add migration to cleanup participations

* remove author_signature column
* delete all self-participating participations
* delete all participations where author and post-author are remote
* delete all duplicate participations
* delete all participations without post
* create unique index

db/migrate/20160618033455_cleanup_participations.rb

@@ -0,0 +1,44 @@
+class CleanupParticipations < ActiveRecord::Migration
+  class Participation < ActiveRecord::Base
+  end
+
+  def up
+    remove_column :participations, :author_signature
+
+    cleanup
+
+    remove_index :participations, name: :index_participations_on_target_id_and_target_type_and_author_id
+    add_index :participations, %i(target_id target_type author_id), unique: true
+  end
+
+  def down
+    remove_index :participations, name: :index_participations_on_target_id_and_target_type_and_author_id
+    add_index :participations, %i(target_id target_type author_id)
+    add_column :participations, :author_signature, :text
+  end
+
+  private
+
+  def cleanup
+    self_where = "WHERE participations.target_type = 'Post' AND participations.target_id = posts.id AND " \
+                 "posts.author_id = participations.author_id"
+    remote_where = "WHERE participations.target_type = 'Post' AND participations.target_id = posts.id AND " \
+                   "posts.author_id = post_author.id AND participations.author_id = author.id AND " \
+                   "author.owner_id is NULL AND post_author.owner_id is NULL"
+    duplicate_where = "WHERE p1.author_id = p2.author_id AND p1.target_id = p2.target_id " \
+                      "AND p1.target_type = p2.target_type AND p1.id > p2.id"
+
+    if AppConfig.postgres?
+      execute "DELETE FROM participations USING posts #{self_where}"
+      execute "DELETE FROM participations USING posts, people AS author, people AS post_author #{remote_where}"
+      execute "DELETE FROM participations AS p1 USING participations AS p2 #{duplicate_where}"
+    else
+      execute "DELETE participations FROM participations, posts #{self_where}"
+      execute "DELETE participations FROM participations, posts, people author, people post_author #{remote_where}"
+      execute "DELETE p1 FROM participations p1, participations p2 #{duplicate_where}"
+    end
+
+    Participation.joins("LEFT OUTER JOIN posts ON posts.id = participations.target_id")
+                 .where(target_type: "Post").delete_all("posts.id is NULL")
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160531170531) do
+ActiveRecord::Schema.define(version: 20160618033455) do
 
   create_table "account_deletions", force: :cascade do |t|
     t.string   "diaspora_handle", limit: 255
@@ -312,19 +312,18 @@ ActiveRecord::Schema.define(version: 20160531170531) do
   end
 
   create_table "participations", force: :cascade do |t|
-    t.string   "guid",             limit: 255
-    t.integer  "target_id",        limit: 4
-    t.string   "target_type",      limit: 60,                null: false
-    t.integer  "author_id",        limit: 4
-    t.text     "author_signature", limit: 65535
-    t.datetime "created_at",                                 null: false
-    t.datetime "updated_at",                                 null: false
-    t.integer  "count",            limit: 4,     default: 1, null: false
+    t.string   "guid",        limit: 255
+    t.integer  "target_id",   limit: 4
+    t.string   "target_type", limit: 60,              null: false
+    t.integer  "author_id",   limit: 4
+    t.datetime "created_at",                          null: false
+    t.datetime "updated_at",                          null: false
+    t.integer  "count",       limit: 4,   default: 1, null: false
   end
 
   add_index "participations", ["author_id"], name: "index_participations_on_author_id", using: :btree
   add_index "participations", ["guid"], name: "index_participations_on_guid", length: {"guid"=>191}, using: :btree
-  add_index "participations", ["target_id", "target_type", "author_id"], name: "index_participations_on_target_id_and_target_type_and_author_id", using: :btree
+  add_index "participations", ["target_id", "target_type", "author_id"], name: "index_participations_on_target_id_and_target_type_and_author_id", unique: true, using: :btree
 
   create_table "people", force: :cascade do |t|
     t.string   "guid",                  limit: 255,                   null: false