diff options
Diffstat (limited to 'django/db/models/sql')
| -rw-r--r-- | django/db/models/sql/expressions.py | 2 | ||||
| -rw-r--r-- | django/db/models/sql/query.py | 53 |
2 files changed, 35 insertions, 20 deletions
diff --git a/django/db/models/sql/expressions.py b/django/db/models/sql/expressions.py index f011db2165..920cbffe73 100644 --- a/django/db/models/sql/expressions.py +++ b/django/db/models/sql/expressions.py @@ -42,7 +42,7 @@ class SQLEvaluator(object): field, source, opts, join_list, last, _ = query.setup_joins( field_list, query.get_meta(), query.get_initial_alias(), False) - _, _, col, _, join_list = query.trim_joins(source, join_list, last, False) + col, _, join_list = query.trim_joins(source, join_list, last, False) self.cols[node] = (join_list[-1], col) except FieldDoesNotExist: diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py index fb07529ee2..7c2816f715 100644 --- a/django/db/models/sql/query.py +++ b/django/db/models/sql/query.py @@ -1287,7 +1287,7 @@ class BaseQuery(object): field_list, opts, self.get_initial_alias(), False) # Process the join chain to see if it can be trimmed - _, _, col, _, join_list = self.trim_joins(source, join_list, last, False) + col, _, join_list = self.trim_joins(source, join_list, last, False) # If the aggregate references a model or field that requires a join, # those joins must be LEFT OUTER - empty join rows must be returned @@ -1392,16 +1392,16 @@ class BaseQuery(object): can_reuse) return - # Process the join chain to see if it can be trimmed - final, penultimate, col, alias, join_list = self.trim_joins(target, join_list, last, trim) - if (lookup_type == 'isnull' and value is True and not negate and - final > 1): - # If the comparison is against NULL, we need to use a left outer - # join when connecting to the previous model. We make that - # adjustment here. We don't do this unless needed as it's less - # efficient at the database level. - self.promote_alias(join_list[penultimate]) + len(join_list) > 1): + # If the comparison is against NULL, we may need to use some left + # outer joins when creating the join chain. This is only done when + # needed, as it's less efficient at the database level. + self.promote_alias_chain(join_list) + + # Process the join list to see if we can remove any inner joins from + # the far end (fewer tables in a query is better). + col, alias, join_list = self.trim_joins(target, join_list, last, trim) if connector == OR: # Some joins may need to be promoted when adding a new filter to a @@ -1436,7 +1436,7 @@ class BaseQuery(object): if negate: self.promote_alias_chain(join_list) if lookup_type != 'isnull': - if final > 1: + if len(join_list) > 1: for alias in join_list: if self.alias_map[alias][JOIN_TYPE] == self.LOUTER: j_col = self.alias_map[alias][RHS_JOIN_COL] @@ -1699,13 +1699,28 @@ class BaseQuery(object): return field, target, opts, joins, last, extra_filters def trim_joins(self, target, join_list, last, trim): - """An optimization: if the final join is against the same column as - we are comparing against, we can go back one step in a join - chain and compare against the LHS of the join instead (and then - repeat the optimization). The result, potentially, involves less - table joins. + """ + Sometimes joins at the end of a multi-table sequence can be trimmed. If + the final join is against the same column as we are comparing against, + and is an inner join, we can go back one step in a join chain and + compare against the LHS of the join instead (and then repeat the + optimization). The result, potentially, involves less table joins. + + The 'target' parameter is the final field being joined to, 'join_list' + is the full list of join aliases. + + The 'last' list contains offsets into 'join_list', corresponding to + each component of the filter. Many-to-many relations, for example, add + two tables to the join list and we want to deal with both tables the + same way, so 'last' has an entry for the first of the two tables and + then the table immediately after the second table, in that case. + + The 'trim' parameter forces the final piece of the join list to be + trimmed before anything. See the documentation of add_filter() for + details about this. - Returns a tuple + Returns the final active column and table alias and the new active + join_list. """ final = len(join_list) penultimate = last.pop() @@ -1724,7 +1739,7 @@ class BaseQuery(object): alias = join_list[-1] while final > 1: join = self.alias_map[alias] - if col != join[RHS_JOIN_COL]: + if col != join[RHS_JOIN_COL] or join[JOIN_TYPE] != self.INNER: break self.unref_alias(alias) alias = join[LHS_ALIAS] @@ -1733,7 +1748,7 @@ class BaseQuery(object): final -= 1 if final == penultimate: penultimate = last.pop() - return final, penultimate, col, alias, join_list + return col, alias, join_list def update_dupe_avoidance(self, opts, col, alias): """ |