Fix #4901: Duplicate disapprovals

* Add uniqueness constraint on post_disapprovals (user_id, post_id).
* Add fix script to remove existing duplicates.

app/models/application_record.rb

@@ -145,6 +145,29 @@ class ApplicationRecord < ActiveRecord::Base
       def update!(*args)
         all.each { |record| record.update!(*args) }
       end
+
+      def each_duplicate(*columns)
+        return enum_for(:each_duplicate, *columns) unless block_given?
+
+        group(columns).having("count(*) > 1").count.each do |values, count|
+          hash = columns.zip(Array.wrap(values)).to_h
+          yield count: count, **hash
+        end
+      end
+
+      def destroy_duplicates!(*columns, log: true)
+        each_duplicate(*columns) do |count:, **columns_with_values|
+          records = where(columns_with_values).order(:id)
+          dupes = records.drop(1)
+
+          if log
+            data = { keep: records.first.id, destroy: dupes.map(&:id), count: count, **columns_with_values }
+            DanbooruLogger.info("Destroying duplicate #{self.name} #{dupes.map(&:id).join(", ")}", data)
+          end
+
+          dupes.each(&:destroy!)
+        end
+      end
     end
   end
 

db/migrate/20211013011619_add_unique_user_id_and_post_id_index_to_post_disapprovals.rb

@@ -0,0 +1,5 @@
+class AddUniqueUserIdAndPostIdIndexToPostDisapprovals < ActiveRecord::Migration[6.1]
+  def change
+    add_index :post_disapprovals, [:user_id, :post_id], unique: true
+  end
+end

db/structure.sql

@@ -4096,6 +4096,13 @@ CREATE INDEX index_post_disapprovals_on_post_id ON public.post_disapprovals USIN
 CREATE INDEX index_post_disapprovals_on_user_id ON public.post_disapprovals USING btree (user_id);
 
 
+--
+-- Name: index_post_disapprovals_on_user_id_and_post_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE UNIQUE INDEX index_post_disapprovals_on_user_id_and_post_id ON public.post_disapprovals USING btree (user_id, post_id);
+
+
 --
 -- Name: index_post_flags_on_creator_id; Type: INDEX; Schema: public; Owner: -
 --
@@ -5060,6 +5067,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20210926125826'),
 ('20211008091234'),
 ('20211010181657'),
-('20211011044400');
+('20211011044400'),
+('20211013011619');
 
 

script/fixes/081_delete_duplicate_post_disapprovals.rb

@@ -0,0 +1,7 @@
+#!/usr/bin/env ruby
+
+require_relative "../../config/environment"
+
+PostDisapproval.transaction do
+  PostDisapproval.destroy_duplicates!(:user_id, :post_id)
+end

test/unit/application_record.rb

@@ -45,4 +45,20 @@ class ApplicationRecordTest < ActiveSupport::TestCase
       end
     end
   end
+
+  context "ApplicationRecord#destroy_duplicates!" do
+    should "destroy all duplicates" do
+      @post1 = create(:post, score: 42)
+      @post2 = create(:post, score: 42)
+      @post3 = create(:post, score: 42)
+      @post4 = create(:post, score: 23)
+
+      Post.destroy_duplicates!(:score)
+
+      assert_equal(true,  Post.exists?(@post1.id))
+      assert_equal(false, Post.exists?(@post2.id))
+      assert_equal(false, Post.exists?(@post3.id))
+      assert_equal(true,  Post.exists?(@post4.id))
+    end
+  end
 end