CODEWITHSUNDEEP
pythondjangodjango-oscar
Jake Rankin
Jake Rankin

Reputation: 744

Forked django-oscar app with custom model unable to migrate

I am using django-oscar and forked some of the apps to use a custom model.

Specifically with the catalogue model. By default there are products, product types and product categories. I am trying to extent the model to have a collections table, and to have each product be associated with a collection.

I want to make the relationship so that when a collection is deleted all associated products are deleted, but so that deleting a product does not delete a collection.

Aside from adding a new collection table, I extent the product table to have a multiplier field (which will contain an integer used to multiply the wholesale price...if there is a better way to do this please inform) and a foreign key to the collections table.

Based on my understanding everything looks good. This is my models.py from the forked catalogue app:

from django.db import models

class Collection(models.Model):
    name = models.CharField(max_length=50)
    prod_category = models.CharField(max_length=50)
    description = models.TextField()
    manufacturer = models.TextField()
    num_products = models.IntegerField()
    image_url = models.URLField()

from oscar.apps.catalogue.abstract_models import AbstractProduct

class Product(AbstractProduct):
    collection = models.ForeignKey(Collection, on_delete=models.CASCADE)
    multiplier = models.DecimalField(max_digits=2, decimal_places=1)

from oscar.apps.catalogue.models import *

When I do makemigrations via manage.py, after asking for default values (something I will deal with later) it seems fine.

When running migrate however, I get the following error output:

Running migrations:
  Applying catalogue.0014_auto_20181211_1617...Traceback (most recent call last):
  File "/home/mysite/lib/python3.7/Django-2.1.3-py3.7.egg/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
psycopg2.IntegrityError: insert or update on table "catalogue_product" violates foreign key constraint "catalogue_product_collection_id_e8789e0b_fk_catalogue"
DETAIL:  Key (collection_id)=(1) is not present in table "catalogue_collection".

Is this because I need to add a field collection_id?

Upvotes: 0

Views: 312

Answers (1)

solarissmoke
solarissmoke

Reputation: 31474

The problem is that you have specified a default value that doesn't exist. I am guessing that when asked to specify default values for the migration, you entered 1 for the collection. The problem is that there is no Collection object with such an ID in the database, which is why the migration fails.

You either need to:

  1. Create a Collection object with the default ID you specified before attempting to add the overridden product model.

  2. Make the foreign key to Collection nullable, so that you don't need a default value.

Upvotes: 1

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