Allow ForeignKey to a parent class when using inlines

[sil]

At the moment, if you have a hierarchy:

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField()

(as per ​http://www.djangoproject.com/documentation/model-api/#multi-table-inheritance), it doesn't interact all that well with inlined ForeignKeyed models. Imagine you had:

class Owner:
    name = models.CharField(max_length=100)
    place = models.ForeignKey(Place)

(so a Place can have multiple Owners). This also works fine with Restaurants, because every Restaurant is-a Place. However, if you want to inline the Owners:

class OwnerInline(admin.TabularInline): 
    model = Owner
    extra = 5

class PlaceAdmin(admin.ModelAdmin):
    model = Place
    inlines = [OwnerInline]

then this won't work; if you try and create a Restaurant, you get a complaint that Owner has no ForeignKey to Restaurant (because technically it doesn't). This is because (new)forms._get_foreign_key checks that the ForeignKey points to this model itself, where it should really be checking whether the ForeignKey points to this model or any of its ancestor classes. The attached patch rectifies this.

[sil]

mrph. Code from above in code formatting. Sorry.

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField?()

class Owner:
    name = models.CharField(max_length=100)
    place = models.ForeignKey(Place)

class OwnerInline(admin.TabularInline):
    model = Owner
    extra = 5

class PlaceAdmin(admin.ModelAdmin):
    model = Place
    inlines = [OwnerInline]

[Brian Rosner]

Fixed ticket description formatting.

[sil]

Updated to handle fail

[sil]

Updated patch to handle the OneToOneField value being null when you're first adding a Restaurant, which blows up because it's not a nullable field (since it's a PK) but doesn't have a value (because the Restaurant isn't saved yet). Sorry.

[Brian Rosner]

Don't change the stage. That is reserved for ticket triagers and committers. The ticket itself is accepted, you don't need to do that when you upload a new patch. The needs_better_patch is meant for that :)

[sil]

Cool -- I figured that the newer patch wasn't reviewed :) no problem!

[Brian Rosner]

It is likely [8165] has fixed this. Can someone verify? Perhaps a test case should be ordered :)

[Arnaud Rebts]

It seems to be working now if the ForeinKey is in the direct super class, but not if it's in a higher class.

So, this is working:

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField()

class Owner(models.Model):
    name = models.CharField(max_length=100)
    place = models.ForeignKey(Place)

class OwnerInline(admin.TabularInline): 
    model = Owner
    extra = 5

class PlaceAdmin(admin.ModelAdmin):
    model = Place
    inlines = [OwnerInline]

class RestaurantAdmin(admin.ModelAdmin):
    model = Restaurant
    inlines = [OwnerInline]

But not this:

class ItalianRestaurant(Restaurant):
    pass

class ItalianRestaurantAdmin(admin.ModelAdmin):
    model = ItalianRestaurant
    inlines = [OwnerInline]

[Brian Rosner]

(In [8708]) Fixed #7918 -- Allow the foreign key in an inline to be any where in the parent chain. Thanks sil for the report.

[Jacob]

Milestone 1.0 deleted