Merge ~pjdc/interface-pgsql/+git/operator:fixes into ~stub/interface-pgsql/+git/operator:master

[Paul Collins]

code fixes: EventSetBase was renamed to ObjectEvents, return value of _standbys needs to be marashallable for StoredStateData; doc fixes: it's DatabaseRelationJoinedEvent, not DatabaseJoinedEvent, db relation count check off-by-one

diff --git a/README.md b/README.md
index 9e74611..72d8939 100644
--- a/README.md
+++ b/README.md
@@ -26,11 +26,11 @@ class MyCharm(ops.charm.CharmBase):
         super().__init__(*args)
         self.state.set_default(db_conn_str=None, db_uri=None, db_ro_uris=[])
         self.db = pgsql.PostgreSQLClient(self, 'db')  # 'db' relation required in metadata.yaml
-        self.framework.observe(self.db.on.database_joined, self.on_database_joined)
+        self.framework.observe(self.db.on.database_joined, self.on_database_relation_joined)
         self.framework.observe(self.db.on.master_changed, self.on_master_changed)
         self.framework.observe(self.db.on.standby_changed, self.on_standby_changed)
 
-    def on_database_joined(self, event: pgsql.DatabaseJoinedEvent):
+    def on_database_joined(self, event: pgsql.DatabaseRelationJoinedEvent):
         if self.model.unit.is_leader():
             # Provide requirements to the PostgreSQL server.
             event.database = 'mydbname'  # Request database named mydbname
@@ -45,7 +45,7 @@ class MyCharm(ops.charm.CharmBase):
         # Enforce a single 'db' relation, or else we risk directing writes to
         # an the wrong backend. This can happen via user error, or redeploying
         # the PostgreSQL backend.
-        if len(self.model.relations['db']) > 0:
+        if len(self.model.relations['db']) > 1:
             self.unit.status = ops.model.BlockedStatus("Too many db relations!")
             event.defer()
             return
@@ -71,7 +71,7 @@ class MyCharm(ops.charm.CharmBase):
         # are available.
 
     def on_standby_changed(self, event: pgsql.StandbyChangedEvent):
-         if len(self.model.relations['db']) > 0:
+         if len(self.model.relations['db']) > 1:
             self.unit.status = ops.model.BlockedStatus("Too many db relations!")
             event.defer()
             return
diff --git a/pgsql/pgsql.py b/pgsql/pgsql.py
index 83d4444..82835cf 100644
--- a/pgsql/pgsql.py
+++ b/pgsql/pgsql.py
@@ -285,7 +285,7 @@ class StandbyGoneEvent(PostgreSQLRelationEvent):
     pass
 
 
-class PostgreSQLClientEvents(ops.framework.EventSetBase):
+class PostgreSQLClientEvents(ops.framework.ObjectEvents):
     database_relation_joined = ops.framework.EventSource(DatabaseRelationJoinedEvent)
     database_relation_broken = ops.framework.EventSource(DatabaseRelationBrokenEvent)
     database_available = ops.framework.EventSource(DatabaseAvailableEvent)
@@ -578,7 +578,7 @@ def _standbys(log: logging.Logger, relation: ops.model.Relation, local_unit: ops
         if raw:
             if _is_ready(log, appdata, locdata, reldata):
                 log.debug('ready standbys found on relation %s', relation.id)
-                return (conn_str for conn_str in raw.splitlines() if conn_str)
+                return [conn_str for conn_str in raw.splitlines() if conn_str]
             log.debug('unready standbys found on relation %s', relation.id)
     log.debug('no ready standbys found on relation %s', relation.id)
     return []