prepare method

Implementation

void prepare() {
  if (prepared) return;
  if (_database == null) {
    databaseError(SErrDatabasenAssigned);
  }
  if (_transaction == null) {
    databaseError(SErrTransactionnSet);
  }
  database!.maybeConnect();
  if (!transaction!.active) {
    transaction!.maybeStartTransaction();
  }
  try {
    doPrepare();
  } catch (_) {
    deAllocateCursor();
    rethrow;
  }
}