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I'd like to set up a ForeignKey field in a django model which points to another table some of the time. But I want it to be okay to insert an id into this field which refers to an entry in the other table which might not be there. So if the row exists in the other table, I'd like to get all the benefits of the ForeignKey relationship. But if not, I'd like this treated as just a number.
Is this possible? Is this what Generic relations are for?
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To make a foreign key field in Django non-nullable, you need to provide a default value for the existing rows. You might want to also provide a default value for new rows. Adding a default is easy when the value is a string or a date, but not when you have to provide the ID of another object.
The PROTECT argument of the ForeignKey on_delete option prevents the referenced object from being deleted if it already has an object referencing it in the database. Put simply, Django will prevent a post from deletion if it already has comments.
ForeignKey does not allow null values.
ForeignKey is a Django ORM field-to-column mapping for creating and working with relationships between tables in relational databases. ForeignKey is defined within the django. db. models. related module but is typically referenced from django.
This question was asked a long time ago, but for newcomers there is now a built in way to handle this by setting db_constraint=False on your ForeignKey:
https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ForeignKey.db_constraint
customer = models.ForeignKey('Customer', db_constraint=False)
or if you want to to be nullable as well as not enforcing referential integrity:
customer = models.ForeignKey('Customer', null=True, blank=True, db_constraint=False)
We use this in cases where we cannot guarantee that the relations will get created in the right order.
EDIT: update link
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