CODEWITHSUNDEEP
qtsqlite
Robert
Robert

Reputation: 1343

Import SQLite database using Qt/QSqlDatabase

I have two separate applications, one placed at the production another at an office, and I need to get a copy of an sqlite database generated and updated at production side.

Until now I've tried two approches:

  1. Copy the entire sqlite file from the production-application and "redirect" my QSqlDatabase-handles to that file (was not able to get it to work, many connections are already opened and not all closable)
  2. Access the sqlite-db over network, query all data and insert the missing data using sql (works, but since there is a lot of data it takes too much time)

Are there possibilities to import or maybe override an existing database (or even single tables, placed in different files), where there are still open connections?

Using: Qt 4.8, SQLite, Windows 7, VS2010

Upvotes: 0

Views: 1967

Answers (1)

Robert
Robert

Reputation: 1343

So finally I was able to reach my goal by using the sqlite backup api (which is distributed as .h and .c with most Qt versions). On the documentation page SQLite Backup there are a few examples, where a database is copied either from a file to an in-memory db, or from an in-memory to a file. In my case I used the following function (1:1 from doc page, only several comments removed):

int loadOrSaveDb(sqlite3 *pInMemory, const char *zFilename, int isSave){
  int rc;                   /* Function return code */
  sqlite3 *pFile;           /* Database connection opened on zFilename */
  sqlite3_backup *pBackup;  /* Backup object used to copy data */
  sqlite3 *pTo;             /* Database to copy to (pFile or pInMemory) */
  sqlite3 *pFrom;           /* Database to copy from (pFile or pInMemory) */

  /* Open the database file identified by zFilename. Exit early if this fails
  ** for any reason. */
  rc = sqlite3_open(zFilename, &pFile);
  if( rc==SQLITE_OK ){

    pFrom = (isSave ? pInMemory : pFile);
    pTo   = (isSave ? pFile     : pInMemory);

    pBackup = sqlite3_backup_init(pTo, "main", pFrom, "main");
    if( pBackup ){
      (void)sqlite3_backup_step(pBackup, -1);
      (void)sqlite3_backup_finish(pBackup);
    }
    rc = sqlite3_errcode(pTo);
  }

  (void)sqlite3_close(pFile);
  return rc;
}

The only additional steps to get the handle needed in the function above were:

1.Get sqlite-handle from QSqlDatabase

QVariant destVar = database.driver()->handle();

2.Check handle for validity and cast to sqlite3*

if(destVar.isValid() && qstrcmp(destVar.typeName(), "sqlite3*") == 0)
{
    sqlite3* destination = *static_cast<sqlite3 **>(destVar.data());
    ...
}

Thanks to CL. (who was pointing the right direction).

Upvotes: 1

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