.
>> * nsuri:                 Namespace's URI.
>> * DEFAULT default-nsuri: Specifies the DEFAULT namespace to use within
>> the scope of a namespace declaration.
>> * NO DEFAULT:            Specifies that NO DEFAULT namespace is to be
>> used within the scope of a namespace declaration.
>>
>> This basically works pretty much like XMLAttributes, but with a few more
>> restrictions (see SQL/XML:2023, 11.2 <XML lexically scoped options>):
>>
>> * XML namespace declaration shall contain at most one DEFAULT namespace
>> declaration item.
>> * No namespace prefix shall be equivalent to xml or xmlns.
>> * No namespace URI shall be identical to http://www.w3.org/2000/xmlns/
>> or to http://www.w3.org/XML/1998/namespace.
>> * The value of a namespace URI contained in an regular namespace
>> declaration item (no DEFAULT) shall not be a zero-length string.
>>
>> Examples:
>>
>> SELECT xmlelement(NAME "foo", xmlnamespaces('http://x.y' AS bar));
>>           xmlelement
>> -------------------------------
>>  <foo xmlns:bar="http://x.y"/>
>>
>> SELECT xmlelement(NAME "foo", xmlnamespaces(DEFAULT 'http://x.y'));
>>         xmlelement
>> ---------------------------
>>  <foo xmlns="http://x.y"/>
>>
>> SELECT xmlelement(NAME "foo", xmlnamespaces(NO DEFAULT));
>>    xmlelement
>> -----------------
>>  <foo xmlns=""/>
>>
>> In transformXmlExpr() it seemed convenient to use the same parameters to
>> store the prefixes and URIs as in XMLAttributes (arg_names and
>> named_args), but I am still not so sure it is the right approach. Is
>> there perhaps a better way?
>>
>> Any thoughts? Feedback welcome!
>
>
> +1
>
> Pavel
>>
>>
>> Best, Jim



--
Umar Hayat
Bitnine (https://bitnine.net/)