Fixed #10362 -- An update() that only affects a parent model no longer crashes.

This includes a fairly large refactor of the update() query path (and
the initial portions of constructing the SQL for any query). The
previous code appears to have been only working more or less by accident
and was very fragile.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9967 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -62,6 +62,7 @@ class BaseQuery(object):
         self.dupe_avoidance = {}
         self.used_aliases = set()
         self.filter_is_sticky = False
+        self.included_inherited_models = {}
 
         # SQL-related attributes
         self.select = []
@@ -171,6 +172,7 @@ class BaseQuery(object):
         obj.default_cols = self.default_cols
         obj.default_ordering = self.default_ordering
         obj.standard_ordering = self.standard_ordering
+        obj.included_inherited_models = self.included_inherited_models.copy()
         obj.ordering_aliases = []
         obj.select_fields = self.select_fields[:]
         obj.related_select_fields = self.related_select_fields[:]
@@ -304,6 +306,7 @@ class BaseQuery(object):
             self.select = []
             self.default_cols = False
             self.extra_select = {}
+            self.remove_inherited_models()
 
         query.clear_ordering(True)
         query.clear_limits()
@@ -458,6 +461,7 @@ class BaseQuery(object):
         assert self.distinct == rhs.distinct, \
             "Cannot combine a unique query with a non-unique query."
 
+        self.remove_inherited_models()
         # Work out how to relabel the rhs aliases, if necessary.
         change_map = {}
         used = set()
@@ -540,6 +544,9 @@ class BaseQuery(object):
         """
         if not self.tables:
             self.join((None, self.model._meta.db_table, None, None))
+        if (not self.select and self.default_cols and not
+                self.included_inherited_models):
+            self.setup_inherited_models()
         if self.select_related and not self.related_select_cols:
             self.fill_related_selections()
 
@@ -619,7 +626,9 @@ class BaseQuery(object):
             start_alias=None, opts=None, as_pairs=False):
         """
         Computes the default columns for selecting every field in the base
-        model.
+        model. Will sometimes be called to pull in related models (e.g. via
+        select_related), in which case "opts" and "start_alias" will be given
+        to provide a starting point for the traversal.
 
         Returns a list of strings, quoted appropriately for use in SQL
         directly, as well as a set of aliases used in the select statement (if
@@ -629,22 +638,25 @@ class BaseQuery(object):
         result = []
         if opts is None:
             opts = self.model._meta
-        if start_alias:
-            table_alias = start_alias
-        else:
-            table_alias = self.tables[0]
-        root_pk = opts.pk.column
-        seen = {None: table_alias}
         qn = self.quote_name_unless_alias
         qn2 = self.connection.ops.quote_name
         aliases = set()
+        if start_alias:
+            seen = {None: start_alias}
+            root_pk = opts.pk.column
         for field, model in opts.get_fields_with_model():
+            if start_alias:
                 try:
                     alias = seen[model]
                 except KeyError:
-                alias = self.join((table_alias, model._meta.db_table,
+                    alias = self.join((start_alias, model._meta.db_table,
                             root_pk, model._meta.pk.column))
                     seen[model] = alias
+            else:
+                # If we're starting from the base model of the queryset, the
+                # aliases will have already been set up in pre_sql_setup(), so
+                # we can save time here.
+                alias = self.included_inherited_models[model]
             if as_pairs:
                 result.append((alias, field.column))
                 continue
@@ -996,6 +1008,9 @@ class BaseQuery(object):
                 if alias == old_alias:
                     self.tables[pos] = new_alias
                     break
+        for key, alias in self.included_inherited_models.items():
+            if alias in change_map:
+                self.included_inherited_models[key] = change_map[alias]
 
         # 3. Update any joins that refer to the old alias.
         for alias, data in self.alias_map.iteritems():
@@ -1062,9 +1077,11 @@ class BaseQuery(object):
             lhs.lhs_col = table.col
 
         If 'always_create' is True and 'reuse' is None, a new alias is always
-        created, regardless of whether one already exists or not. Otherwise
+        created, regardless of whether one already exists or not. If
-        'reuse' must be a set and a new join is created unless one of the
+        'always_create' is True and 'reuse' is a set, an alias in 'reuse' that
-        aliases in `reuse` can be used.
+        matches the connection will be returned, if possible.  If
+        'always_create' is False, the first existing alias that matches the
+        'connection' is returned, if any. Otherwise a new join is created.
 
         If 'exclusions' is specified, it is something satisfying the container
         protocol ("foo in exclusions" must work) and specifies a list of
@@ -1126,6 +1143,38 @@ class BaseQuery(object):
         self.rev_join_map[alias] = t_ident
         return alias
 
+    def setup_inherited_models(self):
+        """
+        If the model that is the basis for this QuerySet inherits other models,
+        we need to ensure that those other models have their tables included in
+        the query.
+
+        We do this as a separate step so that subclasses know which
+        tables are going to be active in the query, without needing to compute
+        all the select columns (this method is called from pre_sql_setup(),
+        whereas column determination is a later part, and side-effect, of
+        as_sql()).
+        """
+        opts = self.model._meta
+        root_pk = opts.pk.column
+        root_alias = self.tables[0]
+        seen = {None: root_alias}
+        for field, model in opts.get_fields_with_model():
+            if model not in seen:
+                seen[model] = self.join((root_alias, model._meta.db_table,
+                        root_pk, model._meta.pk.column))
+        self.included_inherited_models = seen
+
+    def remove_inherited_models(self):
+        """
+        Undoes the effects of setup_inherited_models(). Should be called
+        whenever select columns (self.select) are set explicitly.
+        """
+        for key, alias in self.included_inherited_models.items():
+            if key:
+                self.unref_alias(alias)
+        self.included_inherited_models = {}
+
     def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
             used=None, requested=None, restricted=None, nullable=None,
             dupe_set=None, avoid_set=None):
@@ -1803,6 +1852,7 @@ class BaseQuery(object):
             names.sort()
             raise FieldError("Cannot resolve keyword %r into field. "
                     "Choices are: %s" % (name, ", ".join(names)))
+        self.remove_inherited_models()
 
     def add_ordering(self, *ordering):
         """
@@ -2004,6 +2054,7 @@ class BaseQuery(object):
             select_alias = join_info[RHS_ALIAS]
             select_col = join_info[RHS_JOIN_COL]
         self.select = [(select_alias, select_col)]
+        self.remove_inherited_models()
 
     def execute_sql(self, result_type=MULTI):
         """

django/db/models/sql/subqueries.py

@@ -179,21 +179,9 @@ class UpdateQuery(Query):
         query = self.clone(klass=Query)
         query.bump_prefix()
         query.extra_select = {}
-        first_table = query.tables[0]
-        if query.alias_refcount[first_table] == 1:
-            # We can remove one table from the inner query.
-            query.unref_alias(first_table)
-            for i in xrange(1, len(query.tables)):
-                table = query.tables[i]
-                if query.alias_refcount[table]:
-                    break
-            join_info = query.alias_map[table]
-            query.select = [(join_info[RHS_ALIAS], join_info[RHS_JOIN_COL])]
-            must_pre_select = False
-        else:
         query.select = []
         query.add_fields([query.model._meta.pk.name])
-            must_pre_select = not self.connection.features.update_can_self_select
+        must_pre_select = count > 1 and not self.connection.features.update_can_self_select
 
         # Now we adjust the current query: reset the where clause and get rid
         # of all the tables we don't need (since they're in the sub-select).

tests/regressiontests/model_inheritance_regress/models.py

@@ -222,7 +222,7 @@ True
 >>> obj = SelfRefChild.objects.create(child_data=37, parent_data=42)
 >>> obj.delete()
 
-# Regression tests for #8076 - get_(next/previous)_by_date should 
+# Regression tests for #8076 - get_(next/previous)_by_date should work.
 >>> c1 = ArticleWithAuthor(headline='ArticleWithAuthor 1', author="Person 1", pub_date=datetime.datetime(2005, 8, 1, 3, 0))
 >>> c1.save()
 >>> c2 = ArticleWithAuthor(headline='ArticleWithAuthor 2', author="Person 2", pub_date=datetime.datetime(2005, 8, 1, 10, 0))
@@ -267,4 +267,12 @@ DoesNotExist: ArticleWithAuthor matching query does not exist.
 >>> fragment.find('pub_date', pos + 1) == -1
 True
 
+# It is possible to call update() and only change a field in an ancestor model
+# (regression test for #10362).
+>>> article = ArticleWithAuthor.objects.create(author="fred", headline="Hey there!", pub_date = datetime.datetime(2009, 3, 1, 8, 0, 0))
+>>> ArticleWithAuthor.objects.filter(author="fred").update(headline="Oh, no!")
+1
+>>> ArticleWithAuthor.objects.filter(pk=article.pk).update(headline="Oh, no!")
+1
+
 """}