models: Fix encoding error in Identifier field

Fixes #1508

docs/changelog.rst

@@ -46,6 +46,10 @@ Bug fix release.
   one. Particularly relevant for Mopidy-Scrobbler users, as before it was
   essentially unusable. (Fixes: :issue:`1456`, PR: :issue:`1534`)
 
+- Models: Fix encoding error if :class:`~mopidy.models.fields.Identifier`
+  fields, like the ``musicbrainz_id`` model fields, contained non-ASCII Unicode
+  data. (Fixes: :issue:`1508`, PR: :issue:`1546`)
+
 - File: Ensure path comparision is done between bytestrings only. Fixes crash
   where a :confval:`file/media_dirs` path contained non-ASCII characters.
   (Fixes: :issue:`1345`, PR: :issue:`1493`)

mopidy/models/fields.py

@@ -88,14 +88,17 @@ class Date(String):
 
 class Identifier(String):
     """
-    :class:`Field` for storing ASCII values such as GUIDs or other identifiers.
+    :class:`Field` for storing values such as GUIDs or other identifiers.
 
     Values will be interned.
 
     :param default: default value for field
     """
     def validate(self, value):
-        return compat.intern(str(super(Identifier, self).validate(value)))
+        value = super(Identifier, self).validate(value)
+        if isinstance(value, compat.text_type):
+            value = value.encode('utf-8')
+        return compat.intern(value)
 
 
 class URI(Identifier):

tests/models/test_fields.py

@@ -1,3 +1,5 @@
+# encoding: utf-8
+
 from __future__ import absolute_import, unicode_literals
 
 import unittest
@@ -146,6 +148,11 @@ class IdentifierTest(unittest.TestCase):
         instance.attr = u'abc'
         self.assertEqual(u'abc', instance.attr)
 
+    def test_unicode_with_nonascii_allowed(self):
+        instance = create_instance(Identifier())
+        instance.attr = u'æøå'
+        self.assertEqual(u'æøå'.encode('utf-8'), instance.attr)
+
     def test_other_disallowed(self):
         instance = create_instance(Identifier())
         with self.assertRaises(TypeError):