Update conversation lastMessage from database

Don't set lastMessage, let it update itself as needed, such as when
first rendering a conversation list item, and when its messages are
sent, received, or destroyed.

js/models/conversations.js

@@ -59,7 +59,6 @@
             received_at    : timestamp,
             key_changed    : id
         });
-        this.set({ lastMessage: message.getNotificationText() });
         message.save().then(this.trigger.bind(this,'newmessage', message));
     },
 
@@ -185,15 +184,18 @@
     },
 
     updateLastMessage: function() {
-        var lastMessage = this.messageCollection.at(this.messageCollection.length - 1);
-        if (lastMessage) {
-          this.save({
-            lastMessage : lastMessage.getNotificationText(),
-            timestamp   : lastMessage.get('sent_at')
-          });
-        } else {
-          this.save({ lastMessage: '', timestamp: null });
-        }
+        var collection = new Whisper.MessageCollection();
+        return collection.fetchConversation(this.id, 1).then(function() {
+            var lastMessage = collection.at(0);
+            if (lastMessage) {
+              this.save({
+                lastMessage : lastMessage.getNotificationText(),
+                timestamp   : lastMessage.get('sent_at')
+              });
+            } else {
+              this.save({ lastMessage: '', timestamp: null });
+            }
+        }.bind(this));
     },
 
     updateExpirationTimer: function(expireTimer, source, received_at) {

js/models/messages.js

@@ -424,10 +424,6 @@
                                 timestamp: message.get('sent_at')
                             });
                         }
-                        conversation.set({
-                            lastMessage: message.getNotificationText()
-                        });
-
                         message.save().then(function() {
                             conversation.save().then(function() {
                                 conversation.trigger('newmessage', message);

js/views/conversation_list_item_view.js

@@ -22,8 +22,11 @@
             this.listenTo(this.model, 'opened', this.markSelected); // auto update
             this.listenTo(this.model.messageCollection, 'add remove',
               _.debounce(this.model.updateLastMessage.bind(this.model), 1000));
+            this.listenTo(this.model, 'newmessage',
+              _.debounce(this.model.updateLastMessage.bind(this.model), 1000));
             extension.windows.onClosed(this.stopListening.bind(this));
             this.timeStampView = new Whisper.TimestampView({brief: true});
+            this.model.updateLastMessage();
         },
 
         markSelected: function() {