How to serialize a Join query set from several tables in Django Rest Framework

Question

Sometimes, frameworks make things more complicated instead of simplifying them. I would like to serialize a join like this one

queryset = Cities.objects.raw("SELECT 1 as id, cities.name as ci, states.name as s, countries.name as co FROM cities JOIN states ON states.id = cities.state_id LEFT OUTER JOIN countries ON countries.id = states.country_id WHERE cities.name = %s", [city])

or like this one, if raw queries are not recommended

city = self.request.query_params.get("cityname")

As you can see this is a reverse join. The idea is to serialize a result set like this one

0:  
name:   "Guadalajara"
state:  "Castilla La Mancha"
country:    "Spain"

1:
name: "Guadalajara"
state: "Jalisco"
coutry: "Mexico"

Two cities having the same name but belonging to different states and countries. I need this to implement a sort of autocomplete feature. This is actually pseudocode but it gives an idea about the kind of JSON result I would like to get.

I read the documentation and I searched the internet, I found nothing clear about how to do this.

I'm new to Django and I'm completely lost, this is a simple task that would be easy to do manually, but I have no idea about how to achieve this using Django Rest Framework (or any other tool from Django).

Any help would be really appreciated.

Answer 1

The DRF provides generic views to serialize a collection of objects using a particular model. Let's say you have a model called City like this:

from django.db import models

class City(models.Model):
    name = models.CharField()
    state = models.CharField()
    country = models.CharField()

And a serializer like this one:

from rest_framework import serializers

class CitySerializer(serializers.ModelSerializer):
    class Meta:
         model = City
         fields = ['name', 'state', 'country']

In your view you'd need to inherit from generics.ListAPIView like so:

from rest_framwork.generics import ListAPIView

class CityList(ListAPIView):
    serializer_class = CitySerializer

    def get_queryset(self):
        return City.objects.filter(
            name=self.request.query_params.get('cityname')
        )

The ListAPIView class serializes a list of City instances for you quite easily. You can find further explanations here: https://www.django-rest-framework.org/api-guide/generic-views/#listapiview

Answer 2

I found a solution, I don't know if it's the best solution but it worked for me and I would like to share it. If someone find a better way to do this, you are welcome to suggest changes.

My model:

""" The following 3 models deal with tables that already exist in the database """
class Countries(models.Model):
    name = models.CharField(max_length=100)
    iso3 = models.CharField(max_length=3, blank=True, null=True)
    iso2 = models.CharField(max_length=2, blank=True, null=True)
    phonecode = models.CharField(max_length=255, blank=True, null=True)
    capital = models.CharField(max_length=255, blank=True, null=True)
    currency = models.CharField(max_length=255, blank=True, null=True)
    currency_symbol = models.CharField(max_length=255, blank=True, null=True)
    tld = models.CharField(max_length=255, blank=True, null=True)
    native = models.CharField(max_length=255, blank=True, null=True)
    region = models.CharField(max_length=255, blank=True, null=True)
    subregion = models.CharField(max_length=255, blank=True, null=True)
    timezones = models.TextField(blank=True, null=True)
    translations = models.TextField(blank=True, null=True)
    latitude = models.DecimalField(max_digits=10, decimal_places=8, blank=True, null=True)
    longitude = models.DecimalField(max_digits=11, decimal_places=8, blank=True, null=True)
    emoji = models.CharField(max_length=191, blank=True, null=True)
    emojiu = models.CharField(db_column='emojiU', max_length=191, blank=True, null=True)  # Field name made lowercase.
    created_at = models.DateTimeField(blank=True, null=True)
    updated_at = models.DateTimeField()
    flag = models.IntegerField()
    wikidataid = models.CharField(db_column='wikiDataId', max_length=255, blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'countries'


class States(models.Model):
    name = models.CharField(max_length=255)
    country = models.ForeignKey(Countries, models.DO_NOTHING)
    country_code = models.CharField(max_length=2)
    fips_code = models.CharField(max_length=255, blank=True, null=True)
    iso2 = models.CharField(max_length=255, blank=True, null=True)
    latitude = models.DecimalField(max_digits=10, decimal_places=8, blank=True, null=True)
    longitude = models.DecimalField(max_digits=11, decimal_places=8, blank=True, null=True)
    created_at = models.DateTimeField(blank=True, null=True)
    updated_at = models.DateTimeField()
    flag = models.IntegerField()
    wikidataid = models.CharField(db_column='wikiDataId', max_length=255, blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'states'


class Cities(models.Model):
    name = models.CharField(max_length=255)
    state = models.ForeignKey('States', models.DO_NOTHING)
    state_code = models.CharField(max_length=255)
    country = models.ForeignKey('Countries', models.DO_NOTHING)
    country_code = models.CharField(max_length=2)
    latitude = models.DecimalField(max_digits=10, decimal_places=8)
    longitude = models.DecimalField(max_digits=11, decimal_places=8)
    created_at = models.DateTimeField()
    updated_at = models.DateTimeField()
    flag = models.IntegerField()
    wikidataid = models.CharField(db_column='wikiDataId', max_length=255, blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'cities'

Sure, the database comes from this project, if someone needs it https://dr5hn.github.io/countries-states-cities-database/

Here's my View

class CityViewSet(viewsets.ReadOnlyModelViewSet):
    serializer_class = CitiesSerializer
    def get_queryset(self):
        city = self.request.query_params.get("cityname")
        queryset = Cities.objects.filter(name__startswith=city)
        return queryset

And finally my serializers.py

""" Fields:
'name','country','country-code','fips_code','iso2','latitude','longitude','created_at','updated_at','flag','wikidataid'
"""
class StatesSerializer(serializers.ModelSerializer):    
    class Meta:
        model = States
        fields = ['name', 'iso2']

""" Fields 
'name','iso3','iso2','phonecode','capital','currency_symbol','tld','native','region','subregion','timezones','translations','latitude','longitude','emoji','emojiu','created_at','updated_at','flag','wikidataid'
"""
class CountriesSerializer(serializers.ModelSerializer):
    class Meta:
        model = Countries
        fields = ['name', 'iso2', ]#'translations']


"""Fields:
'name','state','state_code','country','country_code','latitude','longitude','created_at','updated_at','flag','wikidataid'
"""
class CitiesSerializer(serializers.ModelSerializer):
    state = StatesSerializer(many=False)
    country = CountriesSerializer(many=False)

    class Meta:
        model = Cities
        fields = ['name', 'state', 'country', 'latitude', 'longitude']

With this code I will get the right expected JSon output. Sure it must be read by a proper forntend, like JQuery, Vue or even Vanilla JavaScript, but the object of the question is fullfilled.

If you know a better way, again, don't hesitate.