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Add the experimental "stmts" virtual table for introspection of prepared

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statements.

FossilOrigin-Name: cb4c5c66aba757356da3b8ec3c66a5c8c40e180b3360638ac634f7787404a5b1
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drh
2017-05-31 16:09:04 +00:00
parent d4ab003d4e
commit 6b37e0adc9
3 changed files with 304 additions and 6 deletions
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ext/misc/stmts.c
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/*
** 2017-05-31
**
** 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.
**
*************************************************************************
**
** This file demonstrates an eponymous virtual table that returns information
** about all prepared statements for the database connection.
**
** Usage example:
**
** .load ./stmts
** .mode line
** .header on
** SELECT * FROM stmts;
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>
#ifndef SQLITE_OMIT_VIRTUALTABLE
/*
** The following macros are used to cast pointers to integers.
** The way you do this varies from one compiler
** to the next, so we have developed the following set of #if statements
** to generate appropriate macros for a wide range of compilers.
*/
#if defined(__PTRDIFF_TYPE__) /* This case should work for GCC */
# define SQLITE_PTR_TO_INT64(X) ((sqlite3_int64)(__PTRDIFF_TYPE__)(X))
#elif !defined(__GNUC__) /* Works for compilers other than LLVM */
# define SQLITE_PTR_TO_INT64(X) ((sqlite3_int64)(((char*)X)-(char*)0))
#elif defined(HAVE_STDINT_H) /* Use this case if we have ANSI headers */
# define SQLITE_PTR_TO_INT64(X) ((sqlite3_int64)(intptr_t)(X))
#else /* Generates a warning - but it always works */
# define SQLITE_PTR_TO_INT64(X) ((sqlite3_int64)(X))
#endif
/* stmts_vtab is a subclass of sqlite3_vtab which will
** serve as the underlying representation of a stmts virtual table
*/
typedef struct stmts_vtab stmts_vtab;
struct stmts_vtab {
sqlite3_vtab base; /* Base class - must be first */
sqlite3 *db; /* Database connection for this stmts vtab */
};
/* stmts_cursor is a subclass of sqlite3_vtab_cursor which will
** serve as the underlying representation of a cursor that scans
** over rows of the result
*/
typedef struct stmts_cursor stmts_cursor;
struct stmts_cursor {
sqlite3_vtab_cursor base; /* Base class - must be first */
sqlite3 *db; /* Database connection for this cursor */
sqlite3_stmt *pStmt; /* Statement cursor is currently pointing at */
sqlite3_int64 iRowid; /* The rowid */
};
/*
** The stmtsConnect() method is invoked to create a new
** stmts_vtab that describes the generate_stmts virtual table.
**
** Think of this routine as the constructor for stmts_vtab objects.
**
** All this routine needs to do is:
**
** (1) Allocate the stmts_vtab object and initialize all fields.
**
** (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the
** result set of queries against generate_stmts will look like.
*/
static int stmtsConnect(
sqlite3 *db,
void *pAux,
int argc, const char *const*argv,
sqlite3_vtab **ppVtab,
char **pzErr
){
stmts_vtab *pNew;
int rc;
/* Column numbers */
#define STMTS_COLUMN_PTR 0 /* Numeric value of the statement pointer */
#define STMTS_COLUMN_SQL 1 /* SQL for the statement */
#define STMTS_COLUMN_NCOL 2 /* Number of result columns */
#define STMTS_COLUMN_RO 3 /* True if read-only */
#define STMTS_COLUMN_BUSY 4 /* True if currently busy */
#define STMTS_COLUMN_NSCAN 5 /* SQLITE_STMTSTATUS_FULLSCAN_STEP */
#define STMTS_COLUMN_NSORT 6 /* SQLITE_STMTSTATUS_SORT */
#define STMTS_COLUMN_NAIDX 7 /* SQLITE_STMTSTATUS_AUTOINDEX */
#define STMTS_COLUMN_NSTEP 8 /* SQLITE_STMTSTATUS_VM_STEP */
rc = sqlite3_declare_vtab(db,
"CREATE TABLE x(ptr,sql,ncol,ro,busy,nscan,nsort,naidx,nstep)");
if( rc==SQLITE_OK ){
pNew = sqlite3_malloc( sizeof(*pNew) );
*ppVtab = (sqlite3_vtab*)pNew;
if( pNew==0 ) return SQLITE_NOMEM;
memset(pNew, 0, sizeof(*pNew));
pNew->db = db;
}
return rc;
}
/*
** This method is the destructor for stmts_cursor objects.
*/
static int stmtsDisconnect(sqlite3_vtab *pVtab){
sqlite3_free(pVtab);
return SQLITE_OK;
}
/*
** Constructor for a new stmts_cursor object.
*/
static int stmtsOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){
stmts_cursor *pCur;
pCur = sqlite3_malloc( sizeof(*pCur) );
if( pCur==0 ) return SQLITE_NOMEM;
memset(pCur, 0, sizeof(*pCur));
pCur->db = ((stmts_vtab*)p)->db;
*ppCursor = &pCur->base;
return SQLITE_OK;
}
/*
** Destructor for a stmts_cursor.
*/
static int stmtsClose(sqlite3_vtab_cursor *cur){
sqlite3_free(cur);
return SQLITE_OK;
}
/*
** Advance a stmts_cursor to its next row of output.
*/
static int stmtsNext(sqlite3_vtab_cursor *cur){
stmts_cursor *pCur = (stmts_cursor*)cur;
pCur->iRowid++;
pCur->pStmt = sqlite3_next_stmt(pCur->db, pCur->pStmt);
return SQLITE_OK;
}
/*
** Return values of columns for the row at which the stmts_cursor
** is currently pointing.
*/
static int stmtsColumn(
sqlite3_vtab_cursor *cur, /* The cursor */
sqlite3_context *ctx, /* First argument to sqlite3_result_...() */
int i /* Which column to return */
){
stmts_cursor *pCur = (stmts_cursor*)cur;
switch( i ){
case STMTS_COLUMN_PTR: {
sqlite3_result_int64(ctx, SQLITE_PTR_TO_INT64(pCur->pStmt));
break;
}
case STMTS_COLUMN_SQL: {
sqlite3_result_text(ctx, sqlite3_sql(pCur->pStmt), -1, SQLITE_TRANSIENT);
break;
}
case STMTS_COLUMN_NCOL: {
sqlite3_result_int(ctx, sqlite3_column_count(pCur->pStmt));
break;
}
case STMTS_COLUMN_RO: {
sqlite3_result_int(ctx, sqlite3_stmt_readonly(pCur->pStmt));
break;
}
case STMTS_COLUMN_BUSY: {
sqlite3_result_int(ctx, sqlite3_stmt_busy(pCur->pStmt));
break;
}
case STMTS_COLUMN_NSCAN:
case STMTS_COLUMN_NSORT:
case STMTS_COLUMN_NAIDX:
case STMTS_COLUMN_NSTEP: {
sqlite3_result_int(ctx, sqlite3_stmt_status(pCur->pStmt,
i-STMTS_COLUMN_NSCAN+SQLITE_STMTSTATUS_FULLSCAN_STEP, 0));
break;
}
}
return SQLITE_OK;
}
/*
** Return the rowid for the current row. In this implementation, the
** rowid is the same as the output value.
*/
static int stmtsRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
stmts_cursor *pCur = (stmts_cursor*)cur;
*pRowid = pCur->iRowid;
return SQLITE_OK;
}
/*
** Return TRUE if the cursor has been moved off of the last
** row of output.
*/
static int stmtsEof(sqlite3_vtab_cursor *cur){
stmts_cursor *pCur = (stmts_cursor*)cur;
return pCur->pStmt==0;
}
/*
** This method is called to "rewind" the stmts_cursor object back
** to the first row of output. This method is always called at least
** once prior to any call to stmtsColumn() or stmtsRowid() or
** stmtsEof().
*/
static int stmtsFilter(
sqlite3_vtab_cursor *pVtabCursor,
int idxNum, const char *idxStr,
int argc, sqlite3_value **argv
){
stmts_cursor *pCur = (stmts_cursor *)pVtabCursor;
pCur->pStmt = 0;
pCur->iRowid = 0;
return stmtsNext(pVtabCursor);
}
/*
** SQLite will invoke this method one or more times while planning a query
** that uses the generate_stmts virtual table. This routine needs to create
** a query plan for each invocation and compute an estimated cost for that
** plan.
*/
static int stmtsBestIndex(
sqlite3_vtab *tab,
sqlite3_index_info *pIdxInfo
){
pIdxInfo->estimatedCost = (double)500;
pIdxInfo->estimatedRows = 500;
return SQLITE_OK;
}
/*
** This following structure defines all the methods for the
** generate_stmts virtual table.
*/
static sqlite3_module stmtsModule = {
0, /* iVersion */
0, /* xCreate */
stmtsConnect, /* xConnect */
stmtsBestIndex, /* xBestIndex */
stmtsDisconnect, /* xDisconnect */
0, /* xDestroy */
stmtsOpen, /* xOpen - open a cursor */
stmtsClose, /* xClose - close a cursor */
stmtsFilter, /* xFilter - configure scan constraints */
stmtsNext, /* xNext - advance a cursor */
stmtsEof, /* xEof - check for end of scan */
stmtsColumn, /* xColumn - read data */
stmtsRowid, /* xRowid - read data */
0, /* xUpdate */
0, /* xBegin */
0, /* xSync */
0, /* xCommit */
0, /* xRollback */
0, /* xFindMethod */
0, /* xRename */
};
#endif /* SQLITE_OMIT_VIRTUALTABLE */
#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_stmts_init(
sqlite3 *db,
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
#ifndef SQLITE_OMIT_VIRTUALTABLE
if( sqlite3_libversion_number()<3008012 ){
*pzErrMsg = sqlite3_mprintf(
"generate_stmts() requires SQLite 3.8.12 or later");
return SQLITE_ERROR;
}
rc = sqlite3_create_module(db, "stmts", &stmtsModule, 0);
#endif
return rc;
}