Fix for 974

docs/changelog.rst

@@ -9,6 +9,7 @@ Please refer to :doc:`release notes<release_notes>`.
 - Fix issue where declared Resource fields not defined in ``fields`` are still imported (#1702)
 - Added customizable ``MediaStorage`` (#1708)
 - Relocated admin integration section from advanced_usage.rst into new file (#1713)
+- Fix slow export with ForeignKey id (#1717)
 
 4.0.0-beta.2 (2023-12-09)
 -------------------------

import_export/resources.py

@@ -13,6 +13,7 @@
 from django.core.paginator import Paginator
 from django.db import connections, router
 from django.db.models import fields
+from django.db.models.fields.related import ForeignKey
 from django.db.models.query import QuerySet
 from django.db.transaction import TransactionManagementError, set_rollback
 from django.utils.encoding import force_str
@@ -1196,9 +1197,17 @@ def field_from_django_field(cls, field_name, django_field, readonly):
 
         FieldWidget = cls.widget_from_django_field(django_field)
         widget_kwargs = cls.widget_kwargs_for_field(field_name, django_field)
+
+        attribute = field_name
+        column_name = field_name
+        # To solve #974
+        if isinstance(django_field, ForeignKey) and "__" not in column_name:
+            attribute += "_id"
+            widget_kwargs["key_is_id"] = True
+
         field = cls.DEFAULT_RESOURCE_FIELD(
-            attribute=field_name,
-            column_name=field_name,
+            attribute=attribute,
+            column_name=column_name,
             widget=FieldWidget(**widget_kwargs),
             readonly=readonly,
             default=django_field.default,

import_export/widgets.py

@@ -476,9 +476,17 @@ class Meta:
         related object, default to False
     """
 
-    def __init__(self, model, field="pk", use_natural_foreign_keys=False, **kwargs):
+    def __init__(
+        self,
+        model,
+        field="pk",
+        use_natural_foreign_keys=False,
+        key_is_id=False,
+        **kwargs,
+    ):
         self.model = model
         self.field = field
+        self.key_is_id = key_is_id
         self.use_natural_foreign_keys = use_natural_foreign_keys
         super().__init__(**kwargs)
 
@@ -528,7 +536,10 @@ def clean(self, value, row=None, **kwargs):
                 return self.model.objects.get_by_natural_key(*value)
             else:
                 lookup_kwargs = self.get_lookup_kwargs(value, row, **kwargs)
-                return self.get_queryset(value, row, **kwargs).get(**lookup_kwargs)
+                obj = self.get_queryset(value, row, **kwargs).get(**lookup_kwargs)
+                if self.key_is_id:
+                    return obj.id
+                return obj
         else:
             return None
 
@@ -551,6 +562,10 @@ def render(self, value, obj=None):
           ``coerce_to_string`` has no effect on the return value.
         """
         self._obj_deprecation_warning(obj)
+
+        if self.key_is_id:
+            return value or ""
+
         if value is None:
             return ""
 

tests/core/tests/test_resources/test_resources.py

@@ -289,6 +289,24 @@ def test_export(self):
             dataset = self.resource.export(queryset=Book.objects.all())
             self.assertEqual(len(dataset), 1)
 
+    @ignore_widget_deprecation_warning
+    def test_export_with_foreign_keys(self):
+        """
+        Test that export() containing foreign keys doesn't generate
+        extra query for every row.
+        Fixes #974
+        """
+        author = Author.objects.create()
+        self.book.author = author
+        self.book.save()
+        Book.objects.create(name="Second book", author=Author.objects.create())
+        Book.objects.create(name="Third book", author=Author.objects.create())
+
+        with self.assertNumQueries(3):
+            dataset = self.resource.export(Book.objects.prefetch_related("categories"))
+            self.assertEqual(dataset.dict[0]["author"], author.pk)
+            self.assertEqual(len(dataset), 3)
+
     @ignore_widget_deprecation_warning
     def test_export_iterable(self):
         with self.assertNumQueries(2):