SQLite copy database destroyed original, Why? - c++

Question

I got this code snippet to copy a file database to a memory database. it works but it destroys the original file database. (By destroys I mean sets the file size to zero)
/**
* Exec an sql statement in values[0] against
* the database in pData.
*/
int process_ddl_row(void * pData, int nColumns, char **values, char **columns)
{
if (nColumns != 1) {
return 1; // Error
}
sqlite3 * db = (sqlite3*)pData;
if( SQLITE_OK != sqlite3_exec(db, values[0], NULL, NULL, NULL) ) {
return 1;
}
return 0;
}
/**
* Insert from a table named by backup.{values[0]}
* into main.{values[0]} in database pData.
*/
int process_dml_row(void *pData, int nColumns, char **values, char **columns)
{
if (nColumns != 1) {
return 1; // Error
}
sqlite3* db = (sqlite3*)pData;
char *stmt = sqlite3_mprintf("insert into main.%q " "select * from backup.%q", values[0], values[0]);
if( SQLITE_OK != sqlite3_exec(db, stmt, NULL, NULL, NULL) ) {
return 1;
}
sqlite3_free(stmt);
return 0;
}
bool CDatabase::LoadFromFile( const char * databaseFile )
{
if( databaseFile == NULL || this->m_db == NULL ) {
return false;
}
sqlite3 * memorydb = this->m_db->GetDb() ; // Gets the open memory database.
sqlite3 * backupdb = NULL ;
if( SQLITE_OK != sqlite3_open_v2(databaseFile, &backupdb, SQLITE_OPEN_READONLY, NETBURNER_VFS_NAME ) ) {
return false;
}
// Schema
// ---------------------------------------------------------------------------
// Create the in-memory schema from the backup
if( SQLITE_OK != sqlite3_exec(backupdb, "BEGIN", NULL, NULL, NULL) ) {
return false;
}
if( SQLITE_OK != sqlite3_exec(backupdb, "SELECT sql FROM sqlite_master WHERE sql NOT NULL", &process_ddl_row, memorydb, NULL) ) {
return false;
}
if( SQLITE_OK != sqlite3_exec(backupdb, "COMMIT", NULL, NULL, NULL) ) {
return false;
}
sqlite3_close(backupdb);
// DATA
// ---------------------------------------------------------------------------
// Attach the backup to the in memory
char sql[255];
sprintf( sql, "ATTACH DATABASE '%s' as backup", databaseFile );
// This after this line the file database is set to zero bytes.
if( SQLITE_OK != sqlite3_exec(memorydb, sql, NULL, NULL, NULL) ) {
return false;
}
// Copy the data from the backup to the in memory
if( SQLITE_OK != sqlite3_exec(memorydb, "BEGIN", NULL, NULL, NULL) ) {
return false;
}
if( SQLITE_OK != sqlite3_exec(memorydb, "SELECT name FROM backup.sqlite_master WHERE type='table'", &process_dml_row, memorydb, NULL) ) {
return false;
}
if( SQLITE_OK != sqlite3_exec(memorydb, "COMMIT", NULL, NULL, NULL) ) {
return false;
}
if( SQLITE_OK != sqlite3_exec(memorydb, "DETACH DATABASE backup", NULL, NULL, NULL) ) {
return false;
}
return true;
}
I have been looking at it for awhile now and I can seem to figure out why this is happening. Suggestions?

Answer 1

Your code worked fine for me (checked on WinXP).
I think you should try running it without specifying VFS object (if possible) - just replace NETBURNER_VFS_NAME with 0 in sqlite3_open_v2 call.
This will show whether the problem is in VFS customization or not.