Commit 90b86291 authored by Anssi Kääriäinen's avatar Anssi Kääriäinen
Browse files

Fixed #18375 -- Removed dict-ordering dependency for F-expressions 

F() expressions reuse joins like any lookup in a .filter() call -
reuse multijoins generated in the same .filter() call else generate
new joins. Also, lookups can now reuse joins generated by F().

This change is backwards incompatible, but it is required to prevent
dict randomization from generating different queries depending on
.filter() kwarg ordering. The new way is also more consistent in how
joins are reused.
parent 7b9a1fb9

django/db/models/sql/expressions.py

+6 −3
Original line number Diff line number Diff line 
from django.core.exceptions import FieldError

from django.db.models.constants import LOOKUP_SEP

from django.db.models.fields import FieldDoesNotExist

from django.db.models.sql.constants import REUSE_ALL



class SQLEvaluator(object):

    def __init__(self, expression, query, allow_joins=True):

    def __init__(self, expression, query, allow_joins=True, reuse=REUSE_ALL):

        self.expression = expression

        self.opts = query.get_meta()

        self.cols = []



        self.contains_aggregate = False

        self.reuse = reuse

        self.expression.prepare(self, query, allow_joins)



    def prepare(self):
@@ -50,9 +52,10 @@ class SQLEvaluator(object): 
            try:

                field, source, opts, join_list, last, _ = query.setup_joins(

                    field_list, query.get_meta(),

                    query.get_initial_alias(), False)

                    query.get_initial_alias(), self.reuse)

                col, _, join_list = query.trim_joins(source, join_list, last, False)



                if self.reuse is not None and self.reuse != REUSE_ALL:

                    self.reuse.update(join_list)

                self.cols.append((node, (join_list[-1], col)))

            except FieldDoesNotExist:

                raise FieldError("Cannot resolve keyword %r into field. "

django/db/models/sql/query.py

+1 −1
Original line number Diff line number Diff line
@@ -1096,7 +1096,7 @@ class Query(object): 
            value = value()

        elif isinstance(value, ExpressionNode):

            # If value is a query expression, evaluate it

            value = SQLEvaluator(value, self)

            value = SQLEvaluator(value, self, reuse=can_reuse)

            having_clause = value.contains_aggregate



        for alias, aggregate in self.aggregates.items():

docs/releases/1.5.txt

+6 −0
Original line number Diff line number Diff line
@@ -589,6 +589,12 @@ Miscellaneous 
  :ref:`Q() expressions <complex-lookups-with-q>` and ``QuerySet`` combining where

  the operators are used as boolean AND and OR operators.



* In a ``filter()`` call, when :ref:`F() expressions <query-expressions>`

  contained lookups spanning multi-valued relations, they didn't always reuse

  the same relations as other lookups along the same chain. This was changed,

  and now F() expressions will always use the same relations as other lookups

  within the same ``filter()`` call.



* The :ttag:`csrf_token` template tag is no longer enclosed in a div. If you need

  HTML validation against pre-HTML5 Strict DTDs, you should add a div around it

  in your pages.

tests/modeltests/expressions/tests.py

+39 −0
Original line number Diff line number Diff line
@@ -219,3 +219,42 @@ class ExpressionsTests(TestCase): 
        )

        acme.num_employees = F("num_employees") + 16

        self.assertRaises(TypeError, acme.save)



    def test_ticket_18375_join_reuse(self):

        # Test that reverse multijoin F() references and the lookup target

        # the same join. Pre #18375 the F() join was generated first, and the

        # lookup couldn't reuse that join.

        qs = Employee.objects.filter(

            company_ceo_set__num_chairs=F('company_ceo_set__num_employees'))

        self.assertEqual(str(qs.query).count('JOIN'), 1)



    def test_ticket_18375_kwarg_ordering(self):

        # The next query was dict-randomization dependent - if the "gte=1"

        # was seen first, then the F() will reuse the join generated by the

        # gte lookup, if F() was seen first, then it generated a join the

        # other lookups could not reuse.

        qs = Employee.objects.filter(

            company_ceo_set__num_chairs=F('company_ceo_set__num_employees'),

            company_ceo_set__num_chairs__gte=1)

        self.assertEqual(str(qs.query).count('JOIN'), 1)



    def test_ticket_18375_kwarg_ordering_2(self):

        # Another similar case for F() than above. Now we have the same join

        # in two filter kwargs, one in the lhs lookup, one in F. Here pre

        # #18375 the amount of joins generated was random if dict

        # randomization was enabled, that is the generated query dependend

        # on which clause was seen first.

        qs = Employee.objects.filter(

            company_ceo_set__num_employees=F('pk'),

            pk=F('company_ceo_set__num_employees')

        )

        self.assertEqual(str(qs.query).count('JOIN'), 1)



    def test_ticket_18375_chained_filters(self):

        # Test that F() expressions do not reuse joins from previous filter.

        qs = Employee.objects.filter(

            company_ceo_set__num_employees=F('pk')

        ).filter(

            company_ceo_set__num_employees=F('company_ceo_set__num_employees')

        )

        self.assertEqual(str(qs.query).count('JOIN'), 2)