Make PreviewCard records reuseable between statuses (#4642)

* Make PreviewCard records reuseable between statuses

**Warning!** Migration truncates preview_cards tablec

* Allow a wider thumbnail for link preview, display it in horizontal layout (#4648)

* Delete preview cards files before truncating

* Rename old table instead of truncating it

* Add mastodon:maintenance:remove_deprecated_preview_cards

* Ignore deprecated_preview_cards in schema definition

* Fix null behaviour

db/migrate/20170901141119_truncate_preview_cards.rb

@@ -0,0 +1,30 @@
+class TruncatePreviewCards < ActiveRecord::Migration[5.1]
+  def up
+    rename_table :preview_cards, :deprecated_preview_cards
+
+    create_table :preview_cards do |t|
+      t.string     :url, default: '', null: false, index: { unique: true }
+      t.string     :title, default: '', null: false
+      t.string     :description, default: '', null: false
+      t.attachment :image
+      t.integer    :type, default: 0, null: false
+      t.text       :html, default: '', null: false
+      t.string     :author_name, default: '', null: false
+      t.string     :author_url, default: '', null: false
+      t.string     :provider_name, default: '', null: false
+      t.string     :provider_url, default: '', null: false
+      t.integer    :width, default: 0, null: false
+      t.integer    :height, default: 0, null: false
+      t.timestamps
+    end
+  end
+
+  def down
+    if ActiveRecord::Base.connection.table_exists? 'deprecated_preview_cards'
+      drop_table :preview_cards
+      rename_table :deprecated_preview_cards, :preview_cards
+    else
+      raise ActiveRecord::IrreversibleMigration, 'Previous preview cards table has already been removed'
+    end
+  end
+end

db/migrate/20170901142658_create_join_table_preview_cards_statuses.rb

@@ -0,0 +1,7 @@
+class CreateJoinTablePreviewCardsStatuses < ActiveRecord::Migration[5.1]
+  def change
+    create_join_table :preview_cards, :statuses do |t|
+      t.index [:status_id, :preview_card_id]
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170829215220) do
+ActiveRecord::Schema.define(version: 20170901142658) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -224,17 +224,14 @@ ActiveRecord::Schema.define(version: 20170829215220) do
     t.index ["uid"], name: "index_oauth_applications_on_uid", unique: true
   end
 
-  create_table "preview_cards", id: :serial, force: :cascade do |t|
-    t.bigint "status_id"
+  create_table "preview_cards", force: :cascade do |t|
     t.string "url", default: "", null: false
-    t.string "title"
-    t.string "description"
+    t.string "title", default: "", null: false
+    t.string "description", default: "", null: false
     t.string "image_file_name"
     t.string "image_content_type"
     t.integer "image_file_size"
     t.datetime "image_updated_at"
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
     t.integer "type", default: 0, null: false
     t.text "html", default: "", null: false
     t.string "author_name", default: "", null: false
@@ -243,7 +240,15 @@ ActiveRecord::Schema.define(version: 20170829215220) do
     t.string "provider_url", default: "", null: false
     t.integer "width", default: 0, null: false
     t.integer "height", default: 0, null: false
-    t.index ["status_id"], name: "index_preview_cards_on_status_id", unique: true
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["url"], name: "index_preview_cards_on_url", unique: true
+  end
+
+  create_table "preview_cards_statuses", id: false, force: :cascade do |t|
+    t.bigint "preview_card_id", null: false
+    t.bigint "status_id", null: false
+    t.index ["status_id", "preview_card_id"], name: "index_preview_cards_statuses_on_status_id_and_preview_card_id"
   end
 
   create_table "reports", id: :serial, force: :cascade do |t|
@@ -432,7 +437,6 @@ ActiveRecord::Schema.define(version: 20170829215220) do
   add_foreign_key "oauth_access_tokens", "oauth_applications", column: "application_id", on_delete: :cascade
   add_foreign_key "oauth_access_tokens", "users", column: "resource_owner_id", on_delete: :cascade
   add_foreign_key "oauth_applications", "users", column: "owner_id", on_delete: :cascade
-  add_foreign_key "preview_cards", "statuses", on_delete: :cascade
   add_foreign_key "reports", "accounts", column: "action_taken_by_account_id", on_delete: :nullify
   add_foreign_key "reports", "accounts", column: "target_account_id", on_delete: :cascade
   add_foreign_key "reports", "accounts", on_delete: :cascade