add missing action for mysql charm test compatibility

Author: paulomach

actions.yaml

@@ -27,3 +27,5 @@ get-session-ssl-cipher:
 get-server-certificate:
   description: Retrieve server certificate in pem format
 
+get-legacy-mysql-credentials:
+  description: Get the credentials for the legacy mysql user

src/relations/legacy_mysql.py

@@ -7,7 +7,7 @@
 
 from literals import DATABASE_NAME, LEGACY_MYSQL_RELATION
 from ops.framework import Object
-from ops.model import ActiveStatus, BlockedStatus
+from ops.model import BlockedStatus
 
 logger = logging.getLogger(__name__)
 
@@ -25,6 +25,9 @@ def __init__(self, charm):
         self.framework.observe(
             charm.on[LEGACY_MYSQL_RELATION].relation_broken, self._on_relation_broken
         )
+        self.framework.observe(
+            charm.on.get_legacy_mysql_credentials_action, self._get_legacy_mysql_credentials
+        )
 
     def _on_relation_joined(self, event):
         if not self.charm.unit.is_leader():
@@ -71,3 +74,14 @@ def _on_relation_broken(self, _):
         self.charm.app_peer_data.pop(f"{LEGACY_MYSQL_RELATION}-password", None)
         self.charm.app_peer_data.pop(f"{LEGACY_MYSQL_RELATION}-host", None)
         self.charm.app_peer_data.pop(f"{LEGACY_MYSQL_RELATION}-database", None)
+
+    def _get_legacy_mysql_credentials(self, event) -> None:
+        """Retrieve legacy mariadb credentials."""
+        event.set_results(
+            {
+                "username": self.charm.app_peer_data[f"{LEGACY_MYSQL_RELATION}-user"],
+                "password": self.charm.app_peer_data[f"{LEGACY_MYSQL_RELATION}-password"],
+                "host": self.charm.app_peer_data[f"{LEGACY_MYSQL_RELATION}-host"],
+                "database": self.charm.app_peer_data[f"{LEGACY_MYSQL_RELATION}-database"],
+            }
+        )