Fix delete user call when user was not created before (#75)

* Fix delete user call when user was not created before

* Add integration test for the fix

lib/charms/postgresql_k8s/v0/postgresql.py

@@ -32,7 +32,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 6
+LIBPATCH = 7
 
 
 logger = logging.getLogger(__name__)
@@ -184,6 +184,11 @@ def delete_user(self, user: str) -> None:
         Args:
             user: user to be deleted.
         """
+        # First of all, check whether the user exists. Otherwise, do nothing.
+        users = self.list_users()
+        if user not in users:
+            return
+
         # List all databases.
         try:
             with self._connect_to_database() as connection, connection.cursor() as cursor:

tests/integration/new_relations/application-charm/metadata.yaml

@@ -17,3 +17,5 @@ requires:
   aliased-multiple-database-clusters:
     interface: postgresql_client
     limit: 2
+  no-database:
+    interface: postgresql_client

tests/integration/new_relations/application-charm/src/charm.py

@@ -103,6 +103,9 @@ def __init__(self, *args):
             self._on_cluster2_endpoints_changed,
         )
 
+        # Relation used to test the situation where no database name is provided.
+        self.no_database = DatabaseRequires(self, "no-database", database_name="")
+
     def _on_start(self, _) -> None:
         """Only sets an Active status."""
         self.unit.status = ActiveStatus()

tests/integration/new_relations/test_new_relations.py

@@ -28,6 +28,7 @@
 SECOND_DATABASE_RELATION_NAME = "second-database"
 MULTIPLE_DATABASE_CLUSTERS_RELATION_NAME = "multiple-database-clusters"
 ALIASED_MULTIPLE_DATABASE_CLUSTERS_RELATION_NAME = "aliased-multiple-database-clusters"
+NO_DATABASE_RELATION_NAME = "no-database"
 
 
 @pytest.mark.abort_on_fail
@@ -358,3 +359,20 @@ async def test_restablish_relation(ops_test: OpsTest):
         cursor.execute("SELECT data FROM test;")
         data = cursor.fetchone()
         assert data[0] == "other data"
+
+
+@pytest.mark.database_relation_tests
+async def test_relation_with_no_database_name(ops_test: OpsTest):
+    """Test that a relation with no database name doesn't block the charm."""
+    async with ops_test.fast_forward():
+        # Relate the charms using a relation that doesn't provide a database name.
+        await ops_test.model.add_relation(
+            f"{APPLICATION_APP_NAME}:{NO_DATABASE_RELATION_NAME}", DATABASE_APP_NAME
+        )
+        await ops_test.model.wait_for_idle(apps=APP_NAMES, status="active", raise_on_blocked=True)
+
+        # Break the relation.
+        await ops_test.model.applications[DATABASE_APP_NAME].remove_relation(
+            f"{DATABASE_APP_NAME}", f"{APPLICATION_APP_NAME}:{NO_DATABASE_RELATION_NAME}"
+        )
+        await ops_test.model.wait_for_idle(apps=APP_NAMES, status="active", raise_on_blocked=True)