如何为Postgresql数据库全文搜索(full text search)编写解析器(parser)

用英文写的，主要是命令和代码，就不翻译了，偷懒一下。

This article show you how to create a parser to handle camel case [3] in string in Postgresql full text search. This parser is tested on Postgresql 8.3.9 version. The OS is ubuntu 8.10.

[1,2] will give you basic background and sample for old version. I update the code to fit 8.3.9 version, especial lots of changes in the SQL statement.

Create parser

First, create a directory for put all files, for example: /home/user/Desktop/test_parser

Create file "test_parser.c". I use vim.

#include "postgres.h"


#include "utils/builtins.h"






#ifdef PG_MODULE_MAGIC


PG_MODULE_MAGIC;


#endif




/*


* types


*/




/* self-defined type */


typedef struct {


char * buffer; /* text to parse */


int len; /* length of the text in buffer */


int pos; /* position of the parser */


} ParserState;




/* copy-paste from wparser.h of tsearch2 */


typedef struct {


int lexid;


char *alias;


char *descr;


} LexDescr;




/*


* prototypes


*/


PG_FUNCTION_INFO_V1(testprs_start);


Datum testprs_start(PG_FUNCTION_ARGS);




PG_FUNCTION_INFO_V1(testprs_getlexeme);


Datum testprs_getlexeme(PG_FUNCTION_ARGS);




PG_FUNCTION_INFO_V1(testprs_end);


Datum testprs_end(PG_FUNCTION_ARGS);




PG_FUNCTION_INFO_V1(testprs_lextype);


Datum testprs_lextype(PG_FUNCTION_ARGS);




/*


* functions


*/


Datum testprs_start


(PG_FUNCTION_ARGS)


{


ParserState *pst = (ParserState *) palloc(sizeof(ParserState));


pst->buffer = (char *) PG_GETARG_POINTER(0);


pst->len = PG_GETARG_INT32(1);


pst->pos = 0;


PG_RETURN_POINTER(pst);


}




Datum testprs_getlexeme


(PG_FUNCTION_ARGS)


{


ParserState *pst = (ParserState *) PG_GETARG_POINTER(0);


char **t = (char **) PG_GETARG_POINTER(1);


int *tlen = (int *) PG_GETARG_POINTER(2);


int type;




*tlen = pst->pos;


*t = pst->buffer + pst->pos;




HTML clipboard/* main process here */


 if (((pst->buffer)[pst->pos] >= 'A' && (pst->buffer)[pst->pos] <= 'Z') && 
(pst->pos < pst->len)) {


/* word type */


type = 3;


(pst->pos)++;


/* for case like: ItemURL => Item URL*/


if(((pst->buffer)[pst->pos] >= 'A' && (pst->buffer)[pst->pos] <= 'Z') && (pst->pos 
< pst->len)){


while (((pst->buffer)[pst->pos] >= 'A' && (pst->buffer)[pst->pos] <= 'Z') 
&& (pst->pos < pst->len)) {


(pst->pos)++;


}


}



/* go to the next upper case character */


while (((pst->buffer)[pst->pos] >= 'a' && (pst->buffer)[pst->pos] <= 'z') 
&& (pst->pos < pst->len)) {


(pst->pos)++;


}


} 



if (((pst->buffer)[pst->pos] >= 'a' && (pst->buffer)[pst->pos] <= 'z') && 
(pst->pos < pst->len)) {


/* word type */


type = 3;


(pst->pos)++;


/* go to the next upper case character */


while (((pst->buffer)[pst->pos] >= 'a' && (pst->buffer)[pst->pos] <= 'z') 
&& (pst->pos < pst->len)) {


(pst->pos)++;


}


}




*tlen = pst->pos - *tlen;




/* we are finished if (*tlen == 0) */


if (*tlen == 0) type=0;


PG_RETURN_INT32(type);


}




Datum testprs_end


(PG_FUNCTION_ARGS)


{


ParserState *pst = (ParserState *) PG_GETARG_POINTER(0);


pfree(pst);


PG_RETURN_VOID();


}




Datum testprs_lextype


(PG_FUNCTION_ARGS)


{


/*


Remarks:


- we have to return the blanks for headline reason


- we use the same lexids like Teodor in the default


word parser; in this way we can reuse the headline


function of the default word parser.


*/


LexDescr *descr = (LexDescr *) palloc(sizeof(LexDescr) * (2+1));




/* there are only two types in this parser */


descr[0].lexid = 3;


descr[0].alias = pstrdup("word");


descr[0].descr = pstrdup("Word");


descr[1].lexid = 12;


descr[1].alias = pstrdup("blank");


descr[1].descr = pstrdup("Space symbols");


descr[2].lexid = 0;


PG_RETURN_POINTER(descr);


}

Create "Makefile" file under the same directory.

override CPPFLAGS := -I. $(CPPFLAGS)
MODULE_big = test_parser
OBJS = test_parser.o

DATA_built = test_parser.sql
DATA =
REGRESS = test_parser

ifdef USE_PGXS
PGXS := $(shell pg_config --pgxs)
include $(PGXS)
else
subdir = contrib/test_parser
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

Create "test_parser.sql" file under the same directory.

SET search_path = public;
BEGIN;

--DROP TEXT SEARCH CONFIGURATION testcfg;
--DROP TEXT SEARCH PARSER testparser;

CREATE OR REPLACE FUNCTION testprs_start(internal,int4)
RETURNS internal
AS '$libdir/test_parser'
LANGUAGE 'C';

CREATE OR REPLACE FUNCTION testprs_getlexeme(internal,internal,internal)
RETURNS internal
AS '$libdir/test_parser'
LANGUAGE 'C';

CREATE OR REPLACE FUNCTION testprs_end(internal)
RETURNS void
AS '$libdir/test_parser'
LANGUAGE 'C';

CREATE OR REPLACE FUNCTION testprs_lextype(internal)
RETURNS internal
AS '$libdir/test_parser'
LANGUAGE 'C';

CREATE TEXT SEARCH PARSER testparser(
START = 'testprs_start',
GETTOKEN = 'testprs_getlexeme',
END = 'testprs_end',
LEXTYPES = 'testprs_lextype'
);

CREATE TEXT SEARCH CONFIGURATION testcfg (
PARSER ='testparser'
);

ALTER TEXT SEARCH CONFIGURATION testcfg ADD MAPPING FOR word WITH english_stem;

END;

Note: the bold part is total changed for the 8.3.9 version. "DROP TEXT SEARCH " is very useful if you make modification and load the script again.

Install the parser:

• open a terminal, switch to the directory you just create. For example: cd /home/user/Desktop/test_parser
• type: sudo PATH=/usr/local/pgsql/bin:$PATH USE_PGXS=1 make install
• switch to user "prostgres", type: /usr/local/pgsql/bin/psql -f /usr/local/pgsql/share/contrib/test_parser.sql your-database

  SET
  BEGIN
  CREATE FUNCTION
  CREATE FUNCTION
  CREATE FUNCTION
  CREATE FUNCTION
  DROP TEXT SEARCH CONFIGURATION
  DROP TEXT SEARCH PARSER
  CREATE TEXT SEARCH PARSER
  CREATE TEXT SEARCH CONFIGURATION
  ALTER TEXT SEARCH CONFIGURATION
  COMMIT

• type: /usr/local/pgsql/bin/psql postgres
• test the parser:

  postgres=# SELECT to_tsvector('testcfg','itemValue');
  to_tsvector
  --------------------
  'item':1 'value':2
  (1 row)
  
  postgres=# SELECT to_tsvector('testcfg','ItemValue');
  to_tsvector
  --------------------
  'item':1 'value':2
  (1 row)
  
  postgres=# SELECT to_tsquery('testcfg','itemsValue');
  to_tsquery
  -------------------
  'items' & 'value'
  (1 row)

Reference:
[1] http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/docs/HOWTO-parser-tsearch2.html
[2] http://www.pgcon.org/2007/schedule/attachments/12-fts.pdf
[3] http://en.wikipedia.org/wiki/CamelCase
[4] http://www.sai.msu.su/~megera/postgres/fts/doc/sql-fts-createmap.html
[5] http://www.postgresql.org/docs/8.3/static/textsearch-configuration.html
[6] http://developer.postgresql.org/pgdocs/postgres/sql-createtsconfig.html
[7] http://www.postgresql.org/docs/7.4/interactive/sql-createfunction.html