Add django-polymorphic integration docs

Author: fdintino

docs/index.rst

@@ -25,6 +25,7 @@ Contents
    quickstart
    why_use
    customization
+   integrations
    contributing
    changelog
 

docs/integrations.rst

@@ -0,0 +1,88 @@
+============
+Integrations
+============
+
+django-polymorphic
+==================
+
+Quickstart
+----------
+
+Support for `django-polymorphic`_ is currently in beta. To use polymorphic
+inlines with django-nested-admin follow the steps for
+`setting up django-polymorphic admin inline integration`_. The instructions
+are identical with django-nested-admin, except that the classes you would
+normally import from ``polymorphic.admin`` should instead be imported from
+``nested_admin`` and the classes themselves should be prefixed with
+``Nested`` For example:
+
+.. code-block:: python
+
+    # Instead of these imports
+    from django.contrib.admin import ModelAdmin
+    from polymorphic.admin import (
+        PolymorphicInlineSupportMixin, StackedPolymorphicInline)
+
+    # One should import:
+    from nested_admin import (
+        NestedModelAdmin,
+        NestedPolymorphicInlineSupportMixin, NestedStackedPolymorphicInline)
+
+The polymorphic inlines used with django-nested-admin can have other inlines
+nested inside them, or even other polymorphic inlines. The only requirement
+is that all ModelAdmin and InlineAdmin classes inherit from the appropriate
+nested version.
+
+.. _django-polymorphic: https://django-polymorphic.readthedocs.io/en/stable/index.html
+.. _setting up django-polymorphic admin inline integration: https://django-polymorphic.readthedocs.io/en/stable/admin.html#inline-models
+
+Example
+-------
+
+.. code-block:: python
+
+    from django.contrib import admin
+    import nested_admin
+    from .models import (
+        Store, Customer, GuestCustomer, LoggedInCustomer, OrderItem, Product, WishListItem,
+        Order, WishList, Payment, CreditCardPayment, BankPayment)
+
+    class PaymentInline(nested_admin.NestedStackedPolymorphicInline):
+        model = Payment
+        class CreditCardPaymentInline(nested_admin.NestedStackedPolymorphicInline.Child):
+            model = CreditCardPayment
+        class BankPayment(nested_admin.NestedStackedPolymorphicInline.Child):
+            model = BankPayment
+        child_inlines = (CreditCardPaymentInline, BankPayment)
+
+    class ProductInline(nested_admin.NestedStackedInline):
+        model = Product
+
+    class WishListItemInline(nested_admin.NestedStackedInline):
+        model = WishListItem
+        sortable_field_name = 'position'
+
+    class WishListInline(nested_admin.NestedStackedInline):
+        model = WishList
+        inlines = [WishListItemInline]
+
+    class OrderItemInline(nested_admin.NestedStackedInline):
+        model = OrderItem
+
+    class OrderInline(nested_admin.NestedTabularInline):
+        model = Order
+        inlines = [OrderItemInline, PaymentInline]
+
+    class CustomerInline(nested_admin.NestedStackedPolymorphicInline):
+        model = Customer
+        inlines = [OrderInline]
+        class GuestCustomerInline(nested_admin.NestedStackedPolymorphicInline.Child):
+            model = GuestCustomer
+        class LoggedInCustomerInline(nested_admin.NestedStackedPolymorphicInline.Child):
+            model = LoggedInCustomer
+            inlines = [WishListInline]
+        child_inlines = (GuestCustomerInline, LoggedInCustomerInline)
+
+    @admin.register(Store)
+    class StoreAdmin(nested_admin.NestedPolymorphicModelAdmin):
+        inlines = [CustomerInline]