perf: cache live access data during request (#46854)

tests/test_formdata.py

@@ -7,6 +7,7 @@ import sys
 import shutil
 import time
 
+import mock
 from django.utils import six
 from quixote import cleanup
 from quixote.http_request import Upload
@@ -827,11 +828,19 @@ def test_lazy_formdata_live_item(pub):
     assert context['form_var_foo_live_var_attr'] == 'attr2'
     assert 'form_var_foo_live_var_attr' in context.get_flat_keys()
 
-    CardDef.wipe()
+    pub.get_request().live_card_cache = {}
     context = pub.substitutions.get_context_variables(mode='lazy')
-    with pytest.raises(KeyError):
-        context['form_var_foo_live_name']
-    assert 'form_var_foo_live_var_attr' not in context.get_flat_keys()
+    # mock missing carddef to get call count
+    with mock.patch('wcs.carddef.CardDef.get_by_urlname') as get_by_urlname:
+        get_by_urlname.side_effect = KeyError
+
+        with pytest.raises(KeyError):
+            context['form_var_foo_live_name']
+        assert get_by_urlname.call_count == 1
+        with pytest.raises(KeyError):  # repeated access, will go through cache
+            context['form_var_foo_live_name']
+        assert get_by_urlname.call_count == 1
+        assert 'form_var_foo_live_var_attr' not in context.get_flat_keys()
 
 
 def test_lazy_formdata_queryset(pub, variable_test_data):

wcs/variables.py

@@ -687,11 +687,28 @@ class LazyFieldVarStructured(LazyFieldVar):
     def live(self):
         if not (self._field.data_source and self._field.data_source.get('type', '').startswith('carddef:')):
             raise AttributeError('live')
+        request = get_request()
+        if request:
+            # cache during request
+            cache_key = '%s-%s' % (self._field.data_source['type'], self.raw)
+            if not hasattr(request, 'live_card_cache'):
+                request.live_card_cache = {}
+            else:
+                carddata = request.live_card_cache.get(cache_key)
+                if carddata is not None:
+                    # cached data
+                    if isinstance(carddata, Exception):
+                        raise carddata
+                    return LazyFormData(carddata)
         from wcs.carddef import CardDef
         try:
             carddef = CardDef.get_by_urlname(self._field.data_source['type'][8:])
             carddata = carddef.data_class().get(self.raw)
+            if request:
+                request.live_card_cache[cache_key] = carddata
         except KeyError:
+            if request:
+                request.live_card_cache[cache_key] = AttributeError('live')
             raise AttributeError('live')
         return LazyFormData(carddata)