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Diffstat (limited to 'doc/src/sgml/xml2.sgml')
| -rw-r--r-- | doc/src/sgml/xml2.sgml | 388 |
1 files changed, 189 insertions, 199 deletions
diff --git a/doc/src/sgml/xml2.sgml b/doc/src/sgml/xml2.sgml index 9a0af4b537f..96f8b18d876 100644 --- a/doc/src/sgml/xml2.sgml +++ b/doc/src/sgml/xml2.sgml @@ -1,31 +1,41 @@ +<!-- $PostgreSQL: pgsql/doc/src/sgml/xml2.sgml,v 1.4 2007/12/06 04:12:10 tgl Exp $ --> + <sect1 id="xml2"> - <title>xml2: XML-handling functions</title> - + <title>xml2</title> + <indexterm zone="xml2"> <primary>xml2</primary> </indexterm> + <para> + The <filename>xml2</> module provides XPath querying and + XSLT functionality. + </para> + <sect2> <title>Deprecation notice</title> + <para> - From PostgreSQL 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 as well, 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. + From <productname>PostgreSQL</> 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. </para> </sect2> - + <sect2> <title>Description of functions</title> + <para> - The first set of functions are straightforward XML parsing and XPath queries: + These functions provide straightforward XML parsing and XPath queries. + All arguments are of type <type>text</>, so for brevity that is not shown. </para> <table> @@ -34,27 +44,27 @@ <tbody> <row> <entry> - <programlisting> - xml_is_well_formed(document) RETURNS bool - </programlisting> + <synopsis> + xml_is_well_formed(document) returns bool + </synopsis> </entry> <entry> <para> 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 xml_valid(). That is the wrong name since validity and - well-formedness have different meanings in XML. The old name is still - available, but is deprecated and will be removed in 8.3.) + document is well-formed XML. (Note: before PostgreSQL 8.2, this + function was called <function>xml_valid()</>. That is the wrong name + since validity and well-formedness have different meanings in XML. + The old name is still available, but is deprecated.) </para> </entry> </row> <row> <entry> - <programlisting> - xpath_string(document,query) RETURNS text - xpath_number(document,query) RETURNS float4 - xpath_bool(document,query) RETURNS bool - </programlisting> + <synopsis> + xpath_string(document,query) returns text + xpath_number(document,query) returns float4 + xpath_bool(document,query) returns bool + </synopsis> </entry> <entry> <para> @@ -65,9 +75,9 @@ </row> <row> <entry> - <programlisting> - xpath_nodeset(document,query,toptag,itemtag) RETURNS text - </programlisting> + <synopsis> + xpath_nodeset(document,query,toptag,itemtag) returns text + </synopsis> </entry> <entry> <para> @@ -75,10 +85,10 @@ the result is multivalued, the output will look like: </para> <literal> - <toptag> - <itemtag>Value 1 which could be an XML fragment</itemtag> - <itemtag>Value 2....</itemtag> - </toptag> + <toptag> + <itemtag>Value 1 which could be an XML fragment</itemtag> + <itemtag>Value 2....</itemtag> + </toptag> </literal> <para> If either toptag or itemtag is an empty string, the relevant tag is omitted. @@ -87,49 +97,51 @@ </row> <row> <entry> - <programlisting> - xpath_nodeset(document,query) RETURNS - </programlisting> + <synopsis> + xpath_nodeset(document,query) returns text + </synopsis> </entry> <entry> <para> - Like xpath_nodeset(document,query,toptag,itemtag) but text omits both tags. + Like xpath_nodeset(document,query,toptag,itemtag) but result omits both tags. </para> </entry> </row> <row> <entry> - <programlisting> - xpath_nodeset(document,query,itemtag) RETURNS - </programlisting> + <synopsis> + xpath_nodeset(document,query,itemtag) returns text + </synopsis> </entry> <entry> <para> - Like xpath_nodeset(document,query,toptag,itemtag) but text omits toptag. + Like xpath_nodeset(document,query,toptag,itemtag) but result omits toptag. </para> </entry> </row> <row> <entry> - <programlisting> - xpath_list(document,query,seperator) RETURNS text - </programlisting> + <synopsis> + xpath_list(document,query,separator) returns text + </synopsis> </entry> <entry> <para> - This function returns multiple values seperated by the specified - seperator, e.g. Value 1,Value 2,Value 3 if seperator=','. + This function returns multiple values separated by the specified + separator, for example <literal>Value 1,Value 2,Value 3</> if + separator is <literal>,</>. </para> </entry> </row> <row> <entry> - <programlisting> - xpath_list(document,query) RETURNS text - </programlisting> + <synopsis> + xpath_list(document,query) returns text + </synopsis> </entry> <entry> - This is a wrapper for the above function that uses ',' as the seperator. + This is a wrapper for the above function that uses <literal>,</> + as the separator. </entry> </row> </tbody> @@ -137,38 +149,37 @@ </table> </sect2> - <sect2> <title><literal>xpath_table</literal></title> + + <synopsis> + xpath_table(text key, text document, text relation, text xpaths, text criteria) returns setof record + </synopsis> + <para> - This is a table function which 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 resultset from xpath_table can - be readily used in joins. - </para> - <para> - The function itself takes 5 arguments, all text. + <function>xpath_table</> 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. </para> - <programlisting> - xpath_table(key,document,relation,xpaths,criteria) - </programlisting> + <table> <title>Parameters</title> <tgroup cols="2"> <tbody> <row> - <entry><literal>key</literal></entry> + <entry><parameter>key</parameter></entry> <entry> <para> - the name of the "key" 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). + the name of the <quote>key</> 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) </para> </entry> </row> <row> - <entry><literal>document</literal></entry> + <entry><parameter>document</parameter></entry> <entry> <para> the name of the field containing the XML document @@ -176,7 +187,7 @@ </entry> </row> <row> - <entry><literal>relation</literal></entry> + <entry><parameter>relation</parameter></entry> <entry> <para> the name of the table or view containing the documents @@ -184,20 +195,20 @@ </entry> </row> <row> - <entry><literal>xpaths</literal></entry> + <entry><parameter>xpaths</parameter></entry> <entry> <para> - multiple xpath expressions separated by <literal>|</literal> + one or more XPath expressions, separated by <literal>|</literal> </para> </entry> </row> <row> - <entry><literal>criteria</literal></entry> + <entry><parameter>criteria</parameter></entry> <entry> <para> - The contents of the where clause. This needs to be specified, - so use "true" or "1=1" here if you want to process all the rows in the - relation. + the contents of the WHERE clause. This cannot be omitted, so use + <literal>true</literal> or <literal>1=1</literal> if you want to + process all the rows in the relation </para> </entry> </row> @@ -206,75 +217,75 @@ </table> <para> - NB These parameters (except the XPath strings) are just substituted - into a plain SQL SELECT statement, so you have some flexibility - the + These parameters (except the XPath strings) are just substituted + into a plain SQL SELECT statement, so you have some flexibility — the statement is </para> <para> <literal> - SELECT <key>,<document> FROM <relation> WHERE <criteria> + SELECT <key>, <document> FROM <relation> WHERE <criteria> </literal> </para> <para> - so those parameters can be *anything* valid in those particular + so those parameters can be <emphasis>anything</> 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. </para> - - <para> - Using the function - </para> - + <para> - The function has to be used in a FROM expression. This gives the following - form: + The function has to be used in a <literal>FROM</> expression, with an + <literal>AS</> clause to specify the output columns; for example </para> - + <programlisting> SELECT * FROM -xpath_table('article_id', - 'article_xml', - 'articles', - '/article/author|/article/pages|/article/title', - 'date_entered > ''2003-01-01'' ') +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); </programlisting> <para> - The AS clause defines the names and types of the columns in the - virtual table. If there are more XPath queries than result columns, + The <literal>AS</> clause defines the names and types of the columns in the + output table. The first is the <quote>key</> 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. </para> <para> - Note that I've said in this example that pages is 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 AS 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 'text' as the - column type if you think your data has any problems. + Notice that this example defines the <structname>page_count</> 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 <type>AS</> + 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 + <type>text</> as the column type if you think your data has any problems. </para> + <para> - The select statement doesn't need to use * alone - it can reference the + The calling <command>SELECT</> statement doesn't necessarily have be + be just <literal>SELECT *</> — 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: </para> <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 +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; </programlisting> @@ -282,91 +293,74 @@ WHERE t.author_id = p.person_id; as a more complicated example. Of course, you could wrap all of this in a view for convenience. </para> + <sect3> <title>Multivalued results</title> + <para> - The xpath_table function assumes that the results of each XPath query + The <function>xpath_table</> 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. </para> + <para> 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 + 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: </para> - - <para> - <literal> - CREATE TABLE test - ( - id int4 NOT NULL, - xml text, - CONSTRAINT pk PRIMARY KEY (id) - ) - WITHOUT OIDS; - - 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>'); - </literal> - </para> - </sect3> - - <sect3> - <title>The query</title> - - <programlisting> - SELECT * FROM xpath_table('id','xml','test', - '/doc/@num|/doc/line/@num|/doc/line/a|/doc/line/b|/doc/line/c','1=1') - 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 - </programlisting> - - <para> - Gives the result: - </para> - + <programlisting> - id | doc_num | line_num | val1 | val2 | val3 - ----+---------+----------+------+------+------ - 1 | C1 | L1 | 1 | 2 | 3 - 1 | | L2 | 11 | 22 | 33 + 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 </programlisting> - + <para> - To get doc_num on every line, the solution is to use two invocations - of xpath_table and join the results: + To get doc_num on every line, the solution is to use two invocations + of xpath_table and join the results: </para> - + <programlisting> - SELECT t.*,i.doc_num FROM - xpath_table('id','xml','test', - '/doc/line/@num|/doc/line/a|/doc/line/b|/doc/line/c','1=1') - AS t(id int4, line_num varchar(10), val1 int4, val2 int4, val3 int4), - xpath_table('id','xml','test','/doc/@num','1=1') - AS i(id int4, doc_num varchar(10)) + 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; - </programlisting> - - <para> - which gives the desired result: - </para> - - <programlisting> + id | line_num | val1 | val2 | val3 | doc_num ----+----------+------+------+------+--------- 1 | L1 | 1 | 2 | 3 | C1 @@ -375,62 +369,58 @@ WHERE t.author_id = p.person_id; </programlisting> </sect3> </sect2> - <sect2> <title>XSLT functions</title> + <para> The following functions are available if libxslt is installed (this is not currently detected automatically, so you will have to amend the - Makefile) + Makefile): </para> <sect3> <title><literal>xslt_process</literal></title> - <programlisting> - xslt_process(document,stylesheet,paramlist) RETURNS text - </programlisting> + + <synopsis> + xslt_process(text document, text stylesheet, text paramlist) returns text + </synopsis> <para> This function appplies 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 - 'a=1,b=2'. Note that this is also proof-of-concept code and the - parameter parsing is very simple-minded (e.g. parameter values cannot - contain commas!) + <literal>a=1,b=2</>. Note that the + parameter parsing is very simple-minded: parameter values cannot + contain commas! </para> + <para> 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 thus follows that you can use xslt_process as a means - to fetch the contents of URLs - you should be aware of the security - implications of this. - </para> + fetch them. It follows that you can use <function>xslt_process</> as a + means to fetch the contents of URLs — you should be aware of the + security implications of this. + </para> + <para> - There is also a two-parameter version of xslt_process which does not - pass any parameters to the transformation. + There is also a two-parameter version of <function>xslt_process</> which + does not pass any parameters to the transformation. </para> </sect3> </sect2> <sect2> - <title>Credits</title> - <para> - Development of this module was sponsored by Torchbox Ltd. (www.torchbox.com) - It has the same BSD licence as PostgreSQL. - </para> + <title>Author</title> + <para> - This version of the XML functions provides both XPath querying and - XSLT functionality. There is also a new table function which allows - the straightforward return of multiple XML results. Note that the current code - doesn't take any particular care over character sets - this is - something that should be fixed at some point! + John Gray <email>jgray@azuli.co.uk</email> </para> + <para> - If you have any comments or suggestions, please do contact me at - <email>jgray@azuli.co.uk.</email> Unfortunately, this isn't my main job, so - I can't guarantee a rapid response to your query! + Development of this module was sponsored by Torchbox Ltd. (www.torchbox.com). + It has the same BSD licence as PostgreSQL. </para> </sect2> -</sect1> +</sect1> |