Creating a ForeignKey Across Databases in Django 2.0
2018-05-15 12:24 (6 years ago)
ytyng
※ This does not mean creating constraints in an RDB. It simply means creating a ForeignKey field that works for now.
In Django 2.0, when you try to create a ForeignKey to a model that uses a different database, you get the following error when saving:
Cannot assign "<YourModel>": the current database router prevents this relation.
This error prevents saving.
In such cases, you can return True in the allow_relation method of the database router:
def allow_relation(self, obj1, obj2):
if {obj1._meta.app_label, obj2._meta.app_label} \
== {'my_app_1', 'my_app_2'}:
return True
↑ This might work if you set everything to True, but if you want to judge by app_label, it would look something like this.
The default is None
https://docs.djangoproject.com/en/2.0/topics/db/multi-db/#allow_relation
For the model that uses the ForeignKey:
related_model = models.ForeignKey(
YourModel, on_delete=models.DO_NOTHING,
db_constraint=False, null=True, blank=True)
If you set db_constraint=False like this (otherwise, you cannot migrate),
it will work as a ForeignKey.
However, as indicated in the code, there will be no constraints on the DB.
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