From 7762a7df42e63a7b93b4ac97801233c19abf9a7e Mon Sep 17 00:00:00 2001
From: Aarni Koskela <aarni.koskela@andersinno.fi>
Date: Tue, 22 Mar 2016 09:52:40 +0200
Subject: [PATCH] Implement and use an IOError ignoring ManyRelatedField for
 images

---
 democracy/views/hearing.py |  6 +++++-
 democracy/views/section.py |  6 ++++--
 democracy/views/utils.py   | 24 ++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/democracy/views/hearing.py b/democracy/views/hearing.py
index 6d9064e6..759d9d21 100644
--- a/democracy/views/hearing.py
+++ b/democracy/views/hearing.py
@@ -13,6 +13,7 @@
 from democracy.views.hearing_comment import HearingCommentSerializer
 from democracy.views.label import LabelSerializer
 from democracy.views.section import SectionFieldSerializer
+from democracy.views.utils import IOErrorIgnoringManyRelatedField
 
 from .hearing_report import HearingReport
 
@@ -42,7 +43,10 @@ def get_queryset(self):
 
 class HearingSerializer(serializers.ModelSerializer):
     labels = LabelSerializer(many=True, read_only=True)
-    images = HearingImageSerializer.get_field_serializer(many=True, read_only=True)
+    images = HearingImageSerializer.get_field_serializer(
+        many=True, read_only=True,
+        many_field_class=IOErrorIgnoringManyRelatedField
+    )
     sections = serializers.SerializerMethodField()
     comments = HearingCommentSerializer.get_field_serializer(many=True, read_only=True)
     commenting = EnumField(enum_type=Commenting)
diff --git a/democracy/views/section.py b/democracy/views/section.py
index 8f6b0df0..dabcb840 100644
--- a/democracy/views/section.py
+++ b/democracy/views/section.py
@@ -4,10 +4,10 @@
 from democracy.models import Hearing, Section, SectionImage
 from democracy.utils.drf_enum_field import EnumField
 from democracy.views.base import AdminsSeeUnpublishedMixin, BaseImageSerializer
+from democracy.views.utils import IOErrorIgnoringManyRelatedField
 
 
 class SectionImageSerializer(BaseImageSerializer):
-
     class Meta:
         model = SectionImage
         fields = ['title', 'url', 'width', 'height', 'caption']
@@ -17,7 +17,9 @@ class SectionSerializer(serializers.ModelSerializer):
     """
     Serializer for section instance.
     """
-    images = SectionImageSerializer.get_field_serializer(many=True, read_only=True)
+    images = SectionImageSerializer.get_field_serializer(
+        many=True, read_only=True, many_field_class=IOErrorIgnoringManyRelatedField
+    )
     type = serializers.SlugRelatedField(slug_field='identifier', read_only=True)
     type_name_singular = serializers.SlugRelatedField(source='type', slug_field='name_singular', read_only=True)
     type_name_plural = serializers.SlugRelatedField(source='type', slug_field='name_plural', read_only=True)
diff --git a/democracy/views/utils.py b/democracy/views/utils.py
index 7708d4a6..487032e6 100644
--- a/democracy/views/utils.py
+++ b/democracy/views/utils.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from functools import lru_cache
 
+from django.db.models.query import QuerySet
 from rest_framework import serializers
 from rest_framework.relations import ManyRelatedField, MANY_RELATION_KWARGS
 
@@ -35,3 +36,26 @@ def get_field_serializer_class(cls, many_field_class=ManyRelatedField):
     def get_field_serializer(cls, **kwargs):
         many_field_class = kwargs.pop("many_field_class", ManyRelatedField)
         return cls.get_field_serializer_class(many_field_class=many_field_class)(**kwargs)
+
+
+class IOErrorIgnoringManyRelatedField(ManyRelatedField):
+    """
+    A ManyRelatedField that ignores IOErrors occurring during iterating the children.
+
+    This is mainly useful for images that are referenced in the database but do not exist
+    on the server (where constructing them requires accessing them to populate the width
+    and height fields).
+    """
+    def to_representation(self, iterable):
+        out = []
+        if isinstance(iterable, QuerySet):
+            iterable = iterable.iterator()
+        while True:
+            try:
+                value = next(iterable)
+                out.append(self.child_relation.to_representation(value))
+            except StopIteration:
+                break
+            except IOError:
+                continue
+        return out