Fixed #19500 -- Solved a regression in join reuse

The ORM didn't reuse joins for direct foreign key traversals when using
chained filters. For example:
    qs.filter(fk__somefield=1).filter(fk__somefield=2))
produced two joins.

As a bonus, reverse onetoone filters can now reuse joins correctly

The regression was caused by the join() method refactor in commit
68847135bc9acb2c51c2d36797d0a85395f0cd35

Thanks for Simon Charette for spotting some issues with the first draft
of the patch.

1 files changed, 4 insertions, 4 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index 4d846fb438..4a12d74452 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -6,7 +6,7 @@ from django.db.backends.util import truncate_name
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.query_utils import select_related_descend
 from django.db.models.sql.constants import (SINGLE, MULTI, ORDER_DIR,
-        GET_ITERATOR_CHUNK_SIZE, REUSE_ALL, SelectInfo)
+        GET_ITERATOR_CHUNK_SIZE, SelectInfo)
 from django.db.models.sql.datastructures import EmptyResultSet
 from django.db.models.sql.expressions import SQLEvaluator
 from django.db.models.sql.query import get_order_dir, Query
@@ -317,7 +317,7 @@ class SQLCompiler(object):
 
         for name in self.query.distinct_fields:
             parts = name.split(LOOKUP_SEP)
-            field, col, alias, _, _ = self._setup_joins(parts, opts, None)
+            field, col, alias, _, _ = self._setup_joins(parts, opts)
             col, alias = self._final_join_removal(col, alias)
             result.append("%s.%s" % (qn(alias), qn2(col)))
         return result
@@ -450,7 +450,7 @@ class SQLCompiler(object):
         if not alias:
             alias = self.query.get_initial_alias()
         field, target, opts, joins, _ = self.query.setup_joins(
-            pieces, opts, alias, REUSE_ALL)
+            pieces, opts, alias)
         # We will later on need to promote those joins that were added to the
         # query afresh above.
         joins_to_promote = [j for j in joins if self.query.alias_refcount[j] < 2]
@@ -688,7 +688,7 @@ class SQLCompiler(object):
                         int_opts = int_model._meta
                         alias = self.query.join(
                             (alias, int_opts.db_table, lhs_col, int_opts.pk.column),
-                            promote=True,
+                            promote=True
                         )
                         alias_chain.append(alias)
                 alias = self.query.join(