You can get all those in one fell swoop with nested preloads.
cms_learn_post -> cms_learn_headlines -> cms_learn_category -> cms_learn_headlines
An equivalent example with
Track -> Album -> Artist -> Album
iex(1)> alias MusicDB.{Repo,Album,Track}
[MusicDB.Repo, MusicDB.Album, MusicDB.Track]
iex(2)> import Ecto.Query
Ecto.Query
iex(3)> track_id = 29
29
iex(4)> query = from(t in Track, [
...(4)> preload: [{:album,[{:artist,:albums}]}],
...(4)> where: t.id == ^track_id
...(4)> ])
#Ecto.Query<from t in MusicDB.Track, where: t.id == ^29,
preload: [album: [artist: [:albums]]]>
iex(5)> Repo.all(query)
17:24:06.532 [debug] QUERY OK source="tracks" db=2.4ms decode=1.6ms
SELECT t0."id", t0."title", t0."duration", t0."index", t0."number_of_plays", t0."inserted_at", t0."updated_at", t0."album_id" FROM "tracks" AS t0 WHERE (t0."id" = $1) [29]
17:24:06.538 [debug] QUERY OK source="albums" db=1.6ms
SELECT a0."id", a0."title", a0."inserted_at", a0."updated_at", a0."artist_id", a0."id" FROM "albums" AS a0 WHERE (a0."id" = $1) [4]
17:24:06.540 [debug] QUERY OK source="artists" db=0.8ms
SELECT a0."id", a0."name", a0."birth_date", a0."death_date", a0."inserted_at", a0."updated_at", a0."id" FROM "artists" AS a0 WHERE (a0."id" = $1) [2]
17:24:06.543 [debug] QUERY OK source="albums" db=1.8ms
SELECT a0."id", a0."title", a0."inserted_at", a0."updated_at", a0."artist_id", a0."artist_id" FROM "albums" AS a0 WHERE (a0."artist_id" = $1) ORDER BY a0."artist_id" [2]
[
%MusicDB.Track{
__meta__: #Ecto.Schema.Metadata<:loaded, "tracks">,
album: %MusicDB.Album{
__meta__: #Ecto.Schema.Metadata<:loaded, "albums">,
artist: %MusicDB.Artist{
__meta__: #Ecto.Schema.Metadata<:loaded, "artists">,
albums: [
%MusicDB.Album{
__meta__: #Ecto.Schema.Metadata<:loaded, "albums">,
artist: #Ecto.Association.NotLoaded<association :artist is not loaded>,
artist_id: 2,
genres: #Ecto.Association.NotLoaded<association :genres is not loaded>,
id: 4,
inserted_at: ~N[2018-06-16 20:29:41.493342],
title: "Portrait In Jazz",
tracks: #Ecto.Association.NotLoaded<association :tracks is not loaded>,
updated_at: ~N[2018-06-16 20:29:41.493348]
},
%MusicDB.Album{
__meta__: #Ecto.Schema.Metadata<:loaded, "albums">,
artist: #Ecto.Association.NotLoaded<association :artist is not loaded>,
artist_id: 2,
genres: #Ecto.Association.NotLoaded<association :genres is not loaded>,
id: 3,
inserted_at: ~N[2018-06-16 20:29:41.483682],
title: "You Must Believe In Spring",
tracks: #Ecto.Association.NotLoaded<association :tracks is not loaded>,
updated_at: ~N[2018-06-16 20:29:41.483713]
}
],
birth_date: nil,
death_date: nil,
id: 2,
inserted_at: ~N[2018-06-16 20:29:41.481934],
name: "Bill Evans",
tracks: #Ecto.Association.NotLoaded<association :tracks is not loaded>,
updated_at: ~N[2018-06-16 20:29:41.481940]
},
artist_id: 2,
genres: #Ecto.Association.NotLoaded<association :genres is not loaded>,
id: 4,
inserted_at: ~N[2018-06-16 20:29:41.493342],
title: "Portrait In Jazz",
tracks: #Ecto.Association.NotLoaded<association :tracks is not loaded>,
updated_at: ~N[2018-06-16 20:29:41.493348]
},
album_id: 4,
duration: 325,
duration_string: nil,
id: 29,
index: 9,
inserted_at: ~N[2018-06-16 20:29:41.499008],
number_of_plays: 0,
title: "Blue In Green",
updated_at: ~N[2018-06-16 20:29:41.499013]
}
]
iex(6)>
