Customize name of related entity ID

[XedinUnknown]

When retrieving related entities with WP_Query->query() by ID or set of IDs, the resulting entities will have the ID of the related entities set as the mb_origin property. This allows us to avoid having to query backwards for each entity. However, when returning the results, such as in a function e.g. get_answers_for_questions(), the consumer of such a function cannot know whether the entities were retrieved by mb-relationships, or in some other way, and therefore cannot rely on some generic mb_origin property.

It could be useful to be able to set a name for it. In my case, when I try to get Answer posts related to questions with the specified IDs, it would be useful if the Question ID of each Answer was under e.g. question_id. This could be as easy as changing the column alias name.

Also, if multiple Answers match each question ID, there will be more than one Answer in the result - each with a different mb_origin. It could be extremely useful to have the ability to have only unique Answers, but their e.g. question_ids parameter set to an array of IDs of related Questions.