votes: add is_deleted flag to post_votes table.

Add an is_deleted flag to post_votes so they can be soft-deleted in the future.

app/models/post_vote.rb

@@ -12,6 +12,8 @@ class PostVote < ApplicationRecord
   scope :negative, -> { where("post_votes.score < 0") }
   scope :public_votes, -> { positive.where(user: User.has_public_favorites) }
 
+  deletable
+
   def self.visible(user)
     user.is_admin? ? all : where(user: user).or(public_votes)
   end

db/migrate/20211121080239_add_is_deleted_to_post_votes.rb

@@ -0,0 +1,9 @@
+class AddIsDeletedToPostVotes < ActiveRecord::Migration[6.1]
+  disable_ddl_transaction!
+
+  def change
+    add_column :post_votes, :is_deleted, :boolean, default: false, null: :false
+    add_index :post_votes, :is_deleted, where: "is_deleted = TRUE", algorithm: :concurrently
+    add_index :post_votes, [:user_id, :post_id], unique: true, where: "is_deleted = FALSE", algorithm: :concurrently
+  end
+end

db/structure.sql

@@ -1672,7 +1672,8 @@ CREATE TABLE public.post_votes (
     user_id integer NOT NULL,
     score integer NOT NULL,
     created_at timestamp without time zone NOT NULL,
-    updated_at timestamp without time zone NOT NULL
+    updated_at timestamp without time zone NOT NULL,
+    is_deleted boolean DEFAULT false
 );
 
 
@@ -4213,6 +4214,13 @@ CREATE INDEX index_post_versions_on_version ON public.post_versions USING btree
 CREATE INDEX index_post_votes_on_created_at ON public.post_votes USING btree (created_at);
 
 
+--
+-- Name: index_post_votes_on_is_deleted; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_post_votes_on_is_deleted ON public.post_votes USING btree (is_deleted) WHERE (is_deleted = true);
+
+
 --
 -- Name: index_post_votes_on_post_id; Type: INDEX; Schema: public; Owner: -
 --
@@ -4227,6 +4235,13 @@ CREATE INDEX index_post_votes_on_post_id ON public.post_votes USING btree (post_
 CREATE INDEX index_post_votes_on_user_id ON public.post_votes USING btree (user_id);
 
 
+--
+-- Name: index_post_votes_on_user_id_and_post_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE UNIQUE INDEX index_post_votes_on_user_id_and_post_id ON public.post_votes USING btree (user_id, post_id) WHERE (is_deleted = false);
+
+
 --
 -- Name: index_posts_on_approver_id; Type: INDEX; Schema: public; Owner: -
 --
@@ -5057,6 +5072,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20211015223510'),
 ('20211018045429'),
 ('20211018062916'),
-('20211023225730');
+('20211023225730'),
+('20211121080239');