add support to the documents api to only serve selected fields

src/documents/serialisers.py

@@ -7,6 +7,28 @@ from .models import Correspondent, Tag, Document, Log, DocumentType
 from .parsers import is_mime_type_supported
 
 
+# https://www.django-rest-framework.org/api-guide/serializers/#example
+class DynamicFieldsModelSerializer(serializers.ModelSerializer):
+    """
+    A ModelSerializer that takes an additional `fields` argument that
+    controls which fields should be displayed.
+    """
+
+    def __init__(self, *args, **kwargs):
+        # Don't pass the 'fields' arg up to the superclass
+        fields = kwargs.pop('fields', None)
+
+        # Instantiate the superclass normally
+        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)
+
+        if fields is not None:
+            # Drop any fields that are not specified in the `fields` argument.
+            allowed = set(fields)
+            existing = set(self.fields)
+            for field_name in existing - allowed:
+                self.fields.pop(field_name)
+
+
 class CorrespondentSerializer(serializers.ModelSerializer):
 
     document_count = serializers.IntegerField(read_only=True)
@@ -90,7 +112,7 @@ class DocumentTypeField(serializers.PrimaryKeyRelatedField):
         return DocumentType.objects.all()
 
 
-class DocumentSerializer(serializers.ModelSerializer):
+class DocumentSerializer(DynamicFieldsModelSerializer):
 
     correspondent = CorrespondentField(allow_null=True)
     tags = TagsField(many=True)

src/documents/views.py

@@ -131,6 +131,17 @@ class DocumentViewSet(RetrieveModelMixin,
         "added",
         "archive_serial_number")
 
+    def get_serializer(self, *args, **kwargs):
+        fields_param = self.request.query_params.get('fields', None)
+        if fields_param:
+            fields = fields_param.split(",")
+        else:
+            fields = None
+        serializer_class = self.get_serializer_class()
+        kwargs.setdefault('context', self.get_serializer_context())
+        kwargs.setdefault('fields', fields)
+        return serializer_class(*args, **kwargs)
+
     def update(self, request, *args, **kwargs):
         response = super(DocumentViewSet, self).update(
             request, *args, **kwargs)