Django Rest Framework: Implementing Many-to-Many relationship in

ghz 15hours ago ⋅ 4 views

Django Rest Framework: Implementing Many-to-Many relationship in Serializer

I'm using the Django Rest Framework to create a custom API for my Movies model which is defined as follows:

models.py

from django.db import models


class Genres(models.Model):
    genre = models.CharField(max_length = 128, unique = True)

class Movies(models.Model):
    popularity = models.FloatField()
    director = models.CharField(max_length = 128)
    genres = models.ManyToManyField(Genres, related_name = 'movies')
    imdb_score = models.FloatField()
    movie_name = models.CharField(max_length = 500)

Now, in my application, each genre can have multiple movie instances and vice versa. As a result, there is a Many-to-Many relationship between the Genres model and the Movies model. I want to allow the admin to chose multiple genres for a particular movie while posting new Movies instances at the API endpoint.

serializers.py

from shoppy.models import Movies, Genres
from rest_framework import serializers


class GenresSerializer(serializers.ModelSerializer):

    class Meta:
        model = Genres

class MoviesSerializer(serializers.ModelSerializer):


    class Meta:
        model = Movies
        fields = ('popularity', 'director', 'imdb_score', 'genres',
                        'movie_name')

views.py

from shoppy.models import Movies
from rest_framework import viewsets
from shoppy.serializers import MoviesSerializer


class MovieViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows users to be viewed or edited.
    """
    queryset = Movies.objects.all()
    serializer_class = MoviesSerializer

urls.py

from django.conf.urls import url, include
from rest_framework import routers
from shoppy import views

router = routers.DefaultRouter()
router.register(r'movies', views.MovieViewSet)
# Wire up our API using automatic URL routing.
# Additionally, we include login URLs for the browsable API.
urlpatterns = [
    url(r'^', include(router.urls)),
    url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework'))
]

However, I'm encountering the following error:

Exception Type: OperationalError at /movies/
Exception Value: no such table: shoppy_genres

What seems to be wrong with my code?

Answer

The error you're encountering, OperationalError: no such table: shoppy_genres, is due to the fact that the database table for the Genres model has not been created yet. This is a common issue when you've defined new models or made changes to the database schema but haven't run the necessary migrations to apply the changes to the database.

Solution: Apply Database Migrations

Django uses migrations to handle changes to the database schema, such as adding new tables or modifying existing ones. To resolve this issue, you need to generate and apply the migrations for your models.

Follow these steps:

1. Generate Migrations

First, make sure you've created the migrations for your models by running the following command:

python manage.py makemigrations

This will create migration files based on the changes you made to the models (in your case, the Movies and Genres models). You should see a new migration file in the migrations folder of your app.

2. Apply the Migrations

Once the migrations are generated, you need to apply them to the database to create the necessary tables. Run:

python manage.py migrate

This will apply the migrations and create the tables in the database, including the table for the Genres model (shoppy_genres).

3. Verify the Tables

You can verify that the tables have been created by checking your database or using Django's dbshell (if you're using a supported database):

python manage.py dbshell

If you're using SQLite (the default for development), you can inspect the database directly. Alternatively, you can use a database tool like DB Browser for SQLite to open the db.sqlite3 file.

4. Testing the API

After applying the migrations, the shoppy_genres table should be created, and you should be able to make POST requests to the /movies/ endpoint to create new Movies instances, including selecting multiple genres.

You can use the Django admin interface or a tool like Postman to test your API endpoints.

Additional Notes:

  • Migrations: If you change models (like adding fields, models, etc.), always remember to run makemigrations and migrate to ensure your database stays in sync with the code.

  • Admin Interface: If you're using Django's admin interface and want to be able to select multiple genres for a movie, make sure you register your models in admin.py like so:

    from django.contrib import admin
from shoppy.models import Movies, Genres

admin.site.register(Movies)
admin.site.register(Genres)

This will allow you to manage your Movies and Genres directly through Django's admin interface, and you should be able to select multiple genres for each movie.

Conclusion:

To fix the error no such table: shoppy_genres, you need to generate and apply migrations using the makemigrations and migrate commands. This will create the necessary database tables for the Genres model and allow your API to function properly.

#py