Merge pull request #5 from xx396/master

Performance boost for related fields and adds support for nullable ones

csvexport/actions.py

@@ -129,15 +129,6 @@ def __str__(self):
         return ''.join(self.data)
 
 
-def get_value(item, choice):
-    fields = choice.split('.')
-    for field in fields:
-        value = getattr(item, field)
-        item = value
-        if not item: break
-    return str(value or settings.CSV_EXPORT_EMPTY_VALUE)
-
-
 def csvexport(modeladmin, request, queryset):
     """
     Admin-action to export items as csv-formatted data.
@@ -208,13 +199,18 @@ def csvexport(modeladmin, request, queryset):
             header += list(fields_form.cleaned_data[node.key])
 
         csv_data = CSVData(unique_form.cleaned_data['unique'])
+        header_fields = [f.replace('.', '__') for f in header]
+        related_fields = ['__'.join(f.split('__')[:-1]) for f in header_fields if '__' in f]
+        if related_fields:
+            queryset = queryset.select_related(*related_fields)
 
         # write csv-header and -data and return csv-data as view or download
         try:
             writer = csv.writer(csv_data, **csv_format)
             writer.writerow(tuple(f for f in header))
-            for item in queryset:
-                writer.writerow(tuple(get_value(item, f) for f in header))
+            for item in queryset.values_list(*header_fields):
+                row = tuple(f if f is not None and f != '' else settings.CSV_EXPORT_EMPTY_VALUE for f in item)
+                writer.writerow(row)
         except (csv.Error, TypeError) as exc:
             messages.error(request, 'Could not write csv-file: {}'.format(exc))
         else: