Implement DEPRECATED mysql-shared interface

metadata.yaml

@@ -13,13 +13,13 @@ summary: |
   Enables effective access to a MySQL cluster with Group Replication.
 subordinate: true
 provides:
-# TODO: re-implement legacy relation
-#  shared-db:
-#    interface: mysql-shared
-#    scope: container
   database:
     interface: mysql_client
     scope: container
+  # DEPRECATED shared-db: Legacy "mysql-shared" interface
+  deprecated-shared-db:
+    interface: mysql-shared
+    scope: container
 requires:
   backend-database:
     interface: mysql_client
@@ -29,7 +29,10 @@ requires:
   juju-info:
     interface: juju-info
     scope: container
+peers:
 # TODO TLS VM: re-enable peer relation
-#peers:
 #  mysql-router-peers:
 #    interface: mysql_router_peers
+  # DEPRECATED shared-db: Workaround for legacy "mysql-shared" interface using unit databags instead of app databag
+  deprecated-shared-db-credentials:
+    interface: _deprecated_shared_db_peers

src/machine_charm.py

@@ -11,6 +11,7 @@
 import ops
 
 import abstract_charm
+import relations.database_providers_wrapper
 import snap
 import socket_workload
 
@@ -23,6 +24,10 @@ class MachineSubordinateRouterCharm(abstract_charm.MySQLRouterCharm):
 
     def __init__(self, *args) -> None:
         super().__init__(*args)
+        # DEPRECATED shared-db: Enable legacy "mysql-shared" interface
+        del self._database_provides
+        self._database_provides = relations.database_providers_wrapper.RelationEndpoint(self)
+
         self._authenticated_workload_type = socket_workload.AuthenticatedSocketWorkload
         self.framework.observe(self.on.install, self._on_install)
         self.framework.observe(self.on.remove, self._on_remove)

src/relations/database_providers_wrapper.py

@@ -0,0 +1,82 @@
+# Copyright 2023 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""Relation(s) to one or more application charms
+
+Wraps modern interface (database_provides.py) and DEPRECATED legacy interface
+(deprecated_shared_db_database_provides.py)
+"""
+
+import typing
+
+import ops
+
+import mysql_shell
+import relations.database_provides
+
+# `as` used to fix type checking circular import
+import relations.deprecated_shared_db_database_provides as deprecated_shared_db_database_provides
+
+if typing.TYPE_CHECKING:
+    import abstract_charm
+
+
+class RelationEndpoint:
+    """Relation endpoints for application charm(s)
+
+    Wraps modern interface (database_provides.py) endpoint and DEPRECATED legacy interface
+    (deprecated_shared_db_database_provides.py) endpoint
+    """
+
+    def __init__(self, charm_: "abstract_charm.MySQLRouterCharm") -> None:
+        self._database_provides = relations.database_provides.RelationEndpoint(charm_)
+        self._deprecated_shared_db = deprecated_shared_db_database_provides.RelationEndpoint(
+            charm_
+        )
+
+    def reconcile_users(
+        self,
+        *,
+        event,
+        router_read_write_endpoint: str,
+        router_read_only_endpoint: str,
+        shell: mysql_shell.Shell,
+    ) -> None:
+        """Create requested users and delete inactive users.
+
+        When the relation to the MySQL charm is broken, the MySQL charm will delete all users
+        created by this charm. Therefore, this charm does not need to delete users when that
+        relation is broken.
+        """
+        self._database_provides.reconcile_users(
+            event=event,
+            router_read_write_endpoint=router_read_write_endpoint,
+            router_read_only_endpoint=router_read_only_endpoint,
+            shell=shell,
+        )
+        self._deprecated_shared_db.reconcile_users(event=event, shell=shell)
+
+    def delete_all_databags(self) -> None:
+        """Remove connection information from all databags.
+
+        Called when relation with MySQL is breaking
+
+        When the MySQL relation is re-established, it could be a different MySQL cluster—new users
+        will need to be created.
+        """
+        self._database_provides.delete_all_databags()
+        self._deprecated_shared_db.delete_all_databags()
+
+    def get_status(self, event) -> typing.Optional[ops.StatusBase]:
+        """Report non-active status."""
+        database_provides_status = self._database_provides.get_status(event)
+        deprecated_shared_db_status = self._deprecated_shared_db.get_status(event)
+        if (
+            isinstance(deprecated_shared_db_status, ops.ActiveStatus)
+            and isinstance(database_provides_status, ops.BlockedStatus)
+            and database_provides_status.message.startswith("Missing relation:")
+        ):
+            return deprecated_shared_db_status
+        if database_provides_status:
+            return database_provides_status
+        return deprecated_shared_db_status