# Demo
# model.py
class a_model(models.Model):
        a_and_b = models.ForeignKey(b_model, related_name='a_and_b',)

class b_model(models.Model):
        pass

# Demo
# model.py
@admin.register(a_model)
class a_admin(admin.ModelAdmin):
    pass

class a_inline(admin.TabularInline):
    model = a_model
    show_change_link = True

@admin.register(b_model)
class b_admin(admin.ModelAdmin):
    inlines = ['a_inline']