From e190768d7ae3db400e744d6d1d594969aacd2bf9 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 31 Jul 2018 13:31:10 -0400
Subject: [PATCH 1/3] Disallow duplicate component ids.

---
 dash/dash.py       | 25 ++++++++++++++++++-------
 dash/exceptions.py |  4 ++++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 32d6ee1b22..84bad37263 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -843,13 +843,8 @@ def dispatch(self):
 
         return self.callback_map[target_id]['callback'](*args)
 
-    def _setup_server(self):
-        if self.config.include_assets_files:
-            self._walk_assets_directory()
-
-        # Make sure `layout` is set before running the server
-        value = getattr(self, 'layout')
-        if value is None:
+    def _validate_layout(self):
+        if self.layout is None:
             raise exceptions.NoLayoutException(
                 ''
                 'The layout was `None` '
@@ -857,6 +852,22 @@ def _setup_server(self):
                 'Make sure to set the `layout` attribute of your application '
                 'before running the server.')
 
+        layout_id = getattr(self.layout, 'id', None)
+
+        component_ids = {layout_id} if layout_id else set()
+        for component in self.layout.traverse():
+            component_id = getattr(component, 'id', None)
+            if component_id and component_id in component_ids:
+                raise exceptions.DuplicateIdError(
+                    'Duplicate component id found : `{}`'.format(component_id))
+            component_ids.add(component_id)
+
+    def _setup_server(self):
+        if self.config.include_assets_files:
+            self._walk_assets_directory()
+
+        self._validate_layout()
+
         self._generate_scripts_html()
         self._generate_css_dist_html()
 
diff --git a/dash/exceptions.py b/dash/exceptions.py
index c459b0e5c2..58cf322715 100644
--- a/dash/exceptions.py
+++ b/dash/exceptions.py
@@ -50,5 +50,9 @@ class PreventUpdate(CallbackException):
     pass
 
 
+class DuplicateIdError(DashException):
+    pass
+
+
 class InvalidCallbackReturnValue(CallbackException):
     pass

From f591ae59b4e5a31552ba2b83a199cb6f1e544668 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Thu, 9 Aug 2018 15:00:25 -0400
Subject: [PATCH 2/3] Specify duplicate component id in initial layout.

---
 dash/dash.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/dash/dash.py b/dash/dash.py
index 84bad37263..d5142e0a03 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -859,7 +859,8 @@ def _validate_layout(self):
             component_id = getattr(component, 'id', None)
             if component_id and component_id in component_ids:
                 raise exceptions.DuplicateIdError(
-                    'Duplicate component id found : `{}`'.format(component_id))
+                    'Duplicate component id found'
+                    ' in the initial layout: `{}`'.format(component_id))
             component_ids.add(component_id)
 
     def _setup_server(self):

From 2d8a0334089904e172d6b735c4017c47d85ae40e Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Mon, 13 Aug 2018 12:41:53 -0400
Subject: [PATCH 3/3] Update version and CHANGELOG.md

---
 CHANGELOG.md    | 3 +++
 dash/version.py | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e8a66948e2..18cb569800 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 0.24.2 - 2018-08-13
+## Fixed
+- Disallow duplicate component ids in the initial layout. [#320](https://github.com/plotly/dash/pull/320)
 
 ## 0.24.1 - 2018-08-10
 ## Fixed
diff --git a/dash/version.py b/dash/version.py
index 7fe14931d2..d1d123f305 100644
--- a/dash/version.py
+++ b/dash/version.py
@@ -1 +1 @@
-__version__ = '0.24.1'
+__version__ = '0.24.2'