presto-mongodb/src/main/java/io/prestosql/plugin/mongodb/MongoPageSourceProvider.java/MongoPageSourceProvider/createPageSource
class MongoPageSourceProvider:    @Override
    public ConnectorPageSource createPageSource(ConnectorTransactionHandle transaction, ConnectorSession session, ConnectorSplit split, ConnectorTableHandle table, List<ColumnHandle> columns)
    {
        MongoTableHandle tableHandle = (MongoTableHandle) table;

        ImmutableList.Builder<MongoColumnHandle> handles = ImmutableList.builder();
        for (ColumnHandle handle : requireNonNull(columns, "columns is null")) {
            handles.add((MongoColumnHandle) handle);
        }

        return new MongoPageSource(mongoSession, tableHandle, handles.build());
    }