| /* |
| ** 2018-04-19 |
| ** |
| ** 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 implements a template virtual-table. |
| ** Developers can make a copy of this file as a baseline for writing |
| ** new virtual tables and/or table-valued functions. |
| ** |
| ** Steps for writing a new virtual table implementation: |
| ** |
| ** (1) Make a copy of this file. Perhaps call it "mynewvtab.c" |
| ** |
| ** (2) Replace this header comment with something appropriate for |
| ** the new virtual table |
| ** |
| ** (3) Change every occurrence of "templatevtab" to some other string |
| ** appropriate for the new virtual table. Ideally, the new string |
| ** should be the basename of the source file: "mynewvtab". Also |
| ** globally change "TEMPLATEVTAB" to "MYNEWVTAB". |
| ** |
| ** (4) Run a test compilation to make sure the unmodified virtual |
| ** table works. |
| ** |
| ** (5) Begin making incremental changes, testing as you go, to evolve |
| ** the new virtual table to do what you want it to do. |
| ** |
| ** This template is minimal, in the sense that it uses only the required |
| ** methods on the sqlite3_module object. As a result, templatevtab is |
| ** a read-only and eponymous-only table. Those limitation can be removed |
| ** by adding new methods. |
| ** |
| ** This template implements an eponymous-only virtual table with a rowid and |
| ** two columns named "a" and "b". The table as 10 rows with fixed integer |
| ** values. Usage example: |
| ** |
| ** SELECT rowid, a, b FROM templatevtab; |
| */ |
| #if !defined(SQLITEINT_H) |
| #include "sqlite3ext.h" |
| #endif |
| SQLITE_EXTENSION_INIT1 |
| #include <string.h> |
| #include <assert.h> |
| |
| /* templatevtab_vtab is a subclass of sqlite3_vtab which is |
| ** underlying representation of the virtual table |
| */ |
| typedef struct templatevtab_vtab templatevtab_vtab; |
| struct templatevtab_vtab { |
| sqlite3_vtab base; /* Base class - must be first */ |
| /* Add new fields here, as necessary */ |
| }; |
| |
| /* templatevtab_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 templatevtab_cursor templatevtab_cursor; |
| struct templatevtab_cursor { |
| sqlite3_vtab_cursor base; /* Base class - must be first */ |
| /* Insert new fields here. For this templatevtab we only keep track |
| ** of the rowid */ |
| sqlite3_int64 iRowid; /* The rowid */ |
| }; |
| |
| /* |
| ** The templatevtabConnect() method is invoked to create a new |
| ** template virtual table. |
| ** |
| ** Think of this routine as the constructor for templatevtab_vtab objects. |
| ** |
| ** All this routine needs to do is: |
| ** |
| ** (1) Allocate the templatevtab_vtab object and initialize all fields. |
| ** |
| ** (2) Tell SQLite (via the sqlite3_declare_vtab() interface) what the |
| ** result set of queries against the virtual table will look like. |
| */ |
| static int templatevtabConnect( |
| sqlite3 *db, |
| void *pAux, |
| int argc, const char *const*argv, |
| sqlite3_vtab **ppVtab, |
| char **pzErr |
| ){ |
| templatevtab_vtab *pNew; |
| int rc; |
| |
| rc = sqlite3_declare_vtab(db, |
| "CREATE TABLE x(a,b)" |
| ); |
| /* For convenience, define symbolic names for the index to each column. */ |
| #define TEMPLATEVTAB_A 0 |
| #define TEMPLATEVTAB_B 1 |
| if( rc==SQLITE_OK ){ |
| pNew = sqlite3_malloc( sizeof(*pNew) ); |
| *ppVtab = (sqlite3_vtab*)pNew; |
| if( pNew==0 ) return SQLITE_NOMEM; |
| memset(pNew, 0, sizeof(*pNew)); |
| } |
| return rc; |
| } |
| |
| /* |
| ** This method is the destructor for templatevtab_vtab objects. |
| */ |
| static int templatevtabDisconnect(sqlite3_vtab *pVtab){ |
| templatevtab_vtab *p = (templatevtab_vtab*)pVtab; |
| sqlite3_free(p); |
| return SQLITE_OK; |
| } |
| |
| /* |
| ** Constructor for a new templatevtab_cursor object. |
| */ |
| static int templatevtabOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor){ |
| templatevtab_cursor *pCur; |
| pCur = sqlite3_malloc( sizeof(*pCur) ); |
| if( pCur==0 ) return SQLITE_NOMEM; |
| memset(pCur, 0, sizeof(*pCur)); |
| *ppCursor = &pCur->base; |
| return SQLITE_OK; |
| } |
| |
| /* |
| ** Destructor for a templatevtab_cursor. |
| */ |
| static int templatevtabClose(sqlite3_vtab_cursor *cur){ |
| templatevtab_cursor *pCur = (templatevtab_cursor*)cur; |
| sqlite3_free(pCur); |
| return SQLITE_OK; |
| } |
| |
| |
| /* |
| ** Advance a templatevtab_cursor to its next row of output. |
| */ |
| static int templatevtabNext(sqlite3_vtab_cursor *cur){ |
| templatevtab_cursor *pCur = (templatevtab_cursor*)cur; |
| pCur->iRowid++; |
| return SQLITE_OK; |
| } |
| |
| /* |
| ** Return values of columns for the row at which the templatevtab_cursor |
| ** is currently pointing. |
| */ |
| static int templatevtabColumn( |
| sqlite3_vtab_cursor *cur, /* The cursor */ |
| sqlite3_context *ctx, /* First argument to sqlite3_result_...() */ |
| int i /* Which column to return */ |
| ){ |
| templatevtab_cursor *pCur = (templatevtab_cursor*)cur; |
| switch( i ){ |
| case TEMPLATEVTAB_A: |
| sqlite3_result_int(ctx, 1000 + pCur->iRowid); |
| break; |
| default: |
| assert( i==TEMPLATEVTAB_B ); |
| sqlite3_result_int(ctx, 2000 + pCur->iRowid); |
| 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 templatevtabRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){ |
| templatevtab_cursor *pCur = (templatevtab_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 templatevtabEof(sqlite3_vtab_cursor *cur){ |
| templatevtab_cursor *pCur = (templatevtab_cursor*)cur; |
| return pCur->iRowid>=10; |
| } |
| |
| /* |
| ** This method is called to "rewind" the templatevtab_cursor object back |
| ** to the first row of output. This method is always called at least |
| ** once prior to any call to templatevtabColumn() or templatevtabRowid() or |
| ** templatevtabEof(). |
| */ |
| static int templatevtabFilter( |
| sqlite3_vtab_cursor *pVtabCursor, |
| int idxNum, const char *idxStr, |
| int argc, sqlite3_value **argv |
| ){ |
| templatevtab_cursor *pCur = (templatevtab_cursor *)pVtabCursor; |
| pCur->iRowid = 1; |
| return SQLITE_OK; |
| } |
| |
| /* |
| ** SQLite will invoke this method one or more times while planning a query |
| ** that uses the virtual table. This routine needs to create |
| ** a query plan for each invocation and compute an estimated cost for that |
| ** plan. |
| */ |
| static int templatevtabBestIndex( |
| sqlite3_vtab *tab, |
| sqlite3_index_info *pIdxInfo |
| ){ |
| pIdxInfo->estimatedCost = (double)10; |
| pIdxInfo->estimatedRows = 10; |
| return SQLITE_OK; |
| } |
| |
| /* |
| ** This following structure defines all the methods for the |
| ** virtual table. |
| */ |
| static sqlite3_module templatevtabModule = { |
| /* iVersion */ 0, |
| /* xCreate */ 0, |
| /* xConnect */ templatevtabConnect, |
| /* xBestIndex */ templatevtabBestIndex, |
| /* xDisconnect */ templatevtabDisconnect, |
| /* xDestroy */ 0, |
| /* xOpen */ templatevtabOpen, |
| /* xClose */ templatevtabClose, |
| /* xFilter */ templatevtabFilter, |
| /* xNext */ templatevtabNext, |
| /* xEof */ templatevtabEof, |
| /* xColumn */ templatevtabColumn, |
| /* xRowid */ templatevtabRowid, |
| /* xUpdate */ 0, |
| /* xBegin */ 0, |
| /* xSync */ 0, |
| /* xCommit */ 0, |
| /* xRollback */ 0, |
| /* xFindMethod */ 0, |
| /* xRename */ 0, |
| /* xSavepoint */ 0, |
| /* xRelease */ 0, |
| /* xRollbackTo */ 0, |
| /* xShadowName */ 0 |
| }; |
| |
| |
| #ifdef _WIN32 |
| __declspec(dllexport) |
| #endif |
| int sqlite3_templatevtab_init( |
| sqlite3 *db, |
| char **pzErrMsg, |
| const sqlite3_api_routines *pApi |
| ){ |
| int rc = SQLITE_OK; |
| SQLITE_EXTENSION_INIT2(pApi); |
| rc = sqlite3_create_module(db, "templatevtab", &templatevtabModule, 0); |
| return rc; |
| } |