attributes migration

Add a new table that allows for attributes in json form #505

db/migrate/20181129000515_create_attributes_table.rb

@@ -0,0 +1,27 @@
+class CreateAttributesTable < ActiveRecord::Migration[5.1]
+  def change
+    this_hostid = Machine.new.hostid
+
+    create_table :attributes, id: :bigint do |t|
+      t.string :container_type, null: false
+      t.integer :container_id, limit: 8, null: false
+      t.jsonb :value, null: false, default: '{}'
+      t.timestamps
+    end
+
+    add_index :attributes, :container_id
+    add_index :attributes, :value, using: :gin
+
+    reversible do |dir|
+      dir.up do
+        execute %{
+          SELECT setval('attributes_id_seq', GREATEST(1, 1 + CAST(1e9 * #{this_hostid}::int AS bigint)), FALSE);
+          ALTER TABLE "attributes"
+            ALTER COLUMN created_at SET DEFAULT utc_now(),
+            ALTER COLUMN updated_at SET DEFAULT utc_now(),
+            ADD CONSTRAINT container_type_id UNIQUE(container_type, container_id);
+        }
+      end
+    end  
+  end
+end