Check workload version

Author: carlcsaposs-canonical

src/abstract_charm.py

@@ -41,15 +41,26 @@ def is_compatible(
         old_workload_version: str,
         new_workload_version: str,
     ) -> bool:
+        # Check charm version compatibility
         if not super().is_compatible(
             old_charm_version=old_charm_version,
             new_charm_version=new_charm_version,
             old_workload_version=old_workload_version,
             new_workload_version=new_workload_version,
         ):
             return False
-        # TODO: check workload version—prevent downgrade?
-        return True
+
+        # Check workload version compatibility
+        old_major, old_minor, old_patch = (int(component) for component in old_workload_version.split("."))
+        new_major, new_minor, new_patch = (int(component) for component in new_workload_version.split("."))
+        if old_major != new_major:
+            return False
+        if new_minor > old_minor:
+            return True
+        elif new_minor == old_minor:
+            return new_patch >= old_patch
+        else:
+            return False
 
 
 class MySQLRouterCharm(ops.CharmBase, abc.ABC):