From 04ae8cb4f655204cfbb09f1c68cc0e3d6c71d108 Mon Sep 17 00:00:00 2001
From: James Graham <J.Graham@software.ac.uk>
Date: Tue, 31 Mar 2020 15:43:33 +0100
Subject: [PATCH] feat: Recursively flatten serializers for CSV export

---
 people/serializers.py  |  3 +++
 people/views/export.py | 46 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/people/serializers.py b/people/serializers.py
index 85e1c27..bd501d5 100644
--- a/people/serializers.py
+++ b/people/serializers.py
@@ -31,6 +31,9 @@ class PersonExportSerializer(serializers.ModelSerializer):
 
         
 class RelationshipSerializer(serializers.ModelSerializer):
+    source = PersonSerializer()
+    target = PersonSerializer()
+
     class Meta:
         model = models.Relationship
         fields = [
diff --git a/people/views/export.py b/people/views/export.py
index 6e62b26..8e58ea9 100644
--- a/people/views/export.py
+++ b/people/views/export.py
@@ -5,6 +5,8 @@ from django.contrib.auth.mixins import LoginRequiredMixin
 from django.http import HttpResponse
 from django.views.generic.list import BaseListView
 
+from rest_framework.serializers import BaseSerializer
+
 from .. import models, serializers
 
 
@@ -12,14 +14,54 @@ class CsvExportView(LoginRequiredMixin, BaseListView):
     model = None
     serializer_class = None
 
+    @classmethod
+    def flatten_data(cls, data,
+                     sub_type: typing.Type = dict,
+                     sub_value_accessor: typing.Callable = lambda x: x.items()) -> typing.Dict:
+        """
+        Flatten a dictionary so that subdictionaryies become a series of `key[.subkey[.subsubkey ...]]` entries
+        in the top level dictionary.
+
+        Works for other data structures (e.g. DRF Serializers) by providing suitable values for the
+        `sub_type` and `sub_value_accessor` parameters.
+
+        :param data: Dictionary or other data structure to flatten
+        :param sub_type: Type to recursively flatten
+        :param sub_value_accessor: Function to access keys and values contained within sub_type.
+        """
+        data_out = {}
+
+        for key, value in sub_value_accessor(data):
+            if isinstance(value, sub_type):
+                # Recursively flatten nested structures of type `sub_type`
+                sub_flattened = cls.flatten_data(value,
+                                                 sub_type=sub_type,
+                                                 sub_value_accessor=sub_value_accessor).items()
+
+                # Enter recursively flattened values into result dictionary
+                for sub_key, sub_value in sub_flattened:
+                    # Keys in result dictionary are of format `key[.subkey[.subsubkey ...]]`
+                    data_out[f'{key}.{sub_key}'] = sub_value
+                    
+            else:
+                data_out[key] = value
+
+        return data_out
+
     def render_to_response(self, context: typing.Dict) -> HttpResponse:
         response = HttpResponse(content_type='text/csv')
         response['Content-Disposition'] = f'attachment; filename="{self.get_context_object_name(self.object_list)}.csv"'
         
         serializer = self.serializer_class(self.get_queryset(), many=True)
-        writer = csv.DictWriter(response, fieldnames=self.serializer_class.Meta.fields)
+        columns = self.flatten_data(serializer.child.fields,
+                                    sub_type=BaseSerializer,
+                                    sub_value_accessor=lambda x: x.fields.items())
+        
+        writer = csv.DictWriter(response, fieldnames=columns)
         writer.writeheader()
-        writer.writerows(serializer.data)
+        
+        for row in serializer.data:
+            writer.writerow(self.flatten_data(row))
             
         return response