Repeat calls to SolrQuerySet.only should replace, not extend field limit

CHANGELOG.rst

@@ -3,6 +3,13 @@
 CHANGELOG
 =========
 
+
+0.2
+---
+
+* Subquent calls to SolrQuerySet.only() now *replaces* field limit options
+  rather than adding to them.
+
 0.1.1
 -----
 

parasolr/query.py

@@ -193,14 +193,16 @@ def query(self, **kwargs):
 
     def only(self, *args, **kwargs):
         """Use field limit option to return only the specified fields.
-        Optionally provide aliases for them in the return. Example::
+        Optionally provide aliases for them in the return. Subsequent
+        calls will *replace* any previous field limits. Example::
 
             queryset.only('title', 'author', 'date')
             queryset.only('title:title_t', 'date:pubyear_i')
 
         """
         qs_copy = self._clone()
-        qs_copy.field_list.extend(args)
+        # *replace* any existing field list with the current values
+        qs_copy.field_list = list(args)
         for key, value in kwargs.items():
             qs_copy.field_list.append('%s:%s' % (key, value))
 

parasolr/tests/test_query.py

@@ -182,10 +182,10 @@ def test_only(self):
         # original field list unchanged
         assert not sqs.field_list
 
-        # chaining is equivalent
-        fields_sqs = sqs.only('title').only('author').only('date')
+        # chaining is not equivalent, but *replaces*
+        fields_sqs = sqs.only('title').only('author')
         # field list refined
-        assert fields_sqs.field_list == only_fields
+        assert fields_sqs.field_list == ['author']
         # original field list unchanged
         assert not sqs.field_list