@Override
    public Object get( String key ){
        if ( key == null )
            throw new RuntimeException( "key should never be null" );
        else if ( key.equals( "_id" ) )
            return _id;
        else if ( key.equals( "filename" ) )
            return _filename;
        else if ( key.equals( "contentType" ) )
            return _contentType;
        else if ( key.equals( "length" ) )
            return _length;
        else if ( key.equals( "chunkSize" ) )
            return _chunkSize;
        else if ( key.equals( "uploadDate" ) )
            return _uploadDate;
        else if ( key.equals( "md5" ) )
            return _md5;
        return _extradata.get( key );
    }