Fixed #7270 -- Added the ability to follow reverse OneToOneFields in select_related(). Thanks to George Vilches, Ben Davis, and Alex Gaynor for their work on various stages of this patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12307 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -189,7 +189,7 @@ class SingleRelatedObjectDescriptor(object):
     # SingleRelatedObjectDescriptor instance.
     def __init__(self, related):
         self.related = related
-        self.cache_name = '_%s_cache' % related.get_accessor_name()
+        self.cache_name = related.get_cache_name()
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
@@ -319,7 +319,7 @@ class ReverseSingleRelatedObjectDescriptor(object):
             # cache. This cache also might not exist if the related object
             # hasn't been accessed yet.
             if related:
-                cache_name = '_%s_cache' % self.field.related.get_accessor_name()
+                cache_name = self.field.related.get_cache_name()
                 try:
                     delattr(related, cache_name)
                 except AttributeError:

django/db/models/query.py

@@ -1116,6 +1116,29 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
     """
     Helper function that recursively returns an object with the specified
     related attributes already populated.
+
+    This method may be called recursively to populate deep select_related()
+    clauses.
+
+    Arguments:
+     * klass - the class to retrieve (and instantiate)
+     * row - the row of data returned by the database cursor
+     * index_start - the index of the row at which data for this
+       object is known to start
+     * max_depth - the maximum depth to which a select_related()
+       relationship should be explored.
+     * cur_depth - the current depth in the select_related() tree.
+       Used in recursive calls to determin if we should dig deeper.
+     * requested - A dictionary describing the select_related() tree
+       that is to be retrieved. keys are field names; values are
+       dictionaries describing the keys on that related object that
+       are themselves to be select_related().
+     * offset - the number of additional fields that are known to
+       exist in `row` for `klass`. This usually means the number of
+       annotated results on `klass`.
+     * only_load - if the query has had only() or defer() applied,
+       this is the list of field names that will be returned. If None,
+       the full field list for `klass` can be assumed.
     """
     if max_depth and requested is None and cur_depth > max_depth:
         # We've recursed deeply enough; stop now.
@@ -1127,14 +1150,18 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
         # Handle deferred fields.
         skip = set()
         init_list = []
-        pk_val = row[index_start + klass._meta.pk_index()]
+        # Build the list of fields that *haven't* been requested
         for field in klass._meta.fields:
             if field.name not in load_fields:
                 skip.add(field.name)
             else:
                 init_list.append(field.attname)
+        # Retrieve all the requested fields
         field_count = len(init_list)
         fields = row[index_start : index_start + field_count]
+        # If all the select_related columns are None, then the related
+        # object must be non-existent - set the relation to None.
+        # Otherwise, construct the related object.
         if fields == (None,) * field_count:
             obj = None
         elif skip:
@@ -1143,14 +1170,20 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
         else:
             obj = klass(*fields)
     else:
+        # Load all fields on klass
         field_count = len(klass._meta.fields)
         fields = row[index_start : index_start + field_count]
+        # If all the select_related columns are None, then the related
+        # object must be non-existent - set the relation to None.
+        # Otherwise, construct the related object.
         if fields == (None,) * field_count:
             obj = None
         else:
             obj = klass(*fields)
 
     index_end = index_start + field_count + offset
+    # Iterate over each related object, populating any
+    # select_related() fields
     for f in klass._meta.fields:
         if not select_related_descend(f, restricted, requested):
             continue
@@ -1158,12 +1191,51 @@ def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,
             next = requested[f.name]
         else:
             next = None
+        # Recursively retrieve the data for the related object
         cached_row = get_cached_row(f.rel.to, row, index_end, max_depth,
                 cur_depth+1, next)
+        # If the recursive descent found an object, populate the
+        # descriptor caches relevant to the object
         if cached_row:
             rel_obj, index_end = cached_row
             if obj is not None:
+                # If the base object exists, populate the
+                # descriptor cache
                 setattr(obj, f.get_cache_name(), rel_obj)
+            if f.unique:
+                # If the field is unique, populate the
+                # reverse descriptor cache on the related object
+                setattr(rel_obj, f.related.get_cache_name(), obj)
+
+    # Now do the same, but for reverse related objects.
+    # Only handle the restricted case - i.e., don't do a depth
+    # descent into reverse relations unless explicitly requested
+    if restricted:
+        related_fields = [
+            (o.field, o.model)
+            for o in klass._meta.get_all_related_objects()
+            if o.field.unique
+        ]
+        for f, model in related_fields:
+            if not select_related_descend(f, restricted, requested, reverse=True):
+                continue
+            next = requested[f.related_query_name()]
+            # Recursively retrieve the data for the related object
+            cached_row = get_cached_row(model, row, index_end, max_depth,
+                cur_depth+1, next)
+            # If the recursive descent found an object, populate the
+            # descriptor caches relevant to the object
+            if cached_row:
+                rel_obj, index_end = cached_row
+                if obj is not None:
+                    # If the field is unique, populate the
+                    # reverse descriptor cache
+                    setattr(obj, f.related.get_cache_name(), rel_obj)
+                if rel_obj is not None:
+                    # If the related object exists, populate
+                    # the descriptor cache.
+                    setattr(rel_obj, f.get_cache_name(), obj)
+
     return obj, index_end
 
 def delete_objects(seen_objs, using):

django/db/models/query_utils.py

@@ -197,18 +197,28 @@ class DeferredAttribute(object):
         """
         instance.__dict__[self.field_name] = value
 
-def select_related_descend(field, restricted, requested):
+def select_related_descend(field, restricted, requested, reverse=False):
     """
     Returns True if this field should be used to descend deeper for
     select_related() purposes. Used by both the query construction code
     (sql.query.fill_related_selections()) and the model instance creation code
     (query.get_cached_row()).
+
+    Arguments:
+     * field - the field to be checked
+     * restricted - a boolean field, indicating if the field list has been
+       manually restricted using a requested clause)
+     * requested - The select_related() dictionary.
+     * reverse - boolean, True if we are checking a reverse select related
     """
     if not field.rel:
         return False
-    if field.rel.parent_link:
+    if field.rel.parent_link and not reverse:
         return False
-    if restricted and field.name not in requested:
+    if restricted:
+        if reverse and field.related_query_name() not in requested:
+            return False
+        if not reverse and field.name not in requested:
             return False
     if not restricted and field.null:
         return False

django/db/models/related.py

@@ -45,3 +45,6 @@ class RelatedObject(object):
             return self.field.rel.related_name or (self.opts.object_name.lower() + '_set')
         else:
             return self.field.rel.related_name or (self.opts.object_name.lower())
+
+    def get_cache_name(self):
+        return "_%s_cache" % self.get_accessor_name()

django/db/models/sql/compiler.py

@@ -520,7 +520,7 @@ class SQLCompiler(object):
 
         # Setup for the case when only particular related fields should be
         # included in the related selection.
-        if requested is None and restricted is not False:
+        if requested is None:
             if isinstance(self.query.select_related, dict):
                 requested = self.query.select_related
                 restricted = True
@@ -600,6 +600,72 @@ class SQLCompiler(object):
             self.fill_related_selections(f.rel.to._meta, alias, cur_depth + 1,
                     used, next, restricted, new_nullable, dupe_set, avoid)
 
+        if restricted:
+            related_fields = [
+                (o.field, o.model)
+                for o in opts.get_all_related_objects()
+                if o.field.unique
+            ]
+            for f, model in related_fields:
+                if not select_related_descend(f, restricted, requested, reverse=True):
+                    continue
+                # The "avoid" set is aliases we want to avoid just for this
+                # particular branch of the recursion. They aren't permanently
+                # forbidden from reuse in the related selection tables (which is
+                # what "used" specifies).
+                avoid = avoid_set.copy()
+                dupe_set = orig_dupe_set.copy()
+                table = model._meta.db_table
+
+                int_opts = opts
+                alias = root_alias
+                alias_chain = []
+                chain = opts.get_base_chain(f.rel.to)
+                if chain is not None:
+                    for int_model in chain:
+                        # Proxy model have elements in base chain
+                        # with no parents, assign the new options
+                        # object and skip to the next base in that
+                        # case
+                        if not int_opts.parents[int_model]:
+                            int_opts = int_model._meta
+                            continue
+                        lhs_col = int_opts.parents[int_model].column
+                        dedupe = lhs_col in opts.duplicate_targets
+                        if dedupe:
+                            avoid.update(self.query.dupe_avoidance.get(id(opts), lhs_col),
+                                ())
+                            dupe_set.add((opts, lhs_col))
+                        int_opts = int_model._meta
+                        alias = self.query.join(
+                            (alias, int_opts.db_table, lhs_col, int_opts.pk.column),
+                            exclusions=used, promote=True, reuse=used
+                        )
+                        alias_chain.append(alias)
+                        for dupe_opts, dupe_col in dupe_set:
+                            self.query.update_dupe_avoidance(dupe_opts, dupe_col, alias)
+                    dedupe = f.column in opts.duplicate_targets
+                    if dupe_set or dedupe:
+                        avoid.update(self.query.dupe_avoidance.get((id(opts), f.column), ()))
+                        if dedupe:
+                            dupe_set.add((opts, f.column))
+                alias = self.query.join(
+                    (alias, table, f.rel.get_related_field().column, f.column),
+                    exclusions=used.union(avoid),
+                    promote=True
+                )
+                used.add(alias)
+                columns, aliases = self.get_default_columns(start_alias=alias,
+                    opts=model._meta, as_pairs=True)
+                self.query.related_select_cols.extend(columns)
+                self.query.related_select_fields.extend(model._meta.fields)
+
+                next = requested.get(f.related_query_name(), {})
+                new_nullable = f.null or None
+
+                self.fill_related_selections(model._meta, table, cur_depth+1,
+                    used, next, restricted, new_nullable)
+
     def deferred_to_columns(self):
         """
         Converts the self.deferred_loading data structure to mapping of table

docs/ref/models/querysets.txt

@@ -619,17 +619,29 @@ This is also valid::
 
 ...and would also pull in the ``building`` relation.
 
-You can only refer to ``ForeignKey`` relations in the list of fields passed to
+You can refer to any ``ForeignKey`` or ``OneToOneField`` relation in
-``select_related``. You *can* refer to foreign keys that have ``null=True``
+the list of fields passed to ``select_related``. Ths includes foreign
-(unlike the default ``select_related()`` call). It's an error to use both a
+keys that have ``null=True`` (unlike the default ``select_related()``
-list of fields and the ``depth`` parameter in the same ``select_related()``
+call). It's an error to use both a list of fields and the ``depth``
-call, since they are conflicting options.
+parameter in the same ``select_related()`` call, since they are
+conflicting options.
 
 .. versionadded:: 1.0
 
 Both the ``depth`` argument and the ability to specify field names in the call
 to ``select_related()`` are new in Django version 1.0.
 
+.. versionchanged:: 1.2
+
+You can also refer to the reverse direction of a ``OneToOneFields`` in
+the list of fields passed to ``select_related`` -- that is, you can traverse
+a ``OneToOneField`` back to the object on which the field is defined. Instead
+of specifying the field name, use the ``related_name`` for the field on the
+related object.
+
+``OneToOneFields`` will not be traversed in the reverse direction if you
+are performing a depth-based ``select_related``.
+
 .. _queryset-extra:
 
 ``extra(select=None, where=None, params=None, tables=None, order_by=None, select_params=None)``

tests/regressiontests/select_related_onetoone/models.py

@@ -0,0 +1,46 @@
+from django.db import models
+
+
+class User(models.Model):
+    username = models.CharField(max_length=100)
+    email = models.EmailField()
+
+    def __unicode__(self):
+        return self.username
+
+
+class UserProfile(models.Model):
+    user = models.OneToOneField(User)
+    city = models.CharField(max_length=100)
+    state = models.CharField(max_length=2)
+
+    def __unicode__(self):
+        return "%s, %s" % (self.city, self.state)
+
+
+class UserStatResult(models.Model):
+    results = models.CharField(max_length=50)
+
+    def __unicode__(self):
+        return 'UserStatResults, results = %s' % (self.results,)
+
+
+class UserStat(models.Model):
+    user = models.OneToOneField(User, primary_key=True)
+    posts = models.IntegerField()
+    results = models.ForeignKey(UserStatResult)
+
+    def __unicode__(self):
+        return 'UserStat, posts = %s' % (self.posts,)
+
+
+class StatDetails(models.Model):
+    base_stats = models.OneToOneField(UserStat)
+    comments = models.IntegerField()
+
+    def __unicode__(self):
+        return 'StatDetails, comments = %s' % (self.comments,)
+
+
+class AdvancedUserStat(UserStat):
+    pass

tests/regressiontests/select_related_onetoone/tests.py

@@ -0,0 +1,83 @@
+from django import db
+from django.conf import settings
+from django.test import TestCase
+
+from models import User, UserProfile, UserStat, UserStatResult, StatDetails, AdvancedUserStat
+
+class ReverseSelectRelatedTestCase(TestCase):
+    def setUp(self):
+        # Explicitly enable debug for these tests - we need to count
+        # the queries that have been issued.
+        self.old_debug = settings.DEBUG
+        settings.DEBUG = True
+
+        user = User.objects.create(username="test")
+        userprofile = UserProfile.objects.create(user=user, state="KS",
+                                                 city="Lawrence")
+        results = UserStatResult.objects.create(results='first results')
+        userstat = UserStat.objects.create(user=user, posts=150,
+                                           results=results)
+        details = StatDetails.objects.create(base_stats=userstat, comments=259)
+
+        user2 = User.objects.create(username="bob")
+        results2 = UserStatResult.objects.create(results='moar results')
+        advstat = AdvancedUserStat.objects.create(user=user2, posts=200,
+                                                  results=results2)
+        StatDetails.objects.create(base_stats=advstat, comments=250)
+
+        db.reset_queries()
+
+    def assertQueries(self, queries):
+        self.assertEqual(len(db.connection.queries), queries)
+
+    def tearDown(self):
+        settings.DEBUG = self.old_debug
+
+    def test_basic(self):
+        u = User.objects.select_related("userprofile").get(username="test")
+        self.assertEqual(u.userprofile.state, "KS")
+        self.assertQueries(1)
+
+    def test_follow_next_level(self):
+        u = User.objects.select_related("userstat__results").get(username="test")
+        self.assertEqual(u.userstat.posts, 150)
+        self.assertEqual(u.userstat.results.results, 'first results')
+        self.assertQueries(1)
+
+    def test_follow_two(self):
+        u = User.objects.select_related("userprofile", "userstat").get(username="test")
+        self.assertEqual(u.userprofile.state, "KS")
+        self.assertEqual(u.userstat.posts, 150)
+        self.assertQueries(1)
+
+    def test_follow_two_next_level(self):
+        u = User.objects.select_related("userstat__results", "userstat__statdetails").get(username="test")
+        self.assertEqual(u.userstat.results.results, 'first results')
+        self.assertEqual(u.userstat.statdetails.comments, 259)
+        self.assertQueries(1)
+
+    def test_forward_and_back(self):
+        stat = UserStat.objects.select_related("user__userprofile").get(user__username="test")
+        self.assertEqual(stat.user.userprofile.state, 'KS')
+        self.assertEqual(stat.user.userstat.posts, 150)
+        self.assertQueries(1)
+
+    def test_back_and_forward(self):
+        u = User.objects.select_related("userstat").get(username="test")
+        self.assertEqual(u.userstat.user.username, 'test')
+        self.assertQueries(1)
+
+    def test_not_followed_by_default(self):
+        u = User.objects.select_related().get(username="test")
+        self.assertEqual(u.userstat.posts, 150)
+        self.assertQueries(2)
+
+    def test_follow_from_child_class(self):
+        stat = AdvancedUserStat.objects.select_related("statdetails").get(posts=200)
+        self.assertEqual(stat.statdetails.comments, 250)
+        self.assertQueries(1)
+
+    def test_follow_inheritance(self):
+        stat = UserStat.objects.select_related('advanceduserstat').get(posts=200)
+        self.assertEqual(stat.advanceduserstat.posts, 200)
+        self.assertQueries(1)