Changeset 2485

Timestamp:

03/03/06 18:19:59 (3 years ago)

Author:

lukeplant

Message:

magic-removal: Implemented 'laziness' for QuerySet? slicing, to restore functionality that was previously possible with generic views via 'limit' and 'extra_lookup_args'

Files:

• django/branches/magic-removal/django/db/models/query.py (modified) (9 diffs)
• django/branches/magic-removal/tests/modeltests/basic/models.py (modified) (1 diff)

django/branches/magic-removal/django/db/models/query.py

@@ -96 +96 @@
-    def __getitem__(self, k):
-        "Retrieve an item or slice from the set of results."
-        # __getitem__ can't return QuerySet instances, because filter() and
-        # order_by() on the result would break badly. This means we don't have
-        # to worry about arithmetic with self._limit or self._offset -- they'll
-        # both be None at this point.
-        if self._result_cache is None:
-            if isinstance(k, slice):
+                # Offset:
+                if self._offset is None:
+                    offset = k.start
+                elif k.start is None:
+                    offset = self._offset
+                else:
+                    offset = self._offset + k.start
+                # Now adjust offset to the bounds of any existing limit:
+                if self._limit is not None and k.start is not None:
+                    limit = self._limit - k.start
+                else:
+                    limit = self._limit
+
+                # Limit:
-                if k.stop is not None and k.start is not None:
-
+
+
+
+
-                else:
-
-
+
+
+
+
+
+
+
+
+
+
-            else:
-                return self._clone(_offset=k, _limit=1).get()
@@ -180 +201 @@
-        latest_by = field_name or self.model._meta.get_latest_by
-        assert bool(latest_by), "latest() requires either a field_name parameter or 'get_latest_by' in the model"
+        assert self._limit is None and self._offset is None, \
+                "Cannot change a query once a slice has been taken."
-        return self._clone(_limit=1, _order_by=('-'+latest_by,)).get()
-
@@ -187 +210 @@
-        that ID.
-        """
+        assert self._limit is None and self._offset is None, \
+                "Cannot use 'limit' or 'offset' with in_bulk"
-        assert isinstance(id_list, (tuple,  list)), "in_bulk() must be provided with a list of IDs."
-        id_list = list(id_list)
@@ -199 +224 @@
-        Deletes the records in the current QuerySet.
-        """
+        assert self._limit is None and self._offset is None, \
+            "Cannot use 'limit' or 'offset' with delete."
+
-        del_query = self._clone()
-
@@ -204 +232 @@
-        del_query._select_related = False
-        del_query._order_by = []
-        del_query._offset = None
-        del_query._limit = None
-
-        # Collect all the objects to be deleted, and all the objects that are related to
@@ -252 +278 @@
-        
-    def _filter_or_exclude(self, qtype, *args, **kwargs):
+        if len(args) > 0 or len(kwargs) > 0:
+            assert self._limit is None and self._offset is None, \
+                "Cannot filter a query once a slice has been taken."
+
-        clone = self._clone()
-        if len(kwargs) > 0:
@@ -265 +295 @@
-    def order_by(self, *field_names):
-        "Returns a new QuerySet instance with the ordering changed."
+        assert self._limit is None and self._offset is None, \
+                "Cannot reorder a query once a slice has been taken."
-        return self._clone(_order_by=field_names)
-
@@ -272 +304 @@
-
-    def extra(self, select=None, where=None, params=None, tables=None):
+        assert self._limit is None and self._offset is None, \
+                "Cannot change a query once a slice has been taken"
-        clone = self._clone()
-        if select: clone._select.extend(select)
@@ -302 +336 @@
-
-    def _combine(self, other):
-
-
+
+
+
+
+
-        #  use 'other's order by
-        #  (so that A.filter(args1) & A.filter(args2) does the same as

django/branches/magic-removal/tests/modeltests/basic/models.py

@@ -240 +240 @@
-[Area woman programs in Python, Third article]
-
+# Slices (without step) are lazy:
+>>> Article.objects.all()[0:5].filter()
+[Area woman programs in Python, Second article, Third article, Fourth article, Article 6]
+
+# Slicing again works:
+>>> Article.objects.all()[0:5][0:2]
+[Area woman programs in Python, Second article]
+>>> Article.objects.all()[0:5][:2]
+[Area woman programs in Python, Second article]
+>>> Article.objects.all()[0:5][4:]
+[Article 6]
+>>> Article.objects.all()[0:5][5:]
+[]
+
+# Some more tests!
+>>> Article.objects.all()[2:][0:2]
+[Third article, Fourth article]
+>>> Article.objects.all()[2:][:2]
+[Third article, Fourth article]
+>>> Article.objects.all()[2:][2:3]
+[Article 6]
+
+# Note that you can't use 'offset' without 'limit' (on some dbs), so this doesn't work:
+>>> Article.objects.all()[2:]
+Traceback (most recent call last):
+    ...
+AssertionError: 'offset' is not allowed without 'limit'
+
+# Also, once you have sliced you can't filter, re-order or combine
+>>> Article.objects.all()[0:5].filter(id=1)
+Traceback (most recent call last):
+    ...
+AssertionError: Cannot filter a query once a slice has been taken.
+
+>>> Article.objects.all()[0:5].order_by('id')
+Traceback (most recent call last):
+    ...
+AssertionError: Cannot reorder a query once a slice has been taken.
+
+>>> Article.objects.all()[0:1] & Article.objects.all()[4:5]
+Traceback (most recent call last):
+    ...
+AssertionError: Cannot combine queries once a slice has been taken.
+
+
-# An Article instance doesn't have access to the "objects" attribute.
-# That's only available on the class.