Add an optional association to backends for data snapshots

I'm a bit unsure about this, but it feels like generating snapshots
remotely is useful, but if that is supported, then a remote snapshot
won't be available locally to use. Adding the option of making them
backend specific is one way of working around this.

2 files changed, 17 insertions, 2 deletions

diff --git a/db/migrate/20180601153537_add_backend_to_govuk_guix_data_snapshot.rb b/db/migrate/20180601153537_add_backend_to_govuk_guix_data_snapshot.rb
new file mode 100644
index 0000000..9f6f7cc
--- /dev/null
+++ b/db/migrate/20180601153537_add_backend_to_govuk_guix_data_snapshot.rb
@@ -0,0 +1,5 @@
+class AddBackendToGovukGuixDataSnapshot < ActiveRecord::Migration[5.1]
+  def change
+    add_reference :govuk_guix_data_snapshots, :backend, polymorphic: true
+  end
+end
diff --git a/db/structure.sql b/db/structure.sql
index 500c09d..7b5d81f 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -81,7 +81,9 @@ CREATE TABLE public.govuk_guix_data_snapshots (
     manifest json NOT NULL,
     created_at timestamp without time zone NOT NULL,
     updated_at timestamp without time zone NOT NULL,
-    govuk_guix_revision_commit_hash character varying NOT NULL
+    govuk_guix_revision_commit_hash character varying NOT NULL,
+    backend_type character varying,
+    backend_id bigint
 );
 
 
@@ -538,6 +540,13 @@ ALTER TABLE ONLY public.users
 
 
 --
+-- Name: index_govuk_guix_data_snapshots_on_backend_type_and_backend_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_govuk_guix_data_snapshots_on_backend_type_and_backend_id ON public.govuk_guix_data_snapshots USING btree (backend_type, backend_id);
+
+
+--
 -- Name: index_govuk_guix_data_snapshots_on_store_path; Type: INDEX; Schema: public; Owner: -
 --
 
@@ -633,6 +642,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20180523062426'),
 ('20180527183740'),
 ('20180530191341'),
-('20180530192706');
+('20180530192706'),
+('20180601153537');