Add validation for unique name when creating new Setting

tailbone/views/settings.py

@@ -30,9 +30,18 @@ import re
 
 from rattail.db import model
 
+import formalchemy as fa
+
+from tailbone.db import Session
 from tailbone.views import MasterView
 
 
+def unique_name(value, field):
+    setting = Session.query(model.Setting).get(value)
+    if setting:
+        raise fa.ValidationError("Setting name must be unique")
+
+
 class SettingsView(MasterView):
     """
     Master view for the settings model.
@@ -51,15 +60,17 @@ class SettingsView(MasterView):
             ],
             readonly=True)
 
-    def configure_fieldset(self, fs):
-        fs.configure(
-            include=[
-                fs.name,
-                fs.value,
-            ])
+    def _preconfigure_fieldset(self, fs):
+        fs.name.set(validate=unique_name)
         if self.editing:
             fs.name.set(readonly=True)
 
+    def configure_fieldset(self, fs):
+        fs.configure(include=[
+            fs.name,
+            fs.value,
+        ])
+
     def editable_instance(self, setting):
         if self.rattail_config.demo():
             return not bool(self.feedback.match(setting.name))