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WIP: Stuff needed for FTS5

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Max Maischein 2020-08-28 13:57:10 +02:00
parent 30e4ee67e9
commit 8c076159d2
3 changed files with 799 additions and 0 deletions
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1
SQLiteXS.h
View file

@ -20,5 +20,6 @@
#include "sqlite3.h" #include "sqlite3.h"
#include "fts3_tokenizer.h" #include "fts3_tokenizer.h"
#include "fts5.h"
#endif #endif

223
dbdimp_tokenizer.inc
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@ -16,6 +16,24 @@ typedef struct perl_fts3_tokenizer_cursor {
int currentChar; /* char position corresponding to currentByte */ int currentChar; /* char position corresponding to currentByte */
} perl_fts3_tokenizer_cursor; } perl_fts3_tokenizer_cursor;
typedef struct perl_fts5_tokenizer {
fts5_tokenizer base;
SV *coderef; /* the perl tokenizer is a coderef that takes
a string and returns a cursor coderef */
} perl_fts5_tokenizer;
typedef struct perl_fts5_tokenizer_cursor {
// fts5_tokenizer_cursor base;
SV *coderef; /* ref to the closure that returns terms */
char *pToken; /* storage for a copy of the last token */
int nTokenAllocated; /* space allocated to pToken buffer */
/* members below are only used if the input string is in utf8 */
const char *pInput; /* input we are tokenizing */
const char *lastByteOffset; /* offset into pInput */
int lastCharOffset; /* char offset corresponding to lastByteOffset */
} perl_fts5_tokenizer_cursor;
/* /*
** Create a new tokenizer instance. ** Create a new tokenizer instance.
** Will be called whenever a FTS3 table is created with ** Will be called whenever a FTS3 table is created with
@ -314,3 +332,208 @@ int sqlite_db_register_fts3_perl_tokenizer(pTHX_ SV *dbh)
return sqlite3_finalize(pStmt); return sqlite3_finalize(pStmt);
} }
/*
** Create a new tokenizer instance.
** Will be called whenever a FTS5 table is created with
** CREATE .. USING fts5( ... , tokenize=perl qualified::function::name)
** where qualified::function::name is a fully qualified perl function
*/
static int perl_fts5_tokenizer_Create(
int argc, const char * const *argv,
sqlite3_tokenizer **ppTokenizer
){
dTHX;
dSP;
int n_retval;
SV *retval;
perl_fts3_tokenizer *t;
if (!argc) {
return SQLITE_ERROR;
}
t = (perl_fts3_tokenizer *) sqlite3_malloc(sizeof(*t));
if( t==NULL ) return SQLITE_NOMEM;
memset(t, 0, sizeof(*t));
ENTER;
SAVETMPS;
/* call the qualified::function::name */
PUSHMARK(SP);
PUTBACK;
n_retval = call_pv(argv[0], G_SCALAR);
SPAGAIN;
/* store a copy of the returned coderef into the tokenizer structure */
if (n_retval != 1) {
warn("tokenizer_Create returned %d arguments", n_retval);
}
retval = POPs;
t->coderef = newSVsv(retval);
*ppTokenizer = &t->base;
PUTBACK;
FREETMPS;
LEAVE;
return SQLITE_OK;
}
/*
** Destroy a tokenizer
*/
static int perl_fts5_tokenizer_Delete(Fts5Tokenizer *pTokenizer){
dTHX;
perl_fts5_tokenizer *t = (perl_fts5_tokenizer *) pTokenizer;
sv_free(t->coderef);
sqlite3_free(t);
return SQLITE_OK;
}
/*
** Extract the next token from a tokenization cursor. The cursor must
** have been opened by a prior call to perl_fts3_tokenizer_Open().
*/
static int perl_fts5_tokenizer_Tokenize(
sqlite3_tokenizer_cursor *pCursor, /* Cursor returned by perl_fts3_tokenizer_Open */
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 */
){
perl_fts3_tokenizer_cursor *c = (perl_fts3_tokenizer_cursor *) pCursor;
int result;
int n_retval;
char *token;
char *byteOffset;
STRLEN n_a; /* this is required for older perls < 5.8.8 */
I32 hop;
dTHX;
dSP;
ENTER;
SAVETMPS;
/* call the cursor */
PUSHMARK(SP);
PUTBACK;
n_retval = call_sv(c->coderef, G_ARRAY);
SPAGAIN;
/* if we get back an empty list, there is no more token */
if (n_retval == 0) {
result = SQLITE_DONE;
}
/* otherwise, get token details from the return list */
else {
if (n_retval != 5) {
warn("tokenizer cursor returned %d arguments", n_retval);
}
*piPosition = POPi;
*piEndOffset = POPi;
*piStartOffset = POPi;
*pnBytes = POPi;
token = POPpx;
if (c->pInput) { /* if working with utf8 data */
/* recompute *pnBytes in bytes, not in chars */
*pnBytes = strlen(token);
/* recompute start/end offsets in bytes, not in chars */
hop = *piStartOffset - c->lastCharOffset;
byteOffset = (char*)utf8_hop((U8*)c->lastByteOffset, hop);
hop = *piEndOffset - *piStartOffset;
*piStartOffset = byteOffset - c->pInput;
byteOffset = (char*)utf8_hop((U8*)byteOffset, hop);
*piEndOffset = byteOffset - c->pInput;
/* remember where we are for next round */
c->lastCharOffset = *piEndOffset,
c->lastByteOffset = byteOffset;
}
/* make sure we have enough storage for copying the token */
if (*pnBytes > c->nTokenAllocated ){
char *pNew;
c->nTokenAllocated = *pnBytes + 20;
pNew = sqlite3_realloc(c->pToken, c->nTokenAllocated);
if( !pNew ) return SQLITE_NOMEM;
c->pToken = pNew;
}
/* need to copy the token into the C cursor before perl frees that
memory */
memcpy(c->pToken, token, *pnBytes);
*ppToken = c->pToken;
result = SQLITE_OK;
}
PUTBACK;
FREETMPS;
LEAVE;
return result;
}
/*
** The set of routines that implement the perl FTS5 tokenizer
*/
fts5_tokenizer perl_fts5_tokenizer_Module = {
0,
perl_fts5_tokenizer_Create,
perl_fts5_tokenizer_Delete,
perl_fts5_tokenizer_Tokenize
};
/*
** Fetch the FTS5 API pointers
*/
fts5_api* sqlite_fetch_fts5_api(pTHX_ SV *dbh)
{
D_imp_dbh(dbh);
int rc;
sqlite3_stmt *pStmt;
const char zSql[] = "SELECT fts5(?)";
fts5_api *pFts5Api = 0;
if (!DBIc_ACTIVE(imp_dbh)) {
sqlite_error(dbh, -2, "attempt to register fts5 tokenizer on inactive database handle");
return FALSE;
}
rc = sqlite3_prepare_v2(imp_dbh->db, zSql, -1, &pStmt, 0);
if( rc!=SQLITE_OK ){
return 0;
}
sqlite3_bind_pointer(pStmt, 1, (void*)&pFts5Api, "fts5_api_ptr", NULL);
sqlite3_step(pStmt);
sqlite3_finalize(pStmt);
return pFts5Api;
}
/*
** Register the perl tokenizer with FTS5
*/
int sqlite_db_register_fts5_perl_tokenizer(pTHX_ SV *dbh)
{
D_imp_dbh(dbh);
int rc;
fts5_api *pFts5Api = sqlite_fetch_fts5_api(aTHX_ dbh);
sqlite3_tokenizer_module *p = &perl_fts5_tokenizer_Module;
// pFts5Api->xCreateTokenizer(pFts5Api,...);
return 0;
}

575
fts5.h Normal file
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@ -0,0 +1,575 @@
/*
** 2014 May 31
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
******************************************************************************
**
** Interfaces to extend FTS5. Using the interfaces defined in this file,
** FTS5 may be extended with:
**
** * custom tokenizers, and
** * custom auxiliary functions.
*/
#ifndef _FTS5_H
#define _FTS5_H
#include "sqlite3.h"
#ifdef __cplusplus
extern "C" {
#endif
/*************************************************************************
** CUSTOM AUXILIARY FUNCTIONS
**
** Virtual table implementations may overload SQL functions by implementing
** the sqlite3_module.xFindFunction() method.
*/
typedef struct Fts5ExtensionApi Fts5ExtensionApi;
typedef struct Fts5Context Fts5Context;
typedef struct Fts5PhraseIter Fts5PhraseIter;
typedef void (*fts5_extension_function)(
const Fts5ExtensionApi *pApi, /* API offered by current FTS version */
Fts5Context *pFts, /* First arg to pass to pApi functions */
sqlite3_context *pCtx, /* Context for returning result/error */
int nVal, /* Number of values in apVal[] array */
sqlite3_value **apVal /* Array of trailing arguments */
);
struct Fts5PhraseIter {
const unsigned char *a;
const unsigned char *b;
};
/*
** EXTENSION API FUNCTIONS
**
** xUserData(pFts):
** Return a copy of the context pointer the extension function was
** registered with.
**
** xColumnTotalSize(pFts, iCol, pnToken):
** If parameter iCol is less than zero, set output variable *pnToken
** to the total number of tokens in the FTS5 table. Or, if iCol is
** non-negative but less than the number of columns in the table, return
** the total number of tokens in column iCol, considering all rows in
** the FTS5 table.
**
** If parameter iCol is greater than or equal to the number of columns
** in the table, SQLITE_RANGE is returned. Or, if an error occurs (e.g.
** an OOM condition or IO error), an appropriate SQLite error code is
** returned.
**
** xColumnCount(pFts):
** Return the number of columns in the table.
**
** xColumnSize(pFts, iCol, pnToken):
** If parameter iCol is less than zero, set output variable *pnToken
** to the total number of tokens in the current row. Or, if iCol is
** non-negative but less than the number of columns in the table, set
** *pnToken to the number of tokens in column iCol of the current row.
**
** If parameter iCol is greater than or equal to the number of columns
** in the table, SQLITE_RANGE is returned. Or, if an error occurs (e.g.
** an OOM condition or IO error), an appropriate SQLite error code is
** returned.
**
** This function may be quite inefficient if used with an FTS5 table
** created with the "columnsize=0" option.
**
** xColumnText:
** This function attempts to retrieve the text of column iCol of the
** current document. If successful, (*pz) is set to point to a buffer
** containing the text in utf-8 encoding, (*pn) is set to the size in bytes
** (not characters) of the buffer and SQLITE_OK is returned. Otherwise,
** if an error occurs, an SQLite error code is returned and the final values
** of (*pz) and (*pn) are undefined.
**
** xPhraseCount:
** Returns the number of phrases in the current query expression.
**
** xPhraseSize:
** Returns the number of tokens in phrase iPhrase of the query. Phrases
** are numbered starting from zero.
**
** xInstCount:
** Set *pnInst to the total number of occurrences of all phrases within
** the query within the current row. Return SQLITE_OK if successful, or
** an error code (i.e. SQLITE_NOMEM) if an error occurs.
**
** This API can be quite slow if used with an FTS5 table created with the
** "detail=none" or "detail=column" option. If the FTS5 table is created
** with either "detail=none" or "detail=column" and "content=" option
** (i.e. if it is a contentless table), then this API always returns 0.
**
** xInst:
** Query for the details of phrase match iIdx within the current row.
** Phrase matches are numbered starting from zero, so the iIdx argument
** should be greater than or equal to zero and smaller than the value
** output by xInstCount().
**
** Usually, output parameter *piPhrase is set to the phrase number, *piCol
** to the column in which it occurs and *piOff the token offset of the
** first token of the phrase. Returns SQLITE_OK if successful, or an error
** code (i.e. SQLITE_NOMEM) if an error occurs.
**
** This API can be quite slow if used with an FTS5 table created with the
** "detail=none" or "detail=column" option.
**
** xRowid:
** Returns the rowid of the current row.
**
** xTokenize:
** Tokenize text using the tokenizer belonging to the FTS5 table.
**
** xQueryPhrase(pFts5, iPhrase, pUserData, xCallback):
** This API function is used to query the FTS table for phrase iPhrase
** of the current query. Specifically, a query equivalent to:
**
** ... FROM ftstable WHERE ftstable MATCH $p ORDER BY rowid
**
** with $p set to a phrase equivalent to the phrase iPhrase of the
** current query is executed. Any column filter that applies to
** phrase iPhrase of the current query is included in $p. For each
** row visited, the callback function passed as the fourth argument
** is invoked. The context and API objects passed to the callback
** function may be used to access the properties of each matched row.
** Invoking Api.xUserData() returns a copy of the pointer passed as
** the third argument to pUserData.
**
** If the callback function returns any value other than SQLITE_OK, the
** query is abandoned and the xQueryPhrase function returns immediately.
** If the returned value is SQLITE_DONE, xQueryPhrase returns SQLITE_OK.
** Otherwise, the error code is propagated upwards.
**
** If the query runs to completion without incident, SQLITE_OK is returned.
** Or, if some error occurs before the query completes or is aborted by
** the callback, an SQLite error code is returned.
**
**
** xSetAuxdata(pFts5, pAux, xDelete)
**
** Save the pointer passed as the second argument as the extension function's
** "auxiliary data". The pointer may then be retrieved by the current or any
** future invocation of the same fts5 extension function made as part of
** the same MATCH query using the xGetAuxdata() API.
**
** Each extension function is allocated a single auxiliary data slot for
** each FTS query (MATCH expression). If the extension function is invoked
** more than once for a single FTS query, then all invocations share a
** single auxiliary data context.
**
** If there is already an auxiliary data pointer when this function is
** invoked, then it is replaced by the new pointer. If an xDelete callback
** was specified along with the original pointer, it is invoked at this
** point.
**
** The xDelete callback, if one is specified, is also invoked on the
** auxiliary data pointer after the FTS5 query has finished.
**
** If an error (e.g. an OOM condition) occurs within this function,
** the auxiliary data is set to NULL and an error code returned. If the
** xDelete parameter was not NULL, it is invoked on the auxiliary data
** pointer before returning.
**
**
** xGetAuxdata(pFts5, bClear)
**
** Returns the current auxiliary data pointer for the fts5 extension
** function. See the xSetAuxdata() method for details.
**
** If the bClear argument is non-zero, then the auxiliary data is cleared
** (set to NULL) before this function returns. In this case the xDelete,
** if any, is not invoked.
**
**
** xRowCount(pFts5, pnRow)
**
** This function is used to retrieve the total number of rows in the table.
** In other words, the same value that would be returned by:
**
** SELECT count(*) FROM ftstable;
**
** xPhraseFirst()
** This function is used, along with type Fts5PhraseIter and the xPhraseNext
** method, to iterate through all instances of a single query phrase within
** the current row. This is the same information as is accessible via the
** xInstCount/xInst APIs. While the xInstCount/xInst APIs are more convenient
** to use, this API may be faster under some circumstances. To iterate
** through instances of phrase iPhrase, use the following code:
**
** Fts5PhraseIter iter;
** int iCol, iOff;
** for(pApi->xPhraseFirst(pFts, iPhrase, &iter, &iCol, &iOff);
** iCol>=0;
** pApi->xPhraseNext(pFts, &iter, &iCol, &iOff)
** ){
** // An instance of phrase iPhrase at offset iOff of column iCol
** }
**
** The Fts5PhraseIter structure is defined above. Applications should not
** modify this structure directly - it should only be used as shown above
** with the xPhraseFirst() and xPhraseNext() API methods (and by
** xPhraseFirstColumn() and xPhraseNextColumn() as illustrated below).
**
** This API can be quite slow if used with an FTS5 table created with the
** "detail=none" or "detail=column" option. If the FTS5 table is created
** with either "detail=none" or "detail=column" and "content=" option
** (i.e. if it is a contentless table), then this API always iterates
** through an empty set (all calls to xPhraseFirst() set iCol to -1).
**
** xPhraseNext()
** See xPhraseFirst above.
**
** xPhraseFirstColumn()
** This function and xPhraseNextColumn() are similar to the xPhraseFirst()
** and xPhraseNext() APIs described above. The difference is that instead
** of iterating through all instances of a phrase in the current row, these
** APIs are used to iterate through the set of columns in the current row
** that contain one or more instances of a specified phrase. For example:
**
** Fts5PhraseIter iter;
** int iCol;
** for(pApi->xPhraseFirstColumn(pFts, iPhrase, &iter, &iCol);
** iCol>=0;
** pApi->xPhraseNextColumn(pFts, &iter, &iCol)
** ){
** // Column iCol contains at least one instance of phrase iPhrase
** }
**
** This API can be quite slow if used with an FTS5 table created with the
** "detail=none" option. If the FTS5 table is created with either
** "detail=none" "content=" option (i.e. if it is a contentless table),
** then this API always iterates through an empty set (all calls to
** xPhraseFirstColumn() set iCol to -1).
**
** The information accessed using this API and its companion
** xPhraseFirstColumn() may also be obtained using xPhraseFirst/xPhraseNext
** (or xInst/xInstCount). The chief advantage of this API is that it is
** significantly more efficient than those alternatives when used with
** "detail=column" tables.
**
** xPhraseNextColumn()
** See xPhraseFirstColumn above.
*/
struct Fts5ExtensionApi {
int iVersion; /* Currently always set to 3 */
void *(*xUserData)(Fts5Context*);
int (*xColumnCount)(Fts5Context*);
int (*xRowCount)(Fts5Context*, sqlite3_int64 *pnRow);
int (*xColumnTotalSize)(Fts5Context*, int iCol, sqlite3_int64 *pnToken);
int (*xTokenize)(Fts5Context*,
const char *pText, int nText, /* Text to tokenize */
void *pCtx, /* Context passed to xToken() */
int (*xToken)(void*, int, const char*, int, int, int) /* Callback */
);
int (*xPhraseCount)(Fts5Context*);
int (*xPhraseSize)(Fts5Context*, int iPhrase);
int (*xInstCount)(Fts5Context*, int *pnInst);
int (*xInst)(Fts5Context*, int iIdx, int *piPhrase, int *piCol, int *piOff);
sqlite3_int64 (*xRowid)(Fts5Context*);
int (*xColumnText)(Fts5Context*, int iCol, const char **pz, int *pn);
int (*xColumnSize)(Fts5Context*, int iCol, int *pnToken);
int (*xQueryPhrase)(Fts5Context*, int iPhrase, void *pUserData,
int(*)(const Fts5ExtensionApi*,Fts5Context*,void*)
);
int (*xSetAuxdata)(Fts5Context*, void *pAux, void(*xDelete)(void*));
void *(*xGetAuxdata)(Fts5Context*, int bClear);
int (*xPhraseFirst)(Fts5Context*, int iPhrase, Fts5PhraseIter*, int*, int*);
void (*xPhraseNext)(Fts5Context*, Fts5PhraseIter*, int *piCol, int *piOff);
int (*xPhraseFirstColumn)(Fts5Context*, int iPhrase, Fts5PhraseIter*, int*);
void (*xPhraseNextColumn)(Fts5Context*, Fts5PhraseIter*, int *piCol);
};
/*
** CUSTOM AUXILIARY FUNCTIONS
*************************************************************************/
/*************************************************************************
** CUSTOM TOKENIZERS
**
** Applications may also register custom tokenizer types. A tokenizer
** is registered by providing fts5 with a populated instance of the
** following structure. All structure methods must be defined, setting
** any member of the fts5_tokenizer struct to NULL leads to undefined
** behaviour. The structure methods are expected to function as follows:
**
** xCreate:
** This function is used to allocate and initialize a tokenizer instance.
** A tokenizer instance is required to actually tokenize text.
**
** The first argument passed to this function is a copy of the (void*)
** pointer provided by the application when the fts5_tokenizer object
** was registered with FTS5 (the third argument to xCreateTokenizer()).
** The second and third arguments are an array of nul-terminated strings
** containing the tokenizer arguments, if any, specified following the
** tokenizer name as part of the CREATE VIRTUAL TABLE statement used
** to create the FTS5 table.
**
** The final argument is an output variable. If successful, (*ppOut)
** should be set to point to the new tokenizer handle and SQLITE_OK
** returned. If an error occurs, some value other than SQLITE_OK should
** be returned. In this case, fts5 assumes that the final value of *ppOut
** is undefined.
**
** xDelete:
** This function is invoked to delete a tokenizer handle previously
** allocated using xCreate(). Fts5 guarantees that this function will
** be invoked exactly once for each successful call to xCreate().
**
** xTokenize:
** This function is expected to tokenize the nText byte string indicated
** by argument pText. pText may or may not be nul-terminated. The first
** argument passed to this function is a pointer to an Fts5Tokenizer object
** returned by an earlier call to xCreate().
**
** The second argument indicates the reason that FTS5 is requesting
** tokenization of the supplied text. This is always one of the following
** four values:
**
** <ul><li> <b>FTS5_TOKENIZE_DOCUMENT</b> - A document is being inserted into
** or removed from the FTS table. The tokenizer is being invoked to
** determine the set of tokens to add to (or delete from) the
** FTS index.
**
** <li> <b>FTS5_TOKENIZE_QUERY</b> - A MATCH query is being executed
** against the FTS index. The tokenizer is being called to tokenize
** a bareword or quoted string specified as part of the query.
**
** <li> <b>(FTS5_TOKENIZE_QUERY | FTS5_TOKENIZE_PREFIX)</b> - Same as
** FTS5_TOKENIZE_QUERY, except that the bareword or quoted string is
** followed by a "*" character, indicating that the last token
** returned by the tokenizer will be treated as a token prefix.
**
** <li> <b>FTS5_TOKENIZE_AUX</b> - The tokenizer is being invoked to
** satisfy an fts5_api.xTokenize() request made by an auxiliary
** function. Or an fts5_api.xColumnSize() request made by the same
** on a columnsize=0 database.
** </ul>
**
** For each token in the input string, the supplied callback xToken() must
** be invoked. The first argument to it should be a copy of the pointer
** passed as the second argument to xTokenize(). The third and fourth
** arguments are a pointer to a buffer containing the token text, and the
** size of the token in bytes. The 4th and 5th arguments are the byte offsets
** of the first byte of and first byte immediately following the text from
** which the token is derived within the input.
**
** The second argument passed to the xToken() callback ("tflags") should
** normally be set to 0. The exception is if the tokenizer supports
** synonyms. In this case see the discussion below for details.
**
** FTS5 assumes the xToken() callback is invoked for each token in the
** order that they occur within the input text.
**
** If an xToken() callback returns any value other than SQLITE_OK, then
** the tokenization should be abandoned and the xTokenize() method should
** immediately return a copy of the xToken() return value. Or, if the
** input buffer is exhausted, xTokenize() should return SQLITE_OK. Finally,
** if an error occurs with the xTokenize() implementation itself, it
** may abandon the tokenization and return any error code other than
** SQLITE_OK or SQLITE_DONE.
**
** SYNONYM SUPPORT
**
** Custom tokenizers may also support synonyms. Consider a case in which a
** user wishes to query for a phrase such as "first place". Using the
** built-in tokenizers, the FTS5 query 'first + place' will match instances
** of "first place" within the document set, but not alternative forms
** such as "1st place". In some applications, it would be better to match
** all instances of "first place" or "1st place" regardless of which form
** the user specified in the MATCH query text.
**
** There are several ways to approach this in FTS5:
**
** <ol><li> By mapping all synonyms to a single token. In this case, using
** the above example, this means that the tokenizer returns the
** same token for inputs "first" and "1st". Say that token is in
** fact "first", so that when the user inserts the document "I won
** 1st place" entries are added to the index for tokens "i", "won",
** "first" and "place". If the user then queries for '1st + place',
** the tokenizer substitutes "first" for "1st" and the query works
** as expected.
**
** <li> By querying the index for all synonyms of each query term
** separately. In this case, when tokenizing query text, the
** tokenizer may provide multiple synonyms for a single term
** within the document. FTS5 then queries the index for each
** synonym individually. For example, faced with the query:
**
** <codeblock>
** ... MATCH 'first place'</codeblock>
**
** the tokenizer offers both "1st" and "first" as synonyms for the
** first token in the MATCH query and FTS5 effectively runs a query
** similar to:
**
** <codeblock>
** ... MATCH '(first OR 1st) place'</codeblock>
**
** except that, for the purposes of auxiliary functions, the query
** still appears to contain just two phrases - "(first OR 1st)"
** being treated as a single phrase.
**
** <li> By adding multiple synonyms for a single term to the FTS index.
** Using this method, when tokenizing document text, the tokenizer
** provides multiple synonyms for each token. So that when a
** document such as "I won first place" is tokenized, entries are
** added to the FTS index for "i", "won", "first", "1st" and
** "place".
**
** This way, even if the tokenizer does not provide synonyms
** when tokenizing query text (it should not - to do so would be
** inefficient), it doesn't matter if the user queries for
** 'first + place' or '1st + place', as there are entries in the
** FTS index corresponding to both forms of the first token.
** </ol>
**
** Whether it is parsing document or query text, any call to xToken that
** specifies a <i>tflags</i> argument with the FTS5_TOKEN_COLOCATED bit
** is considered to supply a synonym for the previous token. For example,
** when parsing the document "I won first place", a tokenizer that supports
** synonyms would call xToken() 5 times, as follows:
**
** <codeblock>
** xToken(pCtx, 0, "i", 1, 0, 1);
** xToken(pCtx, 0, "won", 3, 2, 5);
** xToken(pCtx, 0, "first", 5, 6, 11);
** xToken(pCtx, FTS5_TOKEN_COLOCATED, "1st", 3, 6, 11);
** xToken(pCtx, 0, "place", 5, 12, 17);
**</codeblock>
**
** It is an error to specify the FTS5_TOKEN_COLOCATED flag the first time
** xToken() is called. Multiple synonyms may be specified for a single token
** by making multiple calls to xToken(FTS5_TOKEN_COLOCATED) in sequence.
** There is no limit to the number of synonyms that may be provided for a
** single token.
**
** In many cases, method (1) above is the best approach. It does not add
** extra data to the FTS index or require FTS5 to query for multiple terms,
** so it is efficient in terms of disk space and query speed. However, it
** does not support prefix queries very well. If, as suggested above, the
** token "first" is substituted for "1st" by the tokenizer, then the query:
**
** <codeblock>
** ... MATCH '1s*'</codeblock>
**
** will not match documents that contain the token "1st" (as the tokenizer
** will probably not map "1s" to any prefix of "first").
**
** For full prefix support, method (3) may be preferred. In this case,
** because the index contains entries for both "first" and "1st", prefix
** queries such as 'fi*' or '1s*' will match correctly. However, because
** extra entries are added to the FTS index, this method uses more space
** within the database.
**
** Method (2) offers a midpoint between (1) and (3). Using this method,
** a query such as '1s*' will match documents that contain the literal
** token "1st", but not "first" (assuming the tokenizer is not able to
** provide synonyms for prefixes). However, a non-prefix query like '1st'
** will match against "1st" and "first". This method does not require
** extra disk space, as no extra entries are added to the FTS index.
** On the other hand, it may require more CPU cycles to run MATCH queries,
** as separate queries of the FTS index are required for each synonym.
**
** When using methods (2) or (3), it is important that the tokenizer only
** provide synonyms when tokenizing document text (method (2)) or query
** text (method (3)), not both. Doing so will not cause any errors, but is
** inefficient.
*/
typedef struct Fts5Tokenizer Fts5Tokenizer;
typedef struct fts5_tokenizer fts5_tokenizer;
struct fts5_tokenizer {
int (*xCreate)(void*, const char **azArg, int nArg, Fts5Tokenizer **ppOut);
void (*xDelete)(Fts5Tokenizer*);
int (*xTokenize)(Fts5Tokenizer*,
void *pCtx,
int flags, /* Mask of FTS5_TOKENIZE_* flags */
const char *pText, int nText,
int (*xToken)(
void *pCtx, /* Copy of 2nd argument to xTokenize() */
int tflags, /* Mask of FTS5_TOKEN_* flags */
const char *pToken, /* Pointer to buffer containing token */
int nToken, /* Size of token in bytes */
int iStart, /* Byte offset of token within input text */
int iEnd /* Byte offset of end of token within input text */
)
);
};
/* Flags that may be passed as the third argument to xTokenize() */
#define FTS5_TOKENIZE_QUERY 0x0001
#define FTS5_TOKENIZE_PREFIX 0x0002
#define FTS5_TOKENIZE_DOCUMENT 0x0004
#define FTS5_TOKENIZE_AUX 0x0008
/* Flags that may be passed by the tokenizer implementation back to FTS5
** as the third argument to the supplied xToken callback. */
#define FTS5_TOKEN_COLOCATED 0x0001 /* Same position as prev. token */
/*
** END OF CUSTOM TOKENIZERS
*************************************************************************/
/*************************************************************************
** FTS5 EXTENSION REGISTRATION API
*/
typedef struct fts5_api fts5_api;
struct fts5_api {
int iVersion; /* Currently always set to 2 */
/* Create a new tokenizer */
int (*xCreateTokenizer)(
fts5_api *pApi,
const char *zName,
void *pContext,
fts5_tokenizer *pTokenizer,
void (*xDestroy)(void*)
);
/* Find an existing tokenizer */
int (*xFindTokenizer)(
fts5_api *pApi,
const char *zName,
void **ppContext,
fts5_tokenizer *pTokenizer
);
/* Create a new auxiliary function */
int (*xCreateFunction)(
fts5_api *pApi,
const char *zName,
void *pContext,
fts5_extension_function xFunction,
void (*xDestroy)(void*)
);
};
/*
** END OF REGISTRATION API
*************************************************************************/
#ifdef __cplusplus
} /* end of the 'extern "C"' block */
#endif
#endif /* _FTS5_H */