POST request to update data fields - AngularJS, Django - angularjs

Question

I have two models:
class Lecture(models.Model):
lecture_no = models.IntegerField(null=True)
title = models.CharField(max_length=128, unique=True, null=True)
youtubeLink = models.CharField(max_length=128, unique=True, null=True)
course = models.ForeignKey(Course, null=True)
keywords = models.TextField(max_length=300, null=True)
#Could add Next Rerun Date & Time
def __str__(self):
return self.title
class Notes(models.Model):
notes = models.TextField(null=True)
lecture = models.ForeignKey(Lecture, null=True, related_name='lecture')
def __str__(self):
return self.notes
These serializers:
class NotesSerializer(serializers.ModelSerializer):
lecture = LectureSerializer(read_only=True, many=True)
class Meta:
model = Notes
fields = ('id', 'notes', 'lecture')
class KeywordSerializer(serializers.ModelSerializer):
lecture = LectureSerializer(read_only=True, many=True)
class Meta:
model = Keyword
fields = ('id', 'notes', 'lecture')
and these views:
class LectureViewSet(viewsets.ModelViewSet):
serializer_class = LectureSerializer
def get_queryset(self):
course_id = self.request.query_params.get('course',False)
if course_id:
lectures = Lecture.objects.filter(course=course_id)
else:
lectures = Lecture.objects.all()
return lectures
class NotesViewSet(viewsets.ModelViewSet):
queryset = Notes.objects.all()
serializer_class = NotesSerializer
and I'm trying to make it so that I can update the "notes" field for a specific lecture. Currently I'm using a POST http request:
saveNotes: function(notes, lecture_id, callback) {
$http({
method: 'POST',
url: apiRoute + 'notes/',
data: {
"notes": notes,
"lecture_id": lecture_id
}
}).success(callback);
}
But this just adds a new row to the database every time. How do you update fields instead?
Thanks