Skip database creation for mysqlrouter extra user role (#210)

Ported from canonical/mysql-k8s-operator#227

lib/charms/mysql/v0/mysql.py

@@ -91,7 +91,7 @@ def wait_until_mysql_connection(self) -> None:
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 27
+LIBPATCH = 28
 
 UNIT_TEARDOWN_LOCKNAME = "unit-teardown"
 
@@ -487,6 +487,7 @@ def create_application_database_and_scoped_user(
         hostname: str,
         *,
         unit_name: str = None,
+        create_database: bool = True,
     ) -> None:
         """Create an application database and a user scoped to the created database.
 
@@ -496,6 +497,7 @@ def create_application_database_and_scoped_user(
             password: The password of the scoped user
             hostname: The hostname of the scoped user
             unit_name: The name of the unit from which the user will be accessed
+            create_database: Whether to create database
 
         Raises MySQLCreateApplicationDatabaseAndScopedUserError
             if there is an issue creating the application database or a user scoped to the database
@@ -521,7 +523,8 @@ def create_application_database_and_scoped_user(
                 f'session.run_sql("GRANT ALL PRIVILEGES ON `{database_name}`.* TO `{username}`@`{hostname}`;")',
             )
 
-            self._run_mysqlsh_script("\n".join(create_database_commands))
+            if create_database:
+                self._run_mysqlsh_script("\n".join(create_database_commands))
             self._run_mysqlsh_script("\n".join(create_scoped_user_commands))
         except MySQLClientError as e:
             logger.exception(

src/relations/mysql_provider.py

@@ -218,16 +218,25 @@ def _on_database_requested(self, event: DatabaseRequestedEvent):
             self.database.set_endpoints(relation_id, rw_endpoints)
             self.database.set_version(relation_id, db_version)
             self.database.set_read_only_endpoints(relation_id, ro_endpoints)
-            # TODO:
-            # add setup of tls, tls_ca and status
-            self.charm._mysql.create_application_database_and_scoped_user(
-                db_name, db_user, db_pass, "%"
-            )
 
             if "mysqlrouter" in extra_user_roles:
+                self.charm._mysql.create_application_database_and_scoped_user(
+                    db_name,
+                    db_user,
+                    db_pass,
+                    "%",
+                    # MySQL Router charm does not need a new database
+                    create_database=False,
+                )
                 self.charm._mysql.grant_privileges_to_user(
                     db_user, "%", ["ALL PRIVILEGES"], with_grant_option=True
                 )
+            else:
+                # TODO:
+                # add setup of tls, tls_ca and status
+                self.charm._mysql.create_application_database_and_scoped_user(
+                    db_name, db_user, db_pass, "%"
+                )
 
             logger.info(f"Created user for app {remote_app}")
         except (