Re: [PATCH] Add CANONICAL option to xmlserialize

On 29.08.24 20:50, Pavel Stehule wrote:
>
> I know, but theoretically, there can be some benefit for CANONICAL if
> pg supports bytea there. Lot of databases still use non utf8 encoding.
>
> It is a more theoretical question - if pg supports different types
> there in future  (because SQL/XML or Oracle), then CANONICAL can be
> used without limit,
I like the idea of extending the feature to support bytea. I can
definitely take a look at it, but perhaps in another patch? This change
would most likely involve transformXmlSerialize in parse_expr.c, and I'm
not sure of the impact in other usages of XMLSERIALIZE.
> or CANONICAL can be used just for text? And you are sure, so you can
> compare text X text, instead xml X xml?
Yes, currently it only supports varchar or text - and their cousins. The
idea is to format the xml and serialize it as text in a way that they
can compared based on their content, independently of how they were
written, e.g '<foo a="1" b="2"/>' is equal to '<foo b="2" a="1"/>'.

>
> +SELECT xmlserialize(CONTENT doc AS text CANONICAL) =
> xmlserialize(CONTENT doc AS text CANONICAL WITH COMMENTS) FROM
> xmltest_serialize;
> + ?column?
> +----------
> + t
> + t
> +(2 rows)
>
> Maybe I am a little bit confused by these regress tests, because at
> the end it is not too useful - you compare two identical XML, and WITH
> COMMENTS and WITHOUT COMMENTS is tested elsewhere. I tried to search
> for a sense of this test.  Better to use really different documents
> (columns) instead.

Yeah, I can see that it's confusing. In this example I actually just
wanted to test that the default option of CANONICAL is CANONICAL WITH
COMMENTS, even if you don't mention it. In the docs I mentioned it like
this:

"The optional parameters WITH COMMENTS (which is the default) or WITH NO
COMMENTS, respectively, keep or remove XML comments from the given
document."

Perhaps I should rephrase it? Or maybe a comment in the regression tests
would suffice?

Thanks a lot for the input!

--
Jim