port generic field to 4.2

netbox/utilities/generics/field.py

@@ -0,0 +1,143 @@
+from collections import defaultdict
+
+from django.contrib.contenttypes.models import ContentType
+from django.core.exceptions import ObjectDoesNotExist
+from django.db.models.fields import Field
+from django.db.models.fields.mixins import FieldCacheMixin
+from django.utils.functional import cached_property
+
+
+class GenericArrayForeignKey(FieldCacheMixin, Field):
+    """
+    Provide a generic many-to-many relation through an array field
+    """
+
+    many_to_many = True
+    many_to_one = False
+    one_to_many = False
+    one_to_one = False
+
+    def __init__(self, field, for_concrete_model=True):
+        super().__init__(editable=False)
+        self.field = field
+        self.for_concrete_model = for_concrete_model
+        self.is_relation = True
+
+    def contribute_to_class(self, cls, name, **kwargs):
+        super().contribute_to_class(cls, name, private_only=True, **kwargs)
+        # GenericForeignKey is its own descriptor.
+        setattr(cls, self.attname, self)
+
+    @cached_property
+    def cache_name(self):
+        return self.name
+
+    def get_cache_name(self):
+        return self.cache_name
+
+    def _get_ids(self, instance):
+        return getattr(instance, self.field)
+
+    def get_content_type_by_id(self, id=None, using=None):
+        return ContentType.objects.db_manager(using).get_for_id(id)
+
+    def get_content_type_of_obj(self, obj=None):
+        return ContentType.objects.db_manager(obj._state.db).get_for_model(
+            obj, for_concrete_model=self.for_concrete_model
+        )
+
+    def get_content_type_for_model(self, using=None, model=None):
+        return ContentType.objects.db_manager(using).get_for_model(
+            model, for_concrete_model=self.for_concrete_model
+        )
+
+    def get_prefetch_querysets(self, instances, querysets=None):
+        custom_queryset_dict = {}
+        if querysets is not None:
+            for queryset in querysets:
+                ct_id = self.get_content_type_for_model(
+                    model=queryset.query.model, using=queryset.db
+                ).pk
+                if ct_id in custom_queryset_dict:
+                    raise ValueError(
+                        "Only one queryset is allowed for each content type."
+                    )
+                custom_queryset_dict[ct_id] = queryset
+
+        # For efficiency, group the instances by content type and then do one
+        # query per model
+        fk_dict = defaultdict(set)  # type id, db -> model ids
+        for instance in instances:
+            for step in self._get_ids(instance):
+                for ct_id, fk_val in step:
+                    fk_dict[(ct_id, instance._state.db)].add(fk_val)
+
+        rel_objects = []
+        for (ct_id, db), fkeys in fk_dict.items():
+            if ct_id in custom_queryset_dict:
+                rel_objects.extend(custom_queryset_dict[ct_id].filter(pk__in=fkeys))
+            else:
+                ct = self.get_content_type_by_id(id=ct_id, using=db)
+                rel_objects.extend(ct.get_all_objects_for_this_type(pk__in=fkeys))
+
+        # reorganize objects to fix usage
+        items = {
+            (self.get_content_type_of_obj(obj=rel_obj).pk, rel_obj.pk, rel_obj._state.db): rel_obj
+            for rel_obj in rel_objects
+        }
+        lists = []
+        lists_keys = {}
+        for instance in instances:
+            data = []
+            lists.append(data)
+            lists_keys[instance] = id(data)
+            for step in self._get_ids(instance):
+                nodes = []
+                for ct, fk in step:
+                    if rel_obj := items.get((ct, fk, instance._state.db)):
+                        nodes.append(rel_obj)
+                data.append(nodes)
+
+        return (
+            lists,
+            lambda obj: id(obj),
+            lambda obj: lists_keys[obj],
+            True,
+            self.cache_name,
+            False,
+        )
+
+    def __get__(self, instance, cls=None):
+        if instance is None:
+            return self
+        rel_objects = self.get_cached_value(instance, default=None)
+        expected_ids = self._get_ids(instance)
+        # check cache actual
+        if rel_objects is not None:
+            actual = [
+                [
+                    (self.get_content_type_of_obj(obj=item).id, item.pk)
+                    for item in step
+                ]
+                for step in rel_objects
+            ]
+            if expected_ids == actual:
+                return rel_objects
+        # reload value
+        if expected_ids is None:
+            self.set_cached_value(instance, rel_objects)
+            return rel_objects
+        data = []
+        for step in self._get_ids(instance):
+            rel_objects = []
+            for ct_id, pk_val in step:
+                ct = self.get_content_type_by_id(id=ct_id, using=instance._state.db)
+                try:
+                    rel_obj = ct.get_object_for_this_type(pk=pk_val)
+                    rel_objects.append(rel_obj)
+                except ObjectDoesNotExist:
+                    pass
+            data.append(rel_objects)
+        self.set_cached_value(instance, data)
+        return data
+