From b97073ee1892099c57b8720ed909cd348c5daf43 Mon Sep 17 00:00:00 2001
From: "byte[]" <byteslice@airmail.cc>
Date: Mon, 13 Jul 2020 23:44:45 -0400
Subject: [PATCH] reintroduce transaction and add impossible condition to first
 element of reduce step

---
 lib/philomena/tag_changes.ex | 75 ++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 34 deletions(-)

diff --git a/lib/philomena/tag_changes.ex b/lib/philomena/tag_changes.ex
index 6580799b..0f7d2a00 100644
--- a/lib/philomena/tag_changes.ex
+++ b/lib/philomena/tag_changes.ex
@@ -37,59 +37,66 @@ defmodule Philomena.TagChanges do
     to_remove =
       added
       |> Enum.map(&{&1.image_id, &1.tag_id})
-      |> Enum.reduce(Tagging, fn {image_id, tag_id}, q ->
+      |> Enum.reduce(where(Tagging, fragment("'t' = 'f'")), fn {image_id, tag_id}, q ->
         or_where(q, image_id: ^image_id, tag_id: ^tag_id)
       end)
       |> select([t], [t.image_id, t.tag_id])
 
     to_add = Enum.map(removed, &%{image_id: &1.image_id, tag_id: &1.tag_id})
 
-    {_count, inserted} =
-      Repo.insert_all(Tagging, to_add, on_conflict: :nothing, returning: [:image_id, :tag_id])
+    Repo.transaction(fn ->
+      {_count, inserted} =
+        Repo.insert_all(Tagging, to_add, on_conflict: :nothing, returning: [:image_id, :tag_id])
 
-    {_count, deleted} = Repo.delete_all(to_remove)
+      {_count, deleted} = Repo.delete_all(to_remove)
 
-    inserted = Enum.map(inserted, &[&1.image_id, &1.tag_id])
+      inserted = Enum.map(inserted, &[&1.image_id, &1.tag_id])
 
-    added_changes =
-      Enum.map(inserted, fn [image_id, tag_id] ->
-        Map.merge(tag_change_attributes, %{image_id: image_id, tag_id: tag_id, added: true})
-      end)
+      added_changes =
+        Enum.map(inserted, fn [image_id, tag_id] ->
+          Map.merge(tag_change_attributes, %{image_id: image_id, tag_id: tag_id, added: true})
+        end)
 
-    removed_changes =
-      Enum.map(deleted, fn [image_id, tag_id] ->
-        Map.merge(tag_change_attributes, %{image_id: image_id, tag_id: tag_id, added: false})
-      end)
+      removed_changes =
+        Enum.map(deleted, fn [image_id, tag_id] ->
+          Map.merge(tag_change_attributes, %{image_id: image_id, tag_id: tag_id, added: false})
+        end)
 
-    Repo.insert_all(TagChange, added_changes ++ removed_changes)
+      Repo.insert_all(TagChange, added_changes ++ removed_changes)
 
-    # In order to merge into the existing tables here in one go, insert_all
-    # is used with a query that is guaranteed to conflict on every row by
-    # using the primary key.
+      # In order to merge into the existing tables here in one go, insert_all
+      # is used with a query that is guaranteed to conflict on every row by
+      # using the primary key.
 
-    added_upserts =
-      inserted
-      |> Enum.group_by(fn [_image_id, tag_id] -> tag_id end)
-      |> Enum.map(fn {tag_id, instances} ->
-        Map.merge(tag_attributes, %{id: tag_id, images_count: length(instances)})
-      end)
+      added_upserts =
+        inserted
+        |> Enum.group_by(fn [_image_id, tag_id] -> tag_id end)
+        |> Enum.map(fn {tag_id, instances} ->
+          Map.merge(tag_attributes, %{id: tag_id, images_count: length(instances)})
+        end)
 
-    removed_upserts =
-      deleted
-      |> Enum.group_by(fn [_image_id, tag_id] -> tag_id end)
-      |> Enum.map(fn {tag_id, instances} ->
-        Map.merge(tag_attributes, %{id: tag_id, images_count: -length(instances)})
-      end)
+      removed_upserts =
+        deleted
+        |> Enum.group_by(fn [_image_id, tag_id] -> tag_id end)
+        |> Enum.map(fn {tag_id, instances} ->
+          Map.merge(tag_attributes, %{id: tag_id, images_count: -length(instances)})
+        end)
 
-    update_query = update(Tag, inc: [images_count: fragment("EXCLUDED.images_count")])
+      update_query = update(Tag, inc: [images_count: fragment("EXCLUDED.images_count")])
 
-    upserts = added_upserts ++ removed_upserts
+      upserts = added_upserts ++ removed_upserts
 
-    Repo.insert_all(Tag, upserts, on_conflict: update_query, conflict_target: [:id])
+      Repo.insert_all(Tag, upserts, on_conflict: update_query, conflict_target: [:id])
+    end)
+    |> case do
+      {:ok, _result} ->
+        Images.reindex_images(image_ids)
 
-    Images.reindex_images(image_ids)
+        {:ok, tag_changes}
 
-    {:ok, tag_changes}
+      error ->
+        error
+    end
   end
 
   @doc """