migrations: add cascading deletes for tables interleaved under versions

This CL adds ON DELETE CASCADE to foreign keys
referencing the versions table, so that deleting a version also deletes
all corresponding data.

Updates b/132710180
Updates b/131789052

Change-Id: I793d2b8b1769cda8b667d3d32c28728e79ac4b4a
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/466436
Reviewed-by: Andrew Bonventre <andybons@google.com>

migrations/000044_add_cascading_deletes.down.sql

@@ -0,0 +1,42 @@
+-- Copyright 2019 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+
+BEGIN;
+
+ALTER TABLE licenses
+  DROP CONSTRAINT "licenses_module_path_fkey",
+  ADD CONSTRAINT "licenses_module_path_fkey"
+    FOREIGN KEY (module_path, version)
+    REFERENCES versions(module_path, version);
+
+ALTER TABLE packages
+  DROP CONSTRAINT "packages_module_path_fkey",
+  ADD CONSTRAINT "packages_module_path_fkey"
+    FOREIGN KEY (module_path, version)
+    REFERENCES versions(module_path, version);
+
+ALTER TABLE package_licenses
+  DROP CONSTRAINT "package_licenses_module_path_fkey",
+  ADD CONSTRAINT "package_licenses_module_path_fkey"
+    FOREIGN KEY (module_path, version, package_path)
+    REFERENCES packages(module_path, version, path),
+  DROP CONSTRAINT "package_licenses_module_path_fkey1",
+  ADD CONSTRAINT "package_licenses_module_path_fkey1"
+    FOREIGN KEY (module_path, version, file_path)
+    REFERENCES licenses(module_path, version, file_path);
+
+ALTER TABLE documents
+  DROP CONSTRAINT "documents_package_path_fkey",
+  ADD CONSTRAINT "documents_package_path_fkey"
+    FOREIGN KEY (package_path, module_path, version)
+    REFERENCES packages(path, module_path, version);
+
+ALTER TABLE imports
+  DROP CONSTRAINT "imports_from_path_fkey",
+  ADD CONSTRAINT "imports_from_path_fkey"
+    FOREIGN KEY (from_path, from_module_path, from_version)
+    REFERENCES packages(path, module_path, version);
+
+END;

migrations/000044_add_cascading_deletes.up.sql

@@ -0,0 +1,47 @@
+-- Copyright 2019 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE licenses
+  DROP CONSTRAINT "licenses_module_path_fkey",
+  ADD CONSTRAINT "licenses_module_path_fkey"
+    FOREIGN KEY (module_path, version)
+    REFERENCES versions(module_path, version)
+    ON DELETE CASCADE;
+
+ALTER TABLE packages
+  DROP CONSTRAINT "packages_module_path_fkey",
+  ADD CONSTRAINT "packages_module_path_fkey"
+    FOREIGN KEY (module_path, version)
+    REFERENCES versions(module_path, version)
+    ON DELETE CASCADE;
+
+ALTER TABLE package_licenses
+  DROP CONSTRAINT "package_licenses_module_path_fkey",
+  ADD CONSTRAINT "package_licenses_module_path_fkey"
+    FOREIGN KEY (module_path, version, package_path)
+    REFERENCES packages(module_path, version, path)
+    ON DELETE CASCADE,
+  DROP CONSTRAINT "package_licenses_module_path_fkey1",
+  ADD CONSTRAINT "package_licenses_module_path_fkey1"
+    FOREIGN KEY (module_path, version, file_path)
+    REFERENCES licenses(module_path, version, file_path)
+    ON DELETE CASCADE;
+
+ALTER TABLE documents
+  DROP CONSTRAINT "documents_package_path_fkey",
+  ADD CONSTRAINT "documents_package_path_fkey"
+    FOREIGN KEY (package_path, module_path, version)
+    REFERENCES packages(path, module_path, version)
+    ON DELETE CASCADE;
+
+ALTER TABLE imports
+  DROP CONSTRAINT "imports_from_path_fkey",
+  ADD CONSTRAINT "imports_from_path_fkey"
+    FOREIGN KEY (from_path, from_module_path, from_version)
+    REFERENCES packages(path, module_path, version)
+    ON DELETE CASCADE;
+
+END;