Access field from intermediary model in Django Rest Framework - django

Question

Having a hard time trying to access a field from an intermediary model in DRF.
Let's see the related models:
class School(models.Model):
created = models.DateTimeField(auto_now_add=True)
name = models.CharField(max_length=50, verbose_name=_(u'Name'))
staff_order = models.ManyToManyField(settings.AUTH_USER_MODEL, verbose_name=_(u'Staff ordering'), through='StaffOrder', related_name='school_staff_order')
class User(AbstractUser):
phone = models.CharField(max_length=20, blank=True, null=True)
address = models.CharField(max_length=150, blank=True, null=True)
about_me = models.CharField(max_length=200, blank=True, null=True)
REQUIRED_FIELDS = ['email']
def __unicode__(self):
return u'{0}'.format(self.username)
class StaffOrder(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL)
school = models.ForeignKey(School)
order = models.PositiveSmallIntegerField(default=0, verbose_name=_(u'Staff ordering for this school'))
class Meta:
verbose_name_plural = _(u'Staff ordering')
Now what I'm expecting is being able to read order field from StaffOrder in when returning a QuerySet for users (StaffSerializer). Here are the Serializers:
class StaffRoleSerializer(serializers.ModelSerializer):
class Meta:
model = StaffOrder
fields = (
'order',
)
class StaffSerializer(serializers.ModelSerializer):
username = serializers.CharField(max_length=75, required=True)
email = serializers.CharField(max_length=75, required=True)
order = StaffRoleSerializer(source='school_staff_order')
class Meta:
model = User
What is returned in order for the StaffSerializer is a Manager, instead of the order field from the StaffOrder model related with this User.
A JSON expected response for Staff would be something like this:
[
{
"username": "Denise",
"email": "deniseburton#maximind.com",
"order": 9
},
{
"username": "Ina",
"email": "inaburton#maximind.com",
"order": 4
}
]
I'd love to be able to also write this value from the serializer, but I can do that in the Viewset, but I really need to read this value in the Serializer itself...any idea what I'm missing here?

Answer 1

First you have to understand that one user can have many staff orders. In your models you have defined it that way.
To get the json output you have specified in your question you need to query the StaffOrder objects instead of users.
class StaffOrderSerializer(serializers.ModelSerializer):
username = serializers.CharField(source='user.username')
email = serializers.CharField(source='user.email')
class Meta:
model = StaffOrder
fields = ('order', )
Use this serializer class in a list view:
class StaffOrderListApi(generics.ListAPIView):
serializer_class = StaffOrderSerializer
def get_queryset(self):
# using distinct because same user can have multiple staff orders
# based on your example it seems you want distinct users
return StaffOrder.objects.all().distinct('user')
This will get you exactly the json you want.