摘自：
http://hi.baidu.com/xjtukanif/blog/item/8e7a4ea5362abf99d14358e2.html sqlite3通过使用
fts3虚表支持全文搜索，默认支持simple和porter两种分词器，并提供了接口来自定义分词器。这里我们利用
mmseg来构造自定义的中文分词器。
虽然sqlite在fts3_tokenizer.h中提供了各种接口供用户自定义分词器，但其并未提供c函数供用户来注册自定义的分词器，分词器的注册必须使用sql语句来完成。
SELECT fts3_tokenizer(<tokenizer-name>, <sqlite3_tokenizer_module ptr>);
其中tokenizer-name是分词器的名称，sqlite3_tokenizer_module ptr只一个指向sqlite3_tokenizer_module结构的指针并且编码为SQL blob。下面是官方给出的注册函数：
int registerTokenizer(
sqlite3 *db,
char *zName,
const sqlite3_tokenizer_module *p
){
int rc;
sqlite3_stmt *pStmt;
const char *zSql = "SELECT fts3_tokenizer(?, ?)";
rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
if( rc!=SQLITE_OK ){
return rc;
}
sqlite3_bind_text(pStmt, 1, zName, -1, SQLITE_STATIC);
sqlite3_bind_blob(pStmt, 2, &p, sizeof(p), SQLITE_STATIC);
sqlite3_step(pStmt);
return sqlite3_finalize(pStmt);
}
要想实现自定义的分词器，最关键的时是得到指向sqlite3_tokenizer_module结构的一个指针，sqlite3_tokenizer_module结构体定义如下：
struct sqlite3_tokenizer_module {
int iVersion; //版本号，必须设置为0
int (*xCreate)( //创建虚表时自动调用并创建分词器
int argc,
const char *const*argv,
sqlite3_tokenizer **ppTokenizer
);
int (*xDestroy)(sqlite3_tokenizer *pTokenizer); //数据库连接关闭时自动调用，用于销毁资源
int (*xOpen)( //插入数据或检索时自动调用以进行分词
sqlite3_tok enizer *pTokenizer,
const char *pInput, int nBytes,
sqlite3_tokenizer_cursor **ppCursor
);
int (*xClose)(sqlite3_tokenizer_cursor *pCursor); //分词结果提取完毕后自动调用
int (*xNext)( //逐个提取分词结果
sqlite3_tokenizer_cursor *pCursor,
const char **ppToken, int *pnBytes,
int *piStartOffset,
int *piEndOffset,
int *piPosition
);
};
有几点需要注意的是：
1 分词引擎使用sql语句注册意味着每建立一个sqlite连接都必须注册一次分词器，对于需要使用词库的中文分词器来说也意味着巨大的内存消耗。
2 在检索时分词结果的提取和语义的解析式交替进行的。例如我们搜索"kanif OR sqlite"的时候，引擎先将全部传入到分词器，在调用一次next获取到词 kanif后，在将词sqlite传入到分词器，直到全部解析完毕。
3 由于中文分词本身的特殊性，例如"北京市"很有可能视为一个完整的词，这样在搜索"北京"的时候就无法获取到结果。如果分词器支持将"北京市"切分为"北 京市"和"北京"或者将十一月切分为"11月"和"十一"，那么需注意(*xNext)函数中的piStartOffset和piEndOffset参 数。经测试在插入数据的时候这两个参数无实际用途，但在查询的时候这两个参数决定了下一次的输入串。
附：
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include "fts3_tokenizer.h"
#include "mmseg/mmseg.cpp"
static bool loadDic = true;
typedef struct cus_tokenizer {
sqlite3_tokenizer base;
} cus_tokenizer;
typedef struct cus_tokenizer_cursor {
sqlite3_tokenizer_cursor base;
char *pInput;
int nBytes;
int iToken;
char *pToken;
rmmseg::Algorithm *pAlgor;
} cus_tokenizer_cursor;
void initmmseg(void){
if(!loadDic)
return;
mmseg_load_words("chars.dic");
mmseg_load_words("words.dic");
loadDic = False;
}
static int cusCreate(
int argc, const char * const *argv,
sqlite3_tokenizer **ppTokenizer
){
cus_tokenizer *t;
t = (cus_tokenizer *) sqlite3_malloc(sizeof(*t));
if( t==NULL ) return SQLITE_NOMEM;
memset(t, 0, sizeof(*t));
initmmseg();
*ppTokenizer = &t->base;
return SQLITE_OK;
}
static int cusDestroy(sqlite3_tokenizer *pTokenizer){
sqlite3_free(pTokenizer);
return SQLITE_OK;
}
static int cusOpen(
sqlite3_tokenizer *pTokenizer, /* The tokenizer */
const char *pInput, int nBytes, /* String to be tokenized */
sqlite3_tokenizer_cursor **ppCursor /* OUT: Tokenization cursor */
){
cus_tokenizer_cursor *c;
if(pInput == 0){
nBytes = 0;
}else if(nBytes < 0)
nBytes = (int)strlen(pInput);
c = (cus_tokenizer_cursor *) sqlite3_malloc(sizeof(*c));
if(c == NULL)
return SQLITE_NOMEM;
c->iToken = c->nBytes = 0;
c->pInput = c->pToken = NULL;
c->pAlgor = mmseg_algor_create(pInput, nBytes);
c->nBytes = nBytes;
*ppCursor = &c->base;
return SQLITE_OK;
}
static int cusClose(sqlite3_tokenizer_cursor *pCursor){
cus_tokenizer_cursor *c = (cus_tokenizer_cursor *) pCursor;
if(c->pInput != NULL){
sqlite3_free(c->pInput);
}
if(c->pToken != NULL){
sqlite3_free(c->pToken);
}
if(c->pAlgor != NULL){
mmseg_algor_destroy(c->pAlgor);
}
c->pInput = c->pToken = NULL;
c->pAlgor = NULL;
sqlite3_free(c);
return SQLITE_OK;
}
/*
1 sqlite只有在插入数据的时候才使用cursor遍历
2 在进行数据查询时，只会进入一次，然后使用piStartOffset与piEndOffset根据原始串重新生成查询串
*/
static int cusNext(
sqlite3_tokenizer_cursor *pCursor, /* Cursor returned by cusOpen */
const char **ppToken, /* OUT: *ppToken is the token text */
int *pnBytes, /* OUT: Number of bytes in token */
int *piStartOffset, /* OUT: Starting offset of token */
int *piEndOffset, /* OUT: Ending offset of token */
int *piPosition /* OUT: Position integer of token */
){
cus_tokenizer_cursor *c = (cus_tokenizer_cursor *) pCursor;
cus_tokenizer *t = (cus_tokenizer *) pCursor->pTokenizer;
if(c->pToken != NULL){
sqlite3_free(c->pToken);
c->pToken = NULL;
}
struct Token token = mmseg_next_token(c->pAlgor);
if(token.length != 0 ){
int l = token.length;
c->pToken = (char *)sqlite3_malloc(l+1);
if(c->pToken == NULL)
return SQLITE_NOMEM;
c->pToken[l] = 0;
memcpy(c->pToken, token.text, l);
*ppToken = c->pToken;
*pnBytes = l;
*piStartOffset = token.offset;
*piEndOffset = token.offset + token.length;
*piPosition = c->iToken++;
return SQLITE_OK;
}
//一般来说只有插入数据时才会进入到这里
return SQLITE_DONE;
}
static const sqlite3_tokenizer_module cusTokenizerModule = {
0,
cusCreate,
cusDestroy,
cusOpen,
cusClose,
cusNext,
};
int registerTokenizer(
sqlite3 *db,
char *zName,
const sqlite3_tokenizer_module *p
){
int rc;
sqlite3_stmt *pStmt;
const char *zSql = "SELECT fts3_tokenizer(?, ?)";
rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
if( rc!=SQLITE_OK ){
return rc;
}
sqlite3_bind_text(pStmt, 1, zName, -1, SQLITE_STATIC);
sqlite3_bind_blob(pStmt, 2, &p, sizeof(p), SQLITE_STATIC);
sqlite3_step(pStmt);
return sqlite3_finalize(pStmt);
}
int main(){
const sqlite3_tokenizer_module *ptr = &cusTokenizerModule;
sqlite3 *pDB;
sqlite3_stmt * stmt;
char * errMsg = NULL;
const char *zTail;
int rc = sqlite3_open("test.sqlite3", &pDB);
if(rc){
printf("create error. %s\n",sqlite3_errmsg(pDB));
return rc;
}
char token_name[] = "custoken";
registerTokenizer(pDB, token_name, ptr);
rc = sqlite3_exec(pDB, "CREATE VIRTUAL TABLE foo USING fts3(tokenize=custoken)", 0, 0, &errMsg);
if(rc != SQLITE_OK){
printf("create virtual error, %s\n", errMsg);
if(rc != SQLITE_OK){
printf("create virtual error, %s\n", errMsg);
return rc;
}
rc = sqlite3_exec(pDB, "INSERT INTO foo VALUES('\xe5\x8c\x97\xe4\xba\xac\xe5\xb8\x82')", 0, 0, &errMsg);
if(rc != SQLITE_OK){
printf("insert value error, %s\n", errMsg);
return rc;
}
int nrow = 0, ncolumn = 0;
char **azResult; //二维数组存放结果
sqlite3_get_table(pDB , "SELECT * FROM foo WHERE content MATCH '\xe5\x8c\x97\xe4\xba\xac\xe5\xb8\x82'" , &azResult , &nrow , &ncolumn , &errMsg );
int i = 0 ;
printf( "row:%d column=%d \n" , nrow , ncolumn );
printf( "\nThe result of querying is : \n" );
for( i=0 ; i<( nrow + 1 ) * ncolumn ; i++ )
printf( "azResult[%d] = %s\n", i , azResult[i] );
sqlite3_free_table( azResult );
sqlite3_close(pDB);
return 0;
}
