Re: BUG #8469: Xpath behaviour unintuitive / arguably wrong

On 10/02/2013 06:19 PM, Bruce Momjian wrote:
> On Tue, Sep 24, 2013 at 06:43:19PM +0000, dennis(dot)noordsij(at)helsinki(dot)fi wrote:
>> The following bug has been logged on the website:
>>
>> Bug reference: 8469
>> Logged by: Dennis
>> Email address: dennis(dot)noordsij(at)helsinki(dot)fi
>> PostgreSQL version: 9.3.0
>> Operating system: FreeBSD 9.2-RC4
>> Description:
>>
>> Hi,
>>
>>
>> After upgrading an 8.1 version to 9.3.0 I am suddenly seeing text fields
>> containing "&" where they are populated from XML. This may be a
>> coincidence and the problem may have existed earlier, in any case, now I
>> noticed.
>>
>>
>> I extract the text content of XML nodes using xpath, from something like:
>>
>>
>> <name>Jones &amp; Smith</name>
>>
>>
>> The reason I end up with "&amp;" is the IMHO rather odd xpath behaviour:
>>
>>
>> # select xpath('/a/text()', (select xmlelement(name "a", 'A & B')));
>>
>>
>> xpath
>> ---------------
>> {"A &amp; B"}
>>
>>
>> The canonical contents of "a" is "A & B". At first search I've found some
>> rather heated debates about this with bits of name calling; I certainly do
>> not want to get into that and I apologize in advance to those who feel very
>> strongly about this.
>>
>>
>> I've seen one "fix" describe the problem as:
>>
>>
>> ""DESCRIPTION: Submitter invokes following statement:
>> SELECT (XPATH('/*/text()', '<root>&lt;</root>'))[1].
>> He expect (escaped) result "&lt;", but gets "<"
>> """
>>
>>
>> With respect, this "bug" makes no sense as this produces in fact the right
>> result. The actual value of <root> is "<", it's just escaped when serialized
>> to XML. If <root> were to actually contain "&lt;", it'd be serialized as
>> "&amp;lt;". It should not be possible to be blindly cast to a text type, but
>> explicitly serialized as such.
>>
>>
>> At least the reviewer at:
>>
>>
>> http://www.postgresql.org/message-id/201106291934.23089.rsmogura@softperience.eu
>
> There are two other similar bug reports on this from February and March
> of this year:
>
> http://www.postgresql.org/message-id/E1U1FKL-0002rD-RO@wrihigleys.postgresql.org

I think that should be:
http://www.postgresql.org/message-id/E1U1FKL-0002rD-RO@wrigleys.postgresql.org

> http://www.postgresql.org/message-id/E1UHyUw-0001oj-HE@wrigleys.postgresql.org
>
> Someone who knows XML needs to take leadership on this and propose a
> patch.

agreed

Stefan