documentation: invalid foreign key and select_related

[adriannye@…]

Let's say Book has a foreign key to Author.
If there is a invalid id in the Author field of any Book instance, then these two queries get a different set
of Book instances:

Book.objects.all()
Book.objects.select_related('author').all()

The second query will omit the Book objects that have an author field that points nowhere.
This surprised me since I thought of select_related as only ADDING information to a query. In this situation it also REMOVES information.

Invalid keys can happen with a database that does not have referential integrity checking like mysql with MyISAM.

[Luke Plant]

I'm going to WONTIFX this - there are probably any number of bugs that will be caused by a corrupt database. The model layer assumes your Model class reflects your database correctly, and if you've used a foreign key when its possible for the data to not be a foreign key, your model is incorrect. This is similar to bugs that would occur if you've got an incorrect max_length on CharField. Either your database needs to have referential integrity or your business logic needs to ensure integrity.