Django Admin: OneToOne Relation as an Inline?

It’s perfectly possible to use an inline for a OneToOne relationship. However, the actual field defining the relationship has to be on the inline model, not the parent one – in just the same way as for a ForeignKey. Switch it over and it will work.

Edit after comment: you say the parent model is already registered with the admin: then unregister it and re-register.

from original.satchmo.admin import ProductAdmin

class MyProductInline(admin.StackedInline):
    model = MyProduct

class ExtendedProductAdmin(ProductAdmin):
    inlines = ProductAdmin.inlines + (MyProductInline,)

admin.site.unregister(Product)
admin.site.register(Product, ExtendedProductAdmin)

Update 2020 (Django 3.1.1)

This method is still working but some types has changed in new Django version since inlines in ExtendedProductAdmin should now be added as list and not tuple, like this:

class ExtendedProductAdmin(ProductAdmin):
    inlines = ProductAdmin.inlines + [MyProductInline]

Or you will get this error:

    inlines = ProductAdmin.inlines + (MyProductInline,)
TypeError: can only concatenate list (not "tuple") to list