Removed dupe_avoidance from sql/query and sql/compiler.py

The dupe avoidance logic was removed as it doesn't seem to do anything, it is complicated, and it has nearly zero documentation. The removal of dupe_avoidance allowed for refactoring of both the implementation and signature of Query.join(). This refactoring cascades again to some other parts. The most significant of them is the changes in qs.combine(), and compiler.select_related_descent().

Author: akaariai

django/db/models/fields/related.py

@@ -1053,11 +1053,6 @@ def value_to_string(self, obj):
  def contribute_to_class(self, cls, name):
  super(ForeignKey, self).contribute_to_class(cls, name)
  setattr(cls, self.name, ReverseSingleRelatedObjectDescriptor(self))
- if isinstance(self.rel.to, six.string_types):
- target = self.rel.to
- else:
- target = self.rel.to._meta.db_table
- cls._meta.duplicate_targets[self.column] = (target, "o2m")
 
  def contribute_to_related_class(self, cls, related):
  # Internal FK's - i.e., those with a related name ending with '+' -
@@ -1293,12 +1288,6 @@ def resolve_through_model(field, model, cls):
  field.rel.through = model
  add_lazy_relation(cls, self, self.rel.through, resolve_through_model)
 
- if isinstance(self.rel.to, six.string_types):
- target = self.rel.to
- else:
- target = self.rel.to._meta.db_table
- cls._meta.duplicate_targets[self.column] = (target, "m2m")
-
  def contribute_to_related_class(self, cls, related):
  # Internal M2Ms (i.e., those with a related name ending with '+')
  # and swapped models don't get a related descriptor.

django/db/models/options.py

@@ -58,7 +58,6 @@ def __init__(self, meta, app_label=None):
  self.concrete_model = None
  self.swappable = None
  self.parents = SortedDict()
- self.duplicate_targets = {}
  self.auto_created = False
 
  # To handle various inheritance situations, we need to track where
@@ -147,24 +146,6 @@ def _prepare(self, model):
  auto_created=True)
  model.add_to_class('id', auto)
 
- # Determine any sets of fields that are pointing to the same targets
- # (e.g. two ForeignKeys to the same remote model). The query
- # construction code needs to know this. At the end of this,
- # self.duplicate_targets will map each duplicate field column to the
- # columns it duplicates.
- collections = {}
- for column, target in six.iteritems(self.duplicate_targets):
- try:
- collections[target].add(column)
- except KeyError:
- collections[target] = set([column])
- self.duplicate_targets = {}
- for elt in six.itervalues(collections):
- if len(elt) == 1:
- continue
- for column in elt:
- self.duplicate_targets[column] = elt.difference(set([column]))
-
  def add_field(self, field):
  # Insert the given field in the order in which it was created, using
  # the "creation_counter" attribute of the field.

django/db/models/sql/compiler.py

@@ -6,7 +6,7 @@
 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, SelectInfo)
+ GET_ITERATOR_CHUNK_SIZE, REUSE_ALL, 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
@@ -457,7 +457,7 @@ def _setup_joins(self, pieces, opts, alias):
  if not alias:
  alias = self.query.get_initial_alias()
  field, target, opts, joins, _, _ = self.query.setup_joins(pieces,
- opts, alias, False)
+ opts, alias, REUSE_ALL)
  # 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]
@@ -574,8 +574,7 @@ def get_grouping(self):
  return result, params
 
  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):
+ requested=None, restricted=None, nullable=None):
  """
  Fill in the information needed for a select_related query. The current
  depth is measured as the number of connections away from the root model
@@ -590,13 +589,6 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  opts = self.query.get_meta()
  root_alias = self.query.get_initial_alias()
  self.query.related_select_cols = []
- if not used:
- used = set()
- if dupe_set is None:
- dupe_set = set()
- if avoid_set is None:
- avoid_set = set()
- orig_dupe_set = dupe_set
  only_load = self.query.get_loaded_field_names()
 
  # Setup for the case when only particular related fields should be
@@ -616,12 +608,6 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  if not select_related_descend(f, restricted, requested,
  only_load.get(field_model)):
  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 = f.rel.to._meta.db_table
  promote = nullable or f.null
  if model:
@@ -637,31 +623,17 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  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,
+ int_opts.pk.column),
  promote=promote)
  alias_chain.append(alias)
- for (dupe_opts, dupe_col) in dupe_set:
- self.query.update_dupe_avoidance(dupe_opts, dupe_col, alias)
  else:
  alias = root_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.column,
  f.rel.get_related_field().column),
- exclusions=used.union(avoid), promote=promote)
- used.add(alias)
+ promote=promote)
  columns, aliases = self.get_default_columns(start_alias=alias,
  opts=f.rel.to._meta, as_pairs=True)
  self.query.related_select_cols.extend(
@@ -671,10 +643,8 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  else:
  next = False
  new_nullable = f.null or promote
- for dupe_opts, dupe_col in dupe_set:
- self.query.update_dupe_avoidance(dupe_opts, dupe_col, alias)
  self.fill_related_selections(f.rel.to._meta, alias, cur_depth + 1,
- used, next, restricted, new_nullable, dupe_set, avoid)
+ next, restricted, new_nullable)
 
  if restricted:
  related_fields = [
@@ -686,14 +656,8 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  if not select_related_descend(f, restricted, requested,
  only_load.get(model), 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
 
+ table = model._meta.db_table
  int_opts = opts
  alias = root_alias
  alias_chain = []
@@ -708,30 +672,16 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  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
+ promote=True,
  )
  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, local_only=True)
  self.query.related_select_cols.extend(
@@ -743,7 +693,7 @@ def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
  new_nullable = True
 
  self.fill_related_selections(model._meta, table, cur_depth+1,
- used, next, restricted, new_nullable)
+ next, restricted, new_nullable)
 
  def deferred_to_columns(self):
  """

django/db/models/sql/constants.py

@@ -37,3 +37,6 @@
  'ASC': ('ASC', 'DESC'),
  'DESC': ('DESC', 'ASC'),
 }
+
+# A marker for join-reusability.
+REUSE_ALL = object()