I’m doing a fairly complex join where I want to preload an array of ContentMediaItems (called :contents) that are nested in an association, Channel

But it appears that ecto thinks I’m referencing the MediaItem in the preload even though I’m doing:

preload: [channel: {chan, contents: chancon}],

and name the associations previously:

join: chan in assoc(con, :channel),
join: chancon in assoc(chan, :contents),

So why does the exception

    ** (Ecto.QueryError) field `MyWord.Multimedia.MediaItem.channel` in preload is not an association in query:

appear?

Here is the full query along with the error below it.

    from(m in MediaItem,
      join: con in ContentMediaItems,
      on: m.id == con.media_item_id,
      where: is_nil(m.published_at) == false,
      join: chan in assoc(con, :channel),
      where: chan.id == con.channel_id,
      join: chancon in assoc(chan, :contents),
      on: chancon.channel_id == chan.id,
      join: org in Org,
      on: m.org_id == org.id,
      where: org.slug == ^org_slug,
      order_by: [{:desc, :published_at}],
      preload: [:mediaitemartifacts],
      preload: [channel: {chan, contents: chancon}],
      select: %{id: m.id, inserted_at: m.inserted_at, media_item: m, channel: chan}
    )

Exception:

** (Ecto.QueryError) field `MyWord.Multimedia.MediaItem.channel` in preload is not an association in query:

from m0 in MyWord.Multimedia.MediaItem,
  join: c1 in MyWord.Channels.ContentMediaItems,
  on: m0.id == c1.media_item_id,
  join: c2 in MyWord.Channels.Channel,
  on: c2.id == c1.channel_id,
  join: c3 in MyWord.Channels.ContentMediaItems,
  on: c3.channel_id == c2.id and c3.channel_id == c2.id,
  join: o4 in MyWord.Orgs.Org,
  on: m0.org_id == o4.id,
  where: is_nil(m0.published_at) == false,
  where: c2.id == c1.channel_id,
  where: o4.slug == ^"myword-app",
  order_by: [desc: m0.published_at],
  limit: ^41,
  select: %{id: m0.id, inserted_at: m0.inserted_at, media_item: m0, channel: c2},
  preload: [:mediaitemartifacts],
  preload: [channel: {c2, contents: c3}]

Relevant schema information:

schema "mediaitems" do
    has_many(:mediaitemartifacts, MyWord.Multimedia.MediaItemArtifact)
    many_to_many(:channels, Channel, join_through: "channels_content_media_items", unique: true)

schema "channels" do
  has_many(:contents, ContentMediaItems)

schema "channels_content_media_items" do
  belongs_to :channel, Channel
  belongs_to :media_item, MediaItem