Make the admin `base_model` setting optional.

It can be detected using get_base_polymorphic_model()

docs/admin.rst

@@ -63,7 +63,7 @@ The models are taken from :ref:`advanced-features`.
 
     class ModelAChildAdmin(PolymorphicChildModelAdmin):
         """ Base admin class for all child models """
-        base_model = ModelA
+        base_model = ModelA  # Optional, explicitly set here.
 
         # By using these `base_...` attributes instead of the regular ModelAdmin `form` and `fieldsets`,
         # the additional fields of the child models are automatically added to the admin form.
@@ -75,13 +75,13 @@ The models are taken from :ref:`advanced-features`.
 
     @admin.register(ModelB)
     class ModelBAdmin(ModelAChildAdmin):
-        base_model = ModelB
+        base_model = ModelB  # Explicitly set here!
         # define custom features here
 
 
     @admin.register(ModelC)
     class ModelCAdmin(ModelBAdmin):
-        base_model = ModelC
+        base_model = ModelC  # Explicitly set here!
         show_in_index = True  # makes child model admin visible in main admin site
         # define custom features here
 
@@ -89,7 +89,7 @@ The models are taken from :ref:`advanced-features`.
     @admin.register(ModelA)
     class ModelAParentAdmin(PolymorphicParentModelAdmin):
         """ The parent model admin """
-        base_model = ModelA
+        base_model = ModelA  # Optional, explicitly set here.
         child_models = (ModelB, ModelC)
         list_filter = (PolymorphicChildModelFilter,)  # This is optional.
 

docs/third-party.rst

@@ -69,7 +69,7 @@ The admin :ref:`admin example <admin-example>` becomes:
 
 
     class ModelAChildAdmin(PolymorphicChildModelAdmin, VersionAdmin):
-        base_model = ModelA
+        base_model = ModelA  # optional, explicitly set here.
         base_form = ...
         base_fieldsets = (
             ...
@@ -83,7 +83,7 @@ The admin :ref:`admin example <admin-example>` becomes:
 
 
     class ModelAParentAdmin(VersionAdmin, PolymorphicParentModelAdmin):
-        base_model = ModelA
+        base_model = ModelA  # optional, explicitly set here.
         child_models = (
             (ModelB, ModelBAdmin),
             (ModelC, ModelCAdmin),

example/pexp/admin.py

@@ -4,13 +4,13 @@ from pexp.models import *
 
 
 class ProjectAdmin(PolymorphicParentModelAdmin):
-    base_model = Project
+    base_model = Project  # Can be set explicitly.
     list_filter = (PolymorphicChildModelFilter,)
     child_models = (Project, ArtProject, ResearchProject)
 
 
 class ProjectChildAdmin(PolymorphicChildModelAdmin):
-    base_model = Project
+    base_model = Project  # Can be set explicitly.
 
     # On purpose, only have the shared fields here.
     # The fields of the derived model should still be displayed.
@@ -27,13 +27,12 @@ admin.site.register(ResearchProject, ProjectChildAdmin)
 
 
 class UUIDModelAAdmin(PolymorphicParentModelAdmin):
-    base_model = UUIDModelA
     list_filter = (PolymorphicChildModelFilter,)
     child_models = (UUIDModelA, UUIDModelB)
 
 
 class UUIDModelAChildAdmin(PolymorphicChildModelAdmin):
-    base_model = UUIDModelA
+    pass
 
 
 admin.site.register(UUIDModelA, UUIDModelAAdmin)
@@ -42,13 +41,12 @@ admin.site.register(UUIDModelC, UUIDModelAChildAdmin)
 
 
 class ProxyAdmin(PolymorphicParentModelAdmin):
-    base_model = ProxyBase
     list_filter = (PolymorphicChildModelFilter,)
     child_models = (ProxyA, ProxyB)
 
 
 class ProxyChildAdmin(PolymorphicChildModelAdmin):
-    base_model = ProxyBase
+    pass
 
 
 admin.site.register(ProxyBase, ProxyAdmin)

polymorphic/admin/childadmin.py

@@ -8,6 +8,7 @@ from django.urls import resolve
 from django.utils import six
 from django.utils.translation import ugettext_lazy as _
 
+from polymorphic.utils import get_base_polymorphic_model
 from ..admin import PolymorphicParentModelAdmin
 
 
@@ -25,8 +26,6 @@ class PolymorphicChildModelAdmin(admin.ModelAdmin):
     * It adds the base model to the template lookup paths.
     * It allows to set ``base_form`` so the derived class will automatically include other fields in the form.
     * It allows to set ``base_fieldsets`` so the derived class will automatically display any extra fields.
-
-    The ``base_model`` attribute must be set.
     """
     base_model = None
     base_form = None
@@ -34,6 +33,12 @@ class PolymorphicChildModelAdmin(admin.ModelAdmin):
     extra_fieldset_title = _("Contents")  # Default title for extra fieldset
     show_in_index = False
 
+    def __init__(self, model, admin_site, *args, **kwargs):
+        super(PolymorphicChildModelAdmin, self).__init__(model, admin_site, *args, **kwargs)
+
+        if self.base_model is None:
+            self.base_model = get_base_polymorphic_model(model)
+
     def get_form(self, request, obj=None, **kwargs):
         # The django admin validation requires the form to have a 'class Meta: model = ..'
         # attribute, or it will complain that the fields are missing.

polymorphic/admin/parentadmin.py

@@ -18,6 +18,7 @@ from django.utils.http import urlencode
 from django.utils.safestring import mark_safe
 from django.utils.translation import ugettext_lazy as _
 
+from polymorphic.utils import get_base_polymorphic_model
 from .forms import PolymorphicModelChoiceForm
 
 
@@ -36,9 +37,8 @@ class ChildAdminNotRegistered(RuntimeError):
 class PolymorphicParentModelAdmin(admin.ModelAdmin):
     """
     A admin interface that can displays different change/delete pages, depending on the polymorphic model.
-    To use this class, two variables need to be defined:
+    To use this class, one attribute need to be defined:
 
-    * :attr:`base_model` should
     * :attr:`child_models` should be a list of (Model, Admin) tuples
 
     Alternatively, the following methods can be implemented:
@@ -50,7 +50,7 @@ class PolymorphicParentModelAdmin(admin.ModelAdmin):
     The derived models should *not* register the ModelAdmin, but instead it should be returned by :func:`get_child_models`.
     """
 
-    #: The base model that the class uses
+    #: The base model that the class uses (auto-detected if not set explicitly)
     base_model = None
 
     #: The child models that should be displayed
@@ -71,6 +71,9 @@ class PolymorphicParentModelAdmin(admin.ModelAdmin):
         super(PolymorphicParentModelAdmin, self).__init__(model, admin_site, *args, **kwargs)
         self._is_setup = False
 
+        if self.base_model is None:
+            self.base_model = get_base_polymorphic_model(model)
+
     def _lazy_setup(self):
         if self._is_setup:
             return