Improve prefetching for single/optional fields by not prefetching the…

… whole table

strawberry_django/fields/field.py

@@ -31,6 +31,7 @@
     ReverseOneToOneDescriptor,
 )
 from django.db.models.manager import BaseManager
+from django.db.models.query import MAX_GET_RESULTS
 from django.db.models.query_utils import DeferredAttribute
 from strawberry import UNSET, relay
 from strawberry.annotation import StrawberryAnnotation
@@ -282,30 +283,27 @@ def qs_hook(qs: models.QuerySet):  # type: ignore
 
             def qs_hook(qs: models.QuerySet):  # type: ignore
                 qs = self.get_queryset(qs, info, **kwargs)
-                # Don't use qs.first() if the queryset is optimized by prefetching.
-                # Calling first in that case would disregard the prefetched results, because first implicitly
-                # adds a limit to the query
-                if is_optimized_by_prefetching(qs):
-                    return next(iter(qs), None)
                 return qs.first()
 
         else:
 
             def qs_hook(qs: models.QuerySet):
                 qs = self.get_queryset(qs, info, **kwargs)
-                # See comment above about qs.first(), the same applies for get()
+                # Don't use qs.get() if the queryset is optimized by prefetching.
+                # Calling first in that case would disregard the prefetched results, because first implicitly
+                # adds a limit to the query
                 if is_optimized_by_prefetching(qs):
                     # mimic behavior of get()
-                    qs_len = len(
-                        qs
-                    )  # the queryset is already prefetched, no issue with just using len()
+                    # the queryset is already prefetched, no issue with just using len()
+                    qs_len = len(qs)
                     if qs_len == 0:
                         raise qs.model.DoesNotExist(
                             f"{qs.model._meta.object_name} matching query does not exist."
                         )
                     if qs_len != 1:
                         raise qs.model.MultipleObjectsReturned(
-                            f"get() returned more than one {qs.model._meta.object_name} -- it returned {qs_len}!"
+                            f"get() returned more than one {qs.model._meta.object_name} -- it returned "
+                            f"{qs_len if qs_len < MAX_GET_RESULTS else f'more than {qs_len - 1}'}!"
                         )
                     return qs[0]
                 return qs.get()

strawberry_django/pagination.py

@@ -6,6 +6,7 @@
 from django.db import DEFAULT_DB_ALIAS
 from django.db.models import Count, QuerySet, Window
 from django.db.models.functions import RowNumber
+from django.db.models.query import MAX_GET_RESULTS
 from strawberry.types import Info
 from strawberry.types.arguments import StrawberryArgument
 from strawberry.types.unset import UNSET, UnsetType
@@ -343,6 +344,19 @@ def get_queryset(
         if self.is_paginated:
             return queryset
 
+        # Add implicit pagination if this field is not a list
+        # that way when first() / get() is called on the QuerySet it does not cause extra queries
+        if not pagination and not (
+            self.is_list or self.is_paginated or self.is_connection
+        ):
+            if self.is_optional:
+                # first() applies order by pk if not ordered
+                if not queryset.ordered:
+                    queryset = queryset.order_by("pk")
+                pagination = OffsetPaginationInput(offset=0, limit=1)
+            else:
+                pagination = OffsetPaginationInput(offset=0, limit=MAX_GET_RESULTS)
+
         return self.apply_pagination(
             queryset,
             pagination,