feat(migrate): add migration script to delete orphan templates

This script identifies and removes templates without associated dataverses, addressing issue IQSS#8600. It also updates dataverses using such templates as defaults before deleting the orphan templates to ensure data integrity.

Author: poikilotherm

modules/dataverse-migrate-db/extra-migrations/V5.10.0.0__8600-orphaned-templates.sql

@@ -0,0 +1,49 @@
+-- Migration script to delete orphan templates (templates with no associated dataverse), see also issue #8600
+
+DO
+$$
+    DECLARE
+        orphan_templates_count INTEGER;
+        affected_collections_count INTEGER;
+        row_count INTEGER;
+    BEGIN
+        -- Get the count of orphan templates
+        SELECT COUNT(t.id) INTO orphan_templates_count
+        FROM template t
+        WHERE dataverse_id IS NULL;
+
+        -- Count dataverse collections that use orphan templates as default
+        SELECT COUNT(*) INTO affected_collections_count
+        FROM dataverse d
+        WHERE d.defaulttemplate_id IN (
+            SELECT t.id FROM template t WHERE dataverse_id IS NULL
+        );
+
+        -- Only show hint if count is greater than 0
+        IF orphan_templates_count > 0 THEN
+            RAISE NOTICE '--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---';
+            RAISE NOTICE 'Found % orphan templates (templates with no associated dataverse)', orphan_templates_count;
+            RAISE NOTICE 'Found % dataverses using orphan templates as their default template', affected_collections_count;
+
+            -- First, update all dataverses that use orphan templates as default template
+            UPDATE dataverse
+            SET defaulttemplate_id = NULL
+            WHERE defaulttemplate_id IN (
+                SELECT t.id FROM template t WHERE dataverse_id IS NULL
+            );
+
+            GET DIAGNOSTICS row_count = ROW_COUNT;
+            RAISE NOTICE 'Updated % collections to remove references to orphan templates', row_count;
+
+            -- Then delete all orphan templates
+            DELETE FROM template
+            WHERE dataverse_id IS NULL;
+
+            GET DIAGNOSTICS row_count = ROW_COUNT;
+            RAISE NOTICE 'Deleted % orphan templates', row_count;
+
+            COMMIT;
+            RAISE NOTICE '--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---';
+        END IF;
+    END
+$$;