Fixed #12674 -- provide a way to override admin validation

Moved admin validation code to classes and have those be class
attributes to the ModelAdmin classes.

django/contrib/admin/options.py

@@ -10,6 +10,7 @@
 from django.contrib.admin import widgets, helpers
 from django.contrib.admin.util import (unquote, flatten_fieldsets, get_deleted_objects,
     model_format_dict, NestedObjects)
+from django.contrib.admin import validation
 from django.contrib.admin.templatetags.admin_static import static
 from django.contrib import messages
 from django.views.decorators.csrf import csrf_protect
@@ -87,6 +88,14 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
     readonly_fields = ()
     ordering = None
 
+    # validation
+    validator_class = validation.BaseValidator
+
+    @classmethod
+    def validate(cls, model):
+        validator = cls.validator_class()
+        validator.validate(cls, model)
+
     def __init__(self):
         overrides = FORMFIELD_FOR_DBFIELD_DEFAULTS.copy()
         overrides.update(self.formfield_overrides)
@@ -371,6 +380,9 @@ class ModelAdmin(BaseModelAdmin):
     actions_on_bottom = False
     actions_selection_counter = True
 
+    # validation
+    validator_class = validation.ModelAdminValidator
+
     def __init__(self, model, admin_site):
         self.model = model
         self.opts = model._meta
@@ -1447,6 +1459,9 @@ class InlineModelAdmin(BaseModelAdmin):
     verbose_name_plural = None
     can_delete = True
 
+    # validation
+    validator_class = validation.InlineValidator
+
     def __init__(self, parent_model, admin_site):
         self.admin_site = admin_site
         self.parent_model = parent_model

django/contrib/admin/sites.py

@@ -66,12 +66,6 @@ def register(self, model_or_iterable, admin_class=None, **options):
         if not admin_class:
             admin_class = ModelAdmin
 
-        # Don't import the humongous validation code unless required
-        if admin_class and settings.DEBUG:
-            from django.contrib.admin.validation import validate
-        else:
-            validate = lambda model, adminclass: None
-
         if isinstance(model_or_iterable, ModelBase):
             model_or_iterable = [model_or_iterable]
         for model in model_or_iterable:
@@ -94,8 +88,8 @@ def register(self, model_or_iterable, admin_class=None, **options):
                     options['__module__'] = __name__
                     admin_class = type("%sAdmin" % model.__name__, (admin_class,), options)
 
-                # Validate (which might be a no-op)
-                validate(admin_class, model)
+                if admin_class is not ModelAdmin and settings.DEBUG:
+                    admin_class.validate(model)
 
                 # Instantiate the admin class to save in the registry
                 self._registry[model] = admin_class(model, self)