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>PostgreSQL 8.4.12 Documentation</TH
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>Appendix F. Additional Supplied Modules</TD
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><DIV
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><H1
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><A
NAME="XML2"
>F.38. xml2</A
></H1
><A
NAME="AEN120191"
></A
><P
> The <TT
CLASS="FILENAME"
>xml2</TT
> module provides XPath querying and
XSLT functionality.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN120195"
>F.38.1. Deprecation notice</A
></H2
><P
> From <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.3 on, there is XML-related
functionality based on the SQL/XML standard in the core server.
That functionality covers XML syntax checking and XPath queries,
which is what this module does, and more, but the API is
not at all compatible. It is planned that this module will be
removed in PostgreSQL 8.4 in favor of the newer standard API, so
you are encouraged to try converting your applications. If you
find that some of the functionality of this module is not
available in an adequate form with the newer API, please explain
your issue to pgsql-hackers@postgresql.org so that the deficiency
can be addressed.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN120199"
>F.38.2. Description of functions</A
></H2
><P
> <A
HREF="xml2.html#XML2-FUNCTIONS-TABLE"
>Table F-35</A
> shows the functions provided by this module.
These functions provide straightforward XML parsing and XPath queries.
All arguments are of type <TT
CLASS="TYPE"
>text</TT
>, so for brevity that is not shown.
</P
><DIV
CLASS="TABLE"
><A
NAME="XML2-FUNCTIONS-TABLE"
></A
><P
><B
>Table F-35. Functions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><TBODY
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xml_is_well_formed(document) returns bool
</PRE
>
</TD
><TD
> <P
> This parses the document text in its parameter and returns true if the
document is well-formed XML. (Note: before PostgreSQL 8.2, this
function was called <CODE
CLASS="FUNCTION"
>xml_valid()</CODE
>. That is the wrong name
since validity and well-formedness have different meanings in XML.
The old name is still available, but is deprecated.)
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_string(document,query) returns text
xpath_number(document,query) returns float4
xpath_bool(document,query) returns bool
</PRE
>
</TD
><TD
> <P
> These functions evaluate the XPath query on the supplied document, and
cast the result to the specified type.
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_nodeset(document,query,toptag,itemtag) returns text
</PRE
>
</TD
><TD
> <P
> This evaluates query on document and wraps the result in XML tags. If
the result is multivalued, the output will look like:
</P
>
<TT
CLASS="LITERAL"
> <toptag>
<itemtag>Value 1 which could be an XML fragment</itemtag>
<itemtag>Value 2....</itemtag>
</toptag>
</TT
>
<P
> If either toptag or itemtag is an empty string, the relevant tag is omitted.
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_nodeset(document,query) returns text
</PRE
>
</TD
><TD
> <P
> Like xpath_nodeset(document,query,toptag,itemtag) but result omits both tags.
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_nodeset(document,query,itemtag) returns text
</PRE
>
</TD
><TD
> <P
> Like xpath_nodeset(document,query,toptag,itemtag) but result omits toptag.
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_list(document,query,separator) returns text
</PRE
>
</TD
><TD
> <P
> This function returns multiple values separated by the specified
separator, for example <TT
CLASS="LITERAL"
>Value 1,Value 2,Value 3</TT
> if
separator is <TT
CLASS="LITERAL"
>,</TT
>.
</P
>
</TD
></TR
><TR
><TD
> <PRE
CLASS="SYNOPSIS"
> xpath_list(document,query) returns text
</PRE
>
</TD
><TD
> This is a wrapper for the above function that uses <TT
CLASS="LITERAL"
>,</TT
>
as the separator.
</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN120248"
>F.38.3. <TT
CLASS="LITERAL"
>xpath_table</TT
></A
></H2
><PRE
CLASS="SYNOPSIS"
> xpath_table(text key, text document, text relation, text xpaths, text criteria) returns setof record
</PRE
><P
> <CODE
CLASS="FUNCTION"
>xpath_table</CODE
> is a table function that evaluates a set of XPath
queries on each of a set of documents and returns the results as a
table. The primary key field from the original document table is returned
as the first column of the result so that the result set
can readily be used in joins.
</P
><DIV
CLASS="TABLE"
><A
NAME="AEN120254"
></A
><P
><B
>Table F-36. Parameters</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><TBODY
><TR
><TD
><TT
CLASS="PARAMETER"
>key</TT
></TD
><TD
> <P
> the name of the <SPAN
CLASS="QUOTE"
>"key"</SPAN
> field — this is just a field to be used as
the first column of the output table, i.e., it identifies the record from
which each output row came (see note below about multiple values)
</P
>
</TD
></TR
><TR
><TD
><TT
CLASS="PARAMETER"
>document</TT
></TD
><TD
> <P
> the name of the field containing the XML document
</P
>
</TD
></TR
><TR
><TD
><TT
CLASS="PARAMETER"
>relation</TT
></TD
><TD
> <P
> the name of the table or view containing the documents
</P
>
</TD
></TR
><TR
><TD
><TT
CLASS="PARAMETER"
>xpaths</TT
></TD
><TD
> <P
> one or more XPath expressions, separated by <TT
CLASS="LITERAL"
>|</TT
>
</P
>
</TD
></TR
><TR
><TD
><TT
CLASS="PARAMETER"
>criteria</TT
></TD
><TD
> <P
> the contents of the WHERE clause. This cannot be omitted, so use
<TT
CLASS="LITERAL"
>true</TT
> or <TT
CLASS="LITERAL"
>1=1</TT
> if you want to
process all the rows in the relation
</P
>
</TD
></TR
></TBODY
></TABLE
></DIV
><P
> These parameters (except the XPath strings) are just substituted
into a plain SQL SELECT statement, so you have some flexibility — the
statement is
</P
><P
> <TT
CLASS="LITERAL"
> SELECT <key>, <document> FROM <relation> WHERE <criteria>
</TT
>
</P
><P
> so those parameters can be <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>anything</I
></SPAN
> valid in those particular
locations. The result from this SELECT needs to return exactly two
columns (which it will unless you try to list multiple fields for key
or document). Beware that this simplistic approach requires that you
validate any user-supplied values to avoid SQL injection attacks.
</P
><P
> The function has to be used in a <TT
CLASS="LITERAL"
>FROM</TT
> expression, with an
<TT
CLASS="LITERAL"
>AS</TT
> clause to specify the output columns; for example
</P
><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM
xpath_table('article_id',
'article_xml',
'articles',
'/article/author|/article/pages|/article/title',
'date_entered > ''2003-01-01'' ')
AS t(article_id integer, author text, page_count integer, title text);
</PRE
><P
> The <TT
CLASS="LITERAL"
>AS</TT
> clause defines the names and types of the columns in the
output table. The first is the <SPAN
CLASS="QUOTE"
>"key"</SPAN
> field and the rest correspond
to the XPath queries.
If there are more XPath queries than result columns,
the extra queries will be ignored. If there are more result columns
than XPath queries, the extra columns will be NULL.
</P
><P
> Notice that this example defines the <TT
CLASS="STRUCTNAME"
>page_count</TT
> result
column as an integer. The function deals internally with string
representations, so when you say you want an integer in the output, it will
take the string representation of the XPath result and use PostgreSQL input
functions to transform it into an integer (or whatever type the <TT
CLASS="TYPE"
>AS</TT
>
clause requests). An error will result if it can't do this — for
example if the result is empty — so you may wish to just stick to
<TT
CLASS="TYPE"
>text</TT
> as the column type if you think your data has any problems.
</P
><P
> The calling <TT
CLASS="COMMAND"
>SELECT</TT
> statement doesn't necessarily have be
be just <TT
CLASS="LITERAL"
>SELECT *</TT
> — it can reference the output
columns by name or join them to other tables. The function produces a
virtual table with which you can perform any operation you wish (e.g.
aggregation, joining, sorting etc). So we could also have:
</P
><PRE
CLASS="PROGRAMLISTING"
>SELECT t.title, p.fullname, p.email
FROM xpath_table('article_id', 'article_xml', 'articles',
'/article/title|/article/author/@id',
'xpath_string(article_xml,''/article/@date'') > ''2003-03-20'' ')
AS t(article_id integer, title text, author_id integer),
tblPeopleInfo AS p
WHERE t.author_id = p.person_id;
</PRE
><P
> as a more complicated example. Of course, you could wrap all
of this in a view for convenience.
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN120308"
>F.38.3.1. Multivalued results</A
></H3
><P
> The <CODE
CLASS="FUNCTION"
>xpath_table</CODE
> function assumes that the results of each XPath query
might be multi-valued, so the number of rows returned by the function
may not be the same as the number of input documents. The first row
returned contains the first result from each query, the second row the
second result from each query. If one of the queries has fewer values
than the others, NULLs will be returned instead.
</P
><P
> In some cases, a user will know that a given XPath query will return
only a single result (perhaps a unique document identifier) — if used
alongside an XPath query returning multiple results, the single-valued
result will appear only on the first row of the result. The solution
to this is to use the key field as part of a join against a simpler
XPath query. As an example:
</P
><PRE
CLASS="PROGRAMLISTING"
> CREATE TABLE test (
id int4 NOT NULL,
xml text,
CONSTRAINT pk PRIMARY KEY (id)
);
INSERT INTO test VALUES (1, '<doc num="C1">
<line num="L1"><a>1</a><b>2</b><c>3</c></line>
<line num="L2"><a>11</a><b>22</b><c>33</c></line>
</doc>');
INSERT INTO test VALUES (2, '<doc num="C2">
<line num="L1"><a>111</a><b>222</b><c>333</c></line>
<line num="L2"><a>111</a><b>222</b><c>333</c></line>
</doc>');
SELECT * FROM
xpath_table('id','xml','test',
'/doc/@num|/doc/line/@num|/doc/line/a|/doc/line/b|/doc/line/c',
'true')
AS t(id int4, doc_num varchar(10), line_num varchar(10), val1 int4, val2 int4, val3 int4)
WHERE id = 1 ORDER BY doc_num, line_num
id | doc_num | line_num | val1 | val2 | val3
----+---------+----------+------+------+------
1 | C1 | L1 | 1 | 2 | 3
1 | | L2 | 11 | 22 | 33
</PRE
><P
> To get doc_num on every line, the solution is to use two invocations
of xpath_table and join the results:
</P
><PRE
CLASS="PROGRAMLISTING"
> SELECT t.*,i.doc_num FROM
xpath_table('id', 'xml', 'test',
'/doc/line/@num|/doc/line/a|/doc/line/b|/doc/line/c',
'true')
AS t(id int4, line_num varchar(10), val1 int4, val2 int4, val3 int4),
xpath_table('id', 'xml', 'test', '/doc/@num', 'true')
AS i(id int4, doc_num varchar(10))
WHERE i.id=t.id AND i.id=1
ORDER BY doc_num, line_num;
id | line_num | val1 | val2 | val3 | doc_num
----+----------+------+------+------+---------
1 | L1 | 1 | 2 | 3 | C1
1 | L2 | 11 | 22 | 33 | C1
(2 rows)
</PRE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN120316"
>F.38.4. XSLT functions</A
></H2
><P
> The following functions are available if libxslt is installed:
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN120319"
>F.38.4.1. <TT
CLASS="LITERAL"
>xslt_process</TT
></A
></H3
><PRE
CLASS="SYNOPSIS"
> xslt_process(text document, text stylesheet, text paramlist) returns text
</PRE
><P
> This function applies the XSL stylesheet to the document and returns
the transformed result. The paramlist is a list of parameter
assignments to be used in the transformation, specified in the form
<TT
CLASS="LITERAL"
>a=1,b=2</TT
>. Note that the
parameter parsing is very simple-minded: parameter values cannot
contain commas!
</P
><P
> Also note that if either the document or stylesheet values do not
begin with a < then they will be treated as URLs and libxslt will
fetch them. It follows that you can use <CODE
CLASS="FUNCTION"
>xslt_process</CODE
> as a
means to fetch the contents of URLs — you should be aware of the
security implications of this.
</P
><P
> There is also a two-parameter version of <CODE
CLASS="FUNCTION"
>xslt_process</CODE
> which
does not pass any parameters to the transformation.
</P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN120329"
>F.38.5. Author</A
></H2
><P
> John Gray <CODE
CLASS="EMAIL"
><<A
HREF="mailto:jgray@azuli.co.uk"
>jgray@azuli.co.uk</A
>></CODE
>
</P
><P
> Development of this module was sponsored by Torchbox Ltd. (www.torchbox.com).
It has the same BSD licence as PostgreSQL.
</P
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