asset: Feld 'change_symbol' für Prozenzzeichen + test

asset.py

@@ -114,6 +114,9 @@ class Asset(SymbolMixin, ModelSQL, ModelView):
         help='percentage change in value during 1 year',
         readonly=True, digits=(16,digits_percent)),
         'get_percentage_change', searcher='search_percentage')
+    change_symbol = fields.Function(fields.Many2One(string='Symbol',
+        readonly=True, model_name='investment.rate'),
+        'get_percentage_change')
 
     @classmethod
     def __register__(cls, module_name):
@@ -564,10 +567,12 @@ class Asset(SymbolMixin, ModelSQL, ModelView):
         """
         cursor = Transaction().connection.cursor()
 
-        name_lst = [x[len('change_'):] for x in names]
+        name_lst = [x[len('change_'):] for x in names
+            if x != 'change_symbol']
         tab_percent = cls.get_percentage_sql(name_lst)
         query = tab_percent.select(
                 tab_percent.id,
+                tab_percent.id_rate,
                 *[getattr(tab_percent, x) for x in name_lst],
                 where=tab_percent.id.in_([x.id for x in assets]),
             )
@@ -577,7 +582,10 @@ class Asset(SymbolMixin, ModelSQL, ModelView):
         result = {x:{y.id: None for y in assets} for x in names}
         exp = Decimal(Decimal(1) / 10 ** digits_percent)
         for record in records:
-            cnt1 = 1
+            if 'change_symbol' in names:
+                result['change_symbol'][record[0]] = record[1]
+
+            cnt1 = 2
             for x in name_lst:
                 result['change_%s' % x][record[0]] = record[cnt1].quantize(exp) \
                     if record[cnt1] is not None else None