How to swap which table is returned in Ecto?

Background

I have a a couple of queries that result in the archival of some metadata items. My objective is to merge these queries into one (if possible).

Code

meta_item_ids_to_archive =
      Post
      |> where([post], post.archive_meta)
      |> select([post], %{item_id: post.meta_id})
      |> subquery()

archive_meta_items_query =
      Meta
      |> join(:inner, [item], item_to_archive in ^meta_item_ids_to_archive,
        on: item.id == item_to_archive.item_id
      )

########
later on
########

Multi.update_all(
  :query_a, 
  archive_meta_items_query, 
  set: [archived: true]
)

So my original query starts with Post and then int eh subsequent query I start with Meta. I want to archive items in the Meta table. My first attempt at merging these queries was the following:

new_query = 
  Post
  |> where([post], post.archive_meta)
  |> join(:inner, [post], item_to_archive in Meta,
        on: post.meta_id == item_to_archive.item_id
  )

Multi.update_all(
  :query_a, 
  new_query, 
  set: [archived: true]
)

Problem

Now, the issue here is that this won’t work:

field archived in update does not exist in schema Post in query (…):

Because my new_query starts with Post instead of Meta, the update operation fails.

Question

• Is there a way to tell Ecto “I want the Meta table returned instead of Post?”
• If now, how can I solve this?