From 817e49c1b9ea34c6aaebe9186e3b51195552d550 Mon Sep 17 00:00:00 2001
From: Christoph Buelter <christoph.buelter@myshopradio.de>
Date: Tue, 26 Sep 2017 13:43:18 +0200
Subject: [PATCH 1/2] Use the serializer context as optional params source.

This allows passing omit/fields values to drf-dynamic-fields from a lower level API, useful when creating serializers manually, e.g. inside other serializers.
---
 drf_dynamic_fields/__init__.py | 33 ++++++++++++++++++-----
 tests/test_mixins.py           | 48 ++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 7 deletions(-)

diff --git a/drf_dynamic_fields/__init__.py b/drf_dynamic_fields/__init__.py
index e19124d..ec67922 100644
--- a/drf_dynamic_fields/__init__.py
+++ b/drf_dynamic_fields/__init__.py
@@ -10,6 +10,27 @@ class DynamicFieldsMixin(object):
     which fields should be displayed.
     """
 
+    def _collect_params(self, request):
+        """Params can be passed via the GET query or the serializer context.
+
+        Both sources are merged into a unique set, with the context
+        taking predecence over query parameters.
+
+        """
+        params = getattr(
+            request, 'query_params', getattr(request, 'GET', None)
+        )
+
+        if params is not None:
+            params = params.copy()
+
+            for param_name in ('omit', 'fields'):
+                param_value = self.context.get(param_name, None)
+                if param_value is not None:
+                    params[param_name] = param_value
+
+        return params
+
     @property
     def fields(self):
         """
@@ -29,7 +50,8 @@ def fields(self):
         # Only filter if this is the root serializer, or if the parent is the
         # root serializer with many=True
         is_root = self.root == self
-        parent_is_list_root = self.parent == self.root and getattr(self.parent, 'many', False)
+        parent_is_list_root = (self.parent == self.root and
+                               getattr(self.parent, 'many', False))
         if not (is_root or parent_is_list_root):
             return fields
 
@@ -39,13 +61,10 @@ def fields(self):
             warnings.warn('Context does not have access to request')
             return fields
 
-        # NOTE: drf test framework builds a request object where the query
-        # parameters are found under the GET attribute.
-        params = getattr(
-            request, 'query_params', getattr(request, 'GET', None)
-        )
+        params = self._collect_params(request)
+
         if params is None:
-            warnings.warn('Request object does not contain query paramters')
+            warnings.warn('Request object does not contain query parameters')
 
         try:
             filter_fields = params.get('fields', None).split(',')
diff --git a/tests/test_mixins.py b/tests/test_mixins.py
index 6b7718a..c540c7f 100644
--- a/tests/test_mixins.py
+++ b/tests/test_mixins.py
@@ -169,3 +169,51 @@ def test_as_nested_serializer(self):
                 ],
             }
         )
+
+    def test_pass_params_via_serializer_context(self):
+        """
+        Params can solely (or additionally) be passed via serializer context.
+        """
+        rf = RequestFactory()
+        request = rf.get('/api/v1/schools/1/')
+        context = {
+            'request': request,
+            'omit': 'request_info',
+        }
+        serializer = TeacherSerializer(context=context)
+
+        self.assertEqual(
+            set(serializer.fields.keys()),
+            set(('id',))
+        )
+
+    def test_serializer_context_overwrites_query_params(self):
+        """
+        Params passed via context take precedence over query_params.
+        """
+        rf = RequestFactory()
+        request = rf.get('/api/v1/schools/1/?fields=request_info')
+        context = {
+            'request': request,
+            'fields': 'id',
+        }
+        serializer = TeacherSerializer(context=context)
+
+        self.assertEqual(
+            set(serializer.fields.keys()),
+            set(('id',))
+        )
+
+    def test_no_params_passed_at_all(self):
+        """
+        Specifying neither query_params nor context params should not fail.
+        """
+        rf = RequestFactory()
+        request = rf.get('/api/v1/schools/1/')
+        context = {'request': request}
+        serializer = TeacherSerializer(context=context)
+
+        self.assertEqual(
+            set(serializer.fields.keys()),
+            set(('id', 'request_info'))
+        )

From 4323232fe71392a5e0f0554092b794b46161045d Mon Sep 17 00:00:00 2001
From: Christoph Buelter <christoph.buelter@myshopradio.de>
Date: Tue, 26 Sep 2017 13:51:07 +0200
Subject: [PATCH 2/2] Update README about using serializer context to pass
 parameters.

---
 README.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/README.rst b/README.rst
index b2c71e9..a7e1294 100644
--- a/README.rst
+++ b/README.rst
@@ -137,6 +137,15 @@ pass in the request through the context:
     serializer = EventSerializer(events, many=True, context={'request': request})
 
 
+In addition to using query parameters to pass ``omit`` and ``fields``, the
+serializer context can be used as well (also taking precedence over the query):
+
+.. sourcecode:: python
+
+    events = Event.objects.all()
+    context = {'request': request, 'omit': 'id,name'}
+    serializer = EventSerializer(events, many=True, context=context)
+
 Testing
 -------