My issue

Hello, some time ago:

• I had the regular post and the custom evento post types;
• the evento post type had a ev_data_out custom field;
• the search result loop had to return a list of posts from both the post types (if relevant for the search), ordered by date;
• for post the considered field when ordering had to be the regular post_date, while for evento it had to be ev_data_out.

An example to clarify better.
These posts' dates:

PT "post"                PT "evento"
-----------------------  -------------------------
post_date = 2019-10-10   ev_data_out = 2020-11-10
post_date = 2017-03-12   ev_data_out = 2018-12-01

had to return a list ordered this way:

Results
--------------
2020-11-10
2019-10-10
2018-12-01
2017-03-12

My solution

Since my knowledge of Wp Query was (and is) still basic but I needed a fast implementation, I came out with this:

1. I hooked a function to post_save telling it to update_post_meta a post meta called order_date for each post type, with post_date's value if post and ev_data_out's value if evento;
2. I filtered pre_get_posts with a function that conditioned to if (is_search && !is_admin()) and setting $query -> set('meta_key', 'order_date'); and $query -> set('orderby', 'meta_value');

My question

So far I never had to retouch this stuff for it seems to work perfectly.

My question is, rather, if there is a method inherently better in Wordpress terms, i.e. if -with a better knowledge of the Wp Query, and of the meta queries in particular- I could get something more efficient and less DB-consuming.

N.b. I wish to understand things and not only to copy/paste, so an answer like "yes, study Wp Query better and you'll get the same result" would be perfectly fine for me!

Thanks!