See #236: added a basic string list preference

api/funkwhale_api/common/preferences.py

 from django.conf import settings
+from django import forms
+
+from dynamic_preferences import serializers
+from dynamic_preferences import types
 from dynamic_preferences.registries import global_preferences_registry
 
 
@@ -10,3 +14,38 @@ class DefaultFromSettingMixin(object):
 def get(pref):
     manager = global_preferences_registry.manager()
     return manager[pref]
+
+
+class StringListSerializer(serializers.BaseSerializer):
+    separator = ','
+    sort = True
+
+    @classmethod
+    def to_db(cls, value, **kwargs):
+        if not value:
+            return
+
+        if type(value) not in [list, tuple]:
+            raise cls.exception(
+                "Cannot serialize, value {} is not a list or a tuple".format(
+                    value))
+
+        if cls.sort:
+            value = sorted(value)
+        return cls.separator.join(value)
+
+    @classmethod
+    def to_python(cls, value, **kwargs):
+        if not value:
+            return []
+        return value.split(',')
+
+
+class StringListPreference(types.BasePreferenceType):
+    serializer = StringListSerializer
+    field_class = forms.MultipleChoiceField
+
+    def get_api_additional_data(self):
+        d = super(StringListPreference, self).get_api_additional_data()
+        d['choices'] = self.get('choices')
+        return d

api/tests/common/test_preferences.py

+import pytest
+
+from dynamic_preferences.registries import global_preferences_registry
+from funkwhale_api.common import preferences as common_preferences
+
+
+@pytest.fixture
+def string_list_pref(preferences):
+
+    @global_preferences_registry.register
+    class P(common_preferences.StringListPreference):
+        default = ['hello']
+        section = 'test'
+        name = 'string_list'
+    yield
+    del global_preferences_registry['test']['string_list']
+
+
+@pytest.mark.parametrize('input,output', [
+    (['a', 'b', 'c'], 'a,b,c'),
+    (['a', 'c', 'b'], 'a,b,c'),
+    (('a', 'c', 'b'), 'a,b,c'),
+    ([], None),
+])
+def test_string_list_serializer_to_db(input, output):
+    s = common_preferences.StringListSerializer.to_db(input) == output
+
+
+@pytest.mark.parametrize('input,output', [
+    ('a,b,c', ['a', 'b', 'c'], ),
+    (None, []),
+    ('', []),
+])
+def test_string_list_serializer_to_python(input, output):
+    s = common_preferences.StringListSerializer.to_python(input) == output
+
+
+def test_string_list_pref_default(string_list_pref, preferences):
+    assert preferences['test__string_list'] == ['hello']
+
+
+def test_string_list_pref_set(string_list_pref, preferences):
+    preferences['test__string_list'] = ['world', 'hello']
+    assert preferences['test__string_list'] == ['hello', 'world']