The default behavior of the ListAPIView (code below) is to serialize all Report objects and the nested Log objects per Report object. What if I only want the latest Log object to be displayed per Report? How do I go about doing that?
# models.py
class Log(models.Model):
# ...
report = models.ForeignKey(Report)
timestamp = models.DateTimeField(default=datetime.datetime.now)
class Report(models.Model):
code = models.CharField(max_length=32, unique=True)
description = models.TextField()
# serializers.py
class LogSerializer(serializers.ModelSerializer):
class Meta:
model = Log
class ReportSerializer(serializers.ModelSerializer):
log_set = LogSerializer(many=True, read_only=True)
class Meta:
model = Report
fields = ('code', 'description', 'log_set')
# views.py
class ReportListView(generics.ListAPIView):
queryset = Report.objects.all()
serializer_class = ReportSerializer
I know I can do this by using a SerializerMethodField, but this can be a potentially expensive operation, since there will be an extra SQL query to retrieve the appropriate Log object for each Report object.
class ReportSerializer(serializers.ModelSerializer):
latest_log = serializers.SerializerMethodField()
class Meta:
model = Report
def get_latest_log(self, obj):
try:
latest_log = Log.objects.filter(report_id=obj.id).latest('timestamp')
except Log.DoesNotExist:
latest_log = None
return latest_log
If I have 1000 report objects, there will be 1000 extra queries if I want to render them all. How do I avoid those extra queries besides using pagination? Can anyone point me to the right direction? Thanks!
EDIT: Regarding the possible duplicate tag, the link alone provided by Mark did not completely clear up the picture for me. Todor's answer was more clear.