Change render_to_csv_response to return a StreamingHttpResponse.

The old behaviour is available by setting the keyword argument
`streaming` to `False`.

Also cleans up the README a bit.

Fixes #86, Fixes #87

README.rst

@@ -27,13 +27,13 @@ installation
 Run::
 
    pip install django-queryset-csv
-   
+
 Supports Python 2.6 and 2.7, Django >= 1.5.
 
 usage
 -----
 Perform all filtering and field authorization in your view using ``.filter()`` and ``.values()``.
-Then, use ``render_to_csv_response`` to turn a queryset into a respone with a CSV attachment.
+Then, use ``render_to_csv_response`` to turn a queryset into a response with a CSV attachment.
 Pass it a ``QuerySet`` or ``ValuesQuerySet`` instance::
 
   from djqscsv import render_to_csv_response
@@ -42,6 +42,14 @@ Pass it a ``QuerySet`` or ``ValuesQuerySet`` instance::
     qs = Foo.objects.filter(bar=True).values('id', 'bar')
     return render_to_csv_response(qs)
 
+If you need to write the CSV to a file you can use ``write_csv`` instead::
+
+  from djqscsv import write_csv
+
+  qs = Foo.objects.filter(bar=True).values('id', 'bar')
+  with open('foo.csv', 'w') as csv_file:
+    write_csv(qs, csv_file)
+
 foreign keys
 ------------
 
@@ -77,6 +85,10 @@ This module exports two functions that write CSVs, ``render_to_csv_response`` an
 - ``use_verbose_names`` - (default: ``True``) A boolean determining whether to use the django field's ``verbose_name``, or to use it's regular field name as a column header. Note that if a given field is found in the ``field_header_map``, this value will take precendence.
 - ``field_order`` - (default: ``None``) A list of fields to determine the sort order. This list need not be complete: any fields not specified will follow those in the list with the order they would have otherwise used.
 
+In addition to the above arguments, ``render_to_csv_response`` takes the
+following optional keyword argument:
+- ``streaming`` - (default: ``True``) A boolean determining whether to use ``StreamingHttpResponse`` instead of the normal ``HttpResponse``.
+
 The remaining keyword arguments are *passed through* to the csv writer. For example, you can export a CSV with a different delimiter.
 
 views.py::

djqscsv/djqscsv.py

@@ -4,24 +4,32 @@
 
 from django.core.exceptions import ValidationError
 from django.utils.text import slugify
-from django.http import HttpResponse
+from django.http import HttpResponse, StreamingHttpResponse
 
 from django.utils import six
 
 """ A simple python package for turning django models into csvs """
 
 # Keyword arguments that will be used by this module
 # the rest will be passed along to the csv writer
-DJQSCSV_KWARGS = {'field_header_map': None,
-                  'field_serializer_map': None,
-                  'use_verbose_names': True,
-                  'field_order': None}
+DJQSCSV_KWARGS = {
+    'field_header_map', 'field_serializer_map', 'use_verbose_names',
+    'field_order', 'streaming'}
 
 
 class CSVException(Exception):
     pass
 
 
+class _Echo(object):
+    """An object that implements just the write method of the file-like
+    interface.
+    """
+    def write(self, value):
+        """Write the value by returning it, instead of storing in a buffer."""
+        return value
+
+
 def render_to_csv_response(queryset, filename=None, append_datestamp=False,
                            **kwargs):
     """
@@ -36,19 +44,33 @@ def render_to_csv_response(queryset, filename=None, append_datestamp=False,
         filename = generate_filename(queryset,
                                      append_datestamp=append_datestamp)
 
-    response = HttpResponse(content_type='text/csv')
+    if not kwargs.get('streaming', True):
+        response = HttpResponse(content_type='text/csv')
+        write_csv(queryset, response, **kwargs)
+    else:
+        response = StreamingHttpResponse(
+            _iter_csv(queryset, _Echo(), **kwargs),
+            content_type='text/csv')
+
     response['Content-Disposition'] = 'attachment; filename=%s;' % filename
     response['Cache-Control'] = 'no-cache'
 
-    write_csv(queryset, response, **kwargs)
-
     return response
 
 
 def write_csv(queryset, file_obj, **kwargs):
+    """
+    Writes CSV data to a file object based on the contents of the queryset.
+    """
+    # Force iteration over all rows so they all get written to the file
+    for _ in _iter_csv(queryset, file_obj, **kwargs):
+        pass
+
+
+def _iter_csv(queryset, file_obj, **kwargs):
     """
     The main worker function. Writes CSV data to a file object based on the
-    contents of the queryset.
+    contents of the queryset and yields each row.
     """
 
     # process keyword arguments to pull out the ones used by this function
@@ -64,7 +86,7 @@ def write_csv(queryset, file_obj, **kwargs):
             csv_kwargs[key] = val
 
     # add BOM to support CSVs in MS Excel (for Windows only)
-    file_obj.write(b'\xef\xbb\xbf')
+    yield file_obj.write(b'\xef\xbb\xbf')
 
     # the CSV must always be built from a values queryset
     # in order to introspect the necessary fields.
@@ -134,11 +156,11 @@ def write_csv(queryset, file_obj, **kwargs):
         merged_header_map.update(dict((k, k) for k in extra_columns))
     merged_header_map.update(field_header_map)
 
-    writer.writerow(merged_header_map)
+    yield writer.writerow(merged_header_map)
 
     for record in values_qs:
         record = _sanitize_record(field_serializer_map, record)
-        writer.writerow(record)
+        yield writer.writerow(record)
 
 
 def generate_filename(queryset, append_datestamp=False):

test_app/djqscsv_tests/tests/test_csv_creation.py

@@ -298,7 +298,7 @@ def test_render_to_csv_response_no_filename(self):
         response = djqscsv.render_to_csv_response(self.qs,
                                                   use_verbose_names=False)
         self.assertEqual(response['Content-Type'], 'text/csv')
-        self.assertMatchesCsv(response.content.splitlines(),
+        self.assertMatchesCsv(''.join(response.streaming_content).splitlines(),
                               self.FULL_PERSON_CSV_NO_VERBOSE)
 
         self.assertRegexpMatches(response['Content-Disposition'],
@@ -309,6 +309,15 @@ def test_render_to_csv_response(self):
                                                   filename="test_csv",
                                                   use_verbose_names=False)
         self.assertEqual(response['Content-Type'], 'text/csv')
+        self.assertMatchesCsv(''.join(response.streaming_content).splitlines(),
+                              self.FULL_PERSON_CSV_NO_VERBOSE)
+
+    def test_render_to_csv_response_non_streaming(self):
+        response = djqscsv.render_to_csv_response(self.qs,
+                                                  filename="test_csv",
+                                                  use_verbose_names=False,
+                                                  streaming=False)
+        self.assertEqual(response['Content-Type'], 'text/csv')
         self.assertMatchesCsv(response.content.splitlines(),
                               self.FULL_PERSON_CSV_NO_VERBOSE)
 
@@ -319,7 +328,7 @@ def test_render_to_csv_response_other_delimiter(self):
                                                   delimiter='|')
 
         self.assertEqual(response['Content-Type'], 'text/csv')
-        self.assertMatchesCsv(response.content.splitlines(),
+        self.assertMatchesCsv(''.join(response.streaming_content).splitlines(),
                               self.FULL_PERSON_CSV_NO_VERBOSE,
                               delimiter="|")
 
@@ -330,5 +339,6 @@ def test_render_to_csv_fails_on_delimiter_mismatch(self):
                                                   delimiter='|')
 
         self.assertEqual(response['Content-Type'], 'text/csv')
-        self.assertNotMatchesCsv(response.content.splitlines(),
-                                 self.FULL_PERSON_CSV_NO_VERBOSE)
+        self.assertNotMatchesCsv(
+            ''.join(response.streaming_content).splitlines(),
+            self.FULL_PERSON_CSV_NO_VERBOSE)