In attach_story_data_to_stories(), don't overwrite existing fields

[pypt]

Hey Hal!

I know you're superbusy with other stuff, but could you have a quick look?

In #729 (and possibly #725), it looks like MediaWords::DBI::Stories::attach_story_data_to_stories() used to reset $list_field key to an empty arrayref on every call, thus making this subroutine not work when it was called multiple times, e.g. when data was being "attached" in chunks:

backend/apps/webapp-api/src/perl/MediaWords/Controller/Api/V2/StoriesBase.pm

Lines 279 to 302 in 12a0c0e

	my $iter = natatime(100, @{ $stories } );
	while ( my @chunk_stories = $iter->() )
	{
	my $chunk_ids_list = join( ',', map { int( $_->{ stories_id } ) } @chunk_stories );
	my $tag_data = $db->query(
	<<SQL
	SELECT
	s.stories_id::int,
	t.tags_id,
	t.tag,
	ts.tag_sets_id,
	ts.name AS tag_set
	FROM stories_tags_map AS s
	JOIN tags AS t
	ON t.tags_id = s.tags_id
	JOIN tag_sets AS ts
	ON ts.tag_sets_id = t.tag_sets_id
	WHERE stories_id in ( $chunk_ids_list )
	ORDER BY t.tags_id
	SQL
	)->hashes;
	$stories = MediaWords::DBI::Stories::attach_story_data_to_stories( $stories, $tag_data, 'story_tags' );
	}

I've now made the subroutine merge the input $story_data with whatever might already be in the parameter $stories under $list_field (if anything). There's also a test that verifies that the subroutine behaves as intended.

Does it look good to you?

[hroberts]

looks good to me. nice catch.