Merge ~twom/launchpad:ocirecipe-git-path-allow-null into launchpad:db-devel

[Tom Wardill]

Allow OCIRecipe.git_path to be null and add constraints

We want to be able to 'detach' the OCIRecipe from it's repository (for instance, allowing the repo to be deleted, but maintaining the history and configuration of the recipe).
Allow git_path to be NULL, the same as git_repository, and add a constraint that if one is NULL, the other should be too.

Matches the behaviour of Snap*

[Colin Watson (cjwatson)]

review: Approve (db)

diff --git a/database/schema/patch-2210-08-4.sql b/database/schema/patch-2210-08-4.sql
new file mode 100644
index 0000000..4656bb7
--- /dev/null
+++ b/database/schema/patch-2210-08-4.sql
@@ -0,0 +1,8 @@
+-- Copyright 2020 Canonical Ltd.  This software is licensed under the
+-- GNU Affero General Public License version 3 (see the file LICENSE).
+
+ALTER TABLE OCIRecipe ALTER COLUMN git_path DROP NOT NULL;
+
+ALTER TABLE OCIRecipe ADD CONSTRAINT consistent_git_ref CHECK ((git_repository IS NULL) = (git_path IS NULL));
+
+INSERT INTO LaunchpadDatabaseRevision VALUES (2210, 08, 4);