Add CreateFollowingRelationships migration

priv/repo/migrations/20191007073319_create_following_relationships.exs

@@ -0,0 +1,92 @@
+defmodule Pleroma.Repo.Migrations.CreateFollowingRelationships do
+  use Ecto.Migration
+
+  # had to disable these to be able to restore `following` index concurrently
+  # https://hexdocs.pm/ecto_sql/Ecto.Migration.html#index/3-adding-dropping-indexes-concurrently
+  @disable_ddl_transaction true
+  @disable_migration_lock true
+
+  def change do
+    create_if_not_exists table(:following_relationships) do
+      add(:follower_id, references(:users, type: :uuid, on_delete: :delete_all), null: false)
+      add(:following_id, references(:users, type: :uuid, on_delete: :delete_all), null: false)
+      add(:state, :string, null: false)
+
+      timestamps()
+    end
+
+    create_if_not_exists(index(:following_relationships, :follower_id))
+    create_if_not_exists(unique_index(:following_relationships, [:follower_id, :following_id]))
+
+    execute(insert_following_relationships_rows(), restore_following_column())
+
+    drop(index(:users, [:following], concurrently: true, using: :gin))
+
+    alter table(:users) do
+      remove(:following, {:array, :string}, default: [])
+    end
+  end
+
+  defp insert_following_relationships_rows do
+    """
+    INSERT INTO
+        following_relationships (
+            follower_id,
+            following_id,
+            state,
+            inserted_at,
+            updated_at
+        )
+    SELECT
+        followers.id,
+        following.id,
+        activities.data ->> 'state',
+        (activities.data ->> 'published') :: timestamp,
+        now()
+    FROM
+        activities
+        JOIN users AS followers ON (activities.actor = followers.ap_id)
+        JOIN users AS following ON (activities.data ->> 'object' = following.ap_id)
+    WHERE
+        activities.data ->> 'type' = 'Follow'
+        AND activities.data ->> 'state' IN ('accept', 'pending', 'reject') ON CONFLICT DO NOTHING
+    """
+  end
+
+  defp restore_following_column do
+    """
+    UPDATE
+        users
+    SET
+        following = following_query.following,
+        updated_at = now()
+    FROM
+        (
+            SELECT
+                followers.id AS follower_id,
+                array_prepend(
+                    followers.follower_address,
+                    array_agg(DISTINCT following.ap_id) FILTER (
+                        WHERE
+                            following.ap_id IS NOT NULL
+                    )
+                ) as following
+            FROM
+                users AS followers
+                LEFT OUTER JOIN activities ON (
+                    followers.ap_id = activities.actor
+                    AND activities.data ->> 'type' = 'Follow'
+                    AND activities.data ->> 'state' IN ('accept', 'pending', 'reject')
+                )
+                LEFT OUTER JOIN users AS following ON (activities.data ->> 'object' = following.ap_id)
+            WHERE
+                followers.email IS NOT NULL  -- Exclude `internal/fetch` and `relay`
+            GROUP BY
+                followers.id,
+                followers.ap_id
+        ) AS following_query
+    WHERE
+        following_query.follower_id = users.id;
+    """
+  end
+end