Rails holds some conventions that enforcement of data integrity should be done in the application, not in the database. For example, Rails even supports some database designs that cannot use foreign keys, such as Polymorphic Associations. Basically, Rails conventions have treated the database as a static data storage device, not an active RDBMS. Rails 2.0 … Read more
Table B has rows whose foreign key references the primary key value of the Table A row you are trying to delete so deleting it would violate the integrity of your database. You could include ON DELETE CASCADE in your foreign key definition. With that, when you delete an entry from Table A, any entries … Read more
It’s not possible to install Foreign Keys to abstract models in Django. You can however install Foreign Keys to a non abstract base class. The only limitation is that the reverse Foreign Key relation will return the base class instances. You can circumvent this limitation by using django-polymorphic. Django Polymorphic allows you to query the … Read more
Internal dependencies between tables and / or other objects are never bound to the object name. Internally, every object is stored in a catalog table and the OID (internal primary key) of the object is used for everything else. Accordingly, a FOREIGN KEY reference is stored in the catalog tables pg_constraint (the constraint itself incl. … Read more
create_user INT UNSIGNED ZEROFILL cannot reference id INT, because these count as different data types for purposes of foreign key reference. Make them the same data type. The only data type difference that is permitted between columns in a foreign key relationship is length of a varchar. For example, VARCHAR(10) can reference VARCHAR(20) or vice-versa. … Read more
Instead of defining “schema” level ForeignKey constraints create a custom foreign condition; pass what columns you’d like to use as “foreign keys” and the primaryjoin to relationship. You have to manually define the primaryjoin because: By default, this value is computed based on the foreign key relationships of the parent and child tables (or association … Read more
In the SQLite Documentation it says: … “an index should be created on the child key columns of each foreign key constraint” ie. the index is not automatically created, but you should create one in every instance.
I was looking for a solution to the same problem and ran across this question… ended up solving it myself. The OP might not be interested anymore but this could still be useful to someone. from functools import partial from django.forms import MediaDefiningClass class ModelAdminWithForeignKeyLinksMetaclass(MediaDefiningClass): def __getattr__(cls, name): def foreign_key_link(instance, field): target = getattr(instance, field) … Read more
Yes. Ensures that you don’t have an orphan (entry with no parent), and depending on usage, if you define a cascading delete, when a parent is deleted, all its children will also be deleted. Disadvantage would be a slight performance hit just like any other foreign key.
I haven’t tried this, but it seems that since Django 1.0 you can do something like: class Foo(models.Model): foo = models.ForeignKey(Bar, to_field=’bar’) Documentation for this is here.