magic-removal: Fixed #1136: Removed duplicated DB joins resulting fro…

…m kwarg evaluation. Thanks, Russ Magee

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@1792 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/manager.py

@@ -33,7 +33,7 @@ def __init__(self):
         self.creation_counter = Manager.creation_counter
         Manager.creation_counter += 1
         self.klass = None
-    
+
     def _prepare(self):
         if self.klass._meta.get_latest_by:
             self.get_latest = self.__get_latest
@@ -49,7 +49,7 @@ def contribute_to_class(self, klass, name):
         if not hasattr(klass, '_default_manager') or \
            self.creation_counter < klass._default_manager.creation_counter:
                 klass._default_manager = self
-        
+
     def _get_sql_clause(self, **kwargs):
         def quote_only_if_word(word):
             if ' ' in word:
@@ -61,15 +61,14 @@ def quote_only_if_word(word):
 
         # Construct the fundamental parts of the query: SELECT X FROM Y WHERE Z.
         select = ["%s.%s" % (backend.quote_name(opts.db_table), backend.quote_name(f.column)) for f in opts.fields]
-        tables = [opts.db_table] + (kwargs.get('tables') and kwargs['tables'][:] or [])
-        tables = [quote_only_if_word(t) for t in tables]
+        tables = (kwargs.get('tables') and [quote_only_if_word(t) for t in kwargs['tables']] or [])
         where = kwargs.get('where') and kwargs['where'][:] or []
         params = kwargs.get('params') and kwargs['params'][:] or []
 
         # Convert the kwargs into SQL.
-        tables2, join_where2, where2, params2, _ = parse_lookup(kwargs.items(), opts)
+        tables2, joins, where2, params2 = parse_lookup(kwargs.items(), opts)
         tables.extend(tables2)
-        where.extend(join_where2 + where2)
+        where.extend(where2)
         params.extend(params2)
 
         # Add any additional constraints from the "where_constraints" parameter.
@@ -83,6 +82,22 @@ def quote_only_if_word(word):
         if kwargs.get('select'):
             select.extend(['(%s) AS %s' % (quote_only_if_word(s[1]), backend.quote_name(s[0])) for s in kwargs['select']])
 
+        # Start composing the body of the SQL statement.
+        sql = [" FROM", backend.quote_name(opts.db_table)]
+
+        # Compose the join dictionary into SQL describing the joins.
+        if joins:
+            sql.append(" ".join(["%s %s AS %s ON %s" % (join_type, table, alias, condition)
+                                for (alias, (table, join_type, condition)) in joins.items()]))
+
+        # Compose the tables clause into SQL.
+        if tables:
+            sql.append(", " + ", ".join(tables))
+
+        # Compose the where clause into SQL.
+        if where:
+            sql.append(where and "WHERE " + " AND ".join(where))
+
         # ORDER BY clause
         order_by = []
         for f in handle_legacy_orderlist(kwargs.get('order_by', opts.ordering)):
@@ -106,16 +121,16 @@ def quote_only_if_word(word):
                     else:
                         table_prefix = ''
                 order_by.append('%s%s %s' % (table_prefix, backend.quote_name(orderfield2column(col_name, opts)), order))
-        order_by = ", ".join(order_by)
+        if order_by:
+            sql.append("ORDER BY " + ", ".join(order_by))
 
         # LIMIT and OFFSET clauses
         if kwargs.get('limit') is not None:
-            limit_sql = " %s " % backend.get_limit_offset_sql(kwargs['limit'], kwargs.get('offset'))
+            sql.append("%s " % backend.get_limit_offset_sql(kwargs['limit'], kwargs.get('offset')))
         else:
             assert kwargs.get('offset') is None, "'offset' is not allowed without 'limit'"
-            limit_sql = ""
 
-        return select, " FROM " + ",".join(tables) + (where and " WHERE " + " AND ".join(where) or "") + (order_by and " ORDER BY " + order_by or "") + limit_sql, params
+        return select, " ".join(sql), params
 
     def get_iterator(self, **kwargs):
         # kwargs['select'] is a dictionary, and dictionaries' key order is
@@ -220,7 +235,7 @@ def __get_date_list(self, field, *args, **kwargs):
         # We have to manually run typecast_timestamp(str()) on the results, because
         # MySQL doesn't automatically cast the result of date functions as datetime
         # objects -- MySQL returns the values as strings, instead.
-        return [typecast_timestamp(str(row[0])) for row in cursor.fetchall()] 
+        return [typecast_timestamp(str(row[0])) for row in cursor.fetchall()]
 
 class ManagerDescriptor(object):
     def __init__(self, manager):

django/db/models/query.py

@@ -45,25 +45,25 @@ def orderlist2sql(order_list, opts, prefix=''):
             output.append('%s%s ASC' % (prefix, backend.quote_name(orderfield2column(f, opts))))
     return ', '.join(output)
 
-class QBase:
+class QOperator:
     "Base class for QAnd and QOr"
     def __init__(self, *args):
         self.args = args
 
     def __repr__(self):
         return '(%s)' % self.operator.join([repr(el) for el in self.args])
 
-    def get_sql(self, opts, table_count):
-        tables, join_where, where, params = [], [], [], []
+    def get_sql(self, opts):
+        tables, joins, where, params = [], {}, [], []
         for val in self.args:
-            tables2, join_where2, where2, params2, table_count = val.get_sql(opts, table_count)
+            tables2, joins2, where2, params2 = val.get_sql(opts)
             tables.extend(tables2)
-            join_where.extend(join_where2)
+            joins.update(joins2)
             where.extend(where2)
             params.extend(params2)
-        return tables, join_where, ['(%s)' % self.operator.join(where)], params, table_count
+        return tables, joins, ['(%s)' % self.operator.join(where)], params
 
-class QAnd(QBase):
+class QAnd(QOperator):
     "Encapsulates a combined query that uses 'AND'."
     operator = ' AND '
     def __or__(self, other):
@@ -80,7 +80,7 @@ def __and__(self, other):
         else:
             raise TypeError, other
 
-class QOr(QBase):
+class QOr(QOperator):
     "Encapsulates a combined query that uses 'OR'."
     operator = ' OR '
     def __and__(self, other):
@@ -117,8 +117,8 @@ def __or__(self, other):
         else:
             raise TypeError, other
 
-    def get_sql(self, opts, table_count):
-        return parse_lookup(self.kwargs.items(), opts, table_count)
+    def get_sql(self, opts):
+        return parse_lookup(self.kwargs.items(), opts)
 
 
 def get_where_clause(lookup_type, table_prefix, field_name, value):
@@ -174,33 +174,40 @@ def throw_bad_kwarg_error(kwarg):
     # Helper function to remove redundancy.
     raise TypeError, "got unexpected keyword argument '%s'" % kwarg
 
-def parse_lookup(kwarg_items, opts, table_count=0):
+def parse_lookup(kwarg_items, opts):
     # Helper function that handles converting API kwargs (e.g.
     # "name__exact": "tom") to SQL.
 
-    # Note that there is a distinction between where and join_where. The latter
-    # is specifically a list of where clauses to use for JOINs. This
-    # distinction is necessary because of support for "_or".
-
-    # table_count is used to ensure table aliases are unique.
-    tables, join_where, where, params = [], [], [], []
+    # 'joins' is a dictionary describing the tables that must be joined to complete the query.
+    # Each key-value pair follows the form
+    #   alias: (table, join_type, condition)
+    # where
+    #   alias is the AS alias for the joined table
+    #   table is the actual table name to be joined
+    #   join_type is the type of join (INNER JOIN, LEFT OUTER JOIN, etc)
+    #   condition is the where-like statement over which narrows the join.
+    #
+    # alias will be derived from the lookup list name.
+    # At present, this method only every returns INNER JOINs; the option is there for others
+    # to implement custom Q()s, etc that return other join types.
+    tables, joins, where, params = [], {}, [], []
     for kwarg, kwarg_value in kwarg_items:
         if kwarg in ('order_by', 'limit', 'offset', 'select_related', 'distinct', 'select', 'tables', 'where', 'params'):
             continue
         if kwarg_value is None:
             continue
         if kwarg == 'complex':
-            tables2, join_where2, where2, params2, table_count = kwarg_value.get_sql(opts, table_count)
+            tables2, joins2, where2, params2 = kwarg_value.get_sql(opts)
             tables.extend(tables2)
-            join_where.extend(join_where2)
+            joins.update(joins2)
             where.extend(where2)
             params.extend(params2)
             continue
         if kwarg == '_or':
             for val in kwarg_value:
-                tables2, join_where2, where2, params2, table_count = parse_lookup(val, opts, table_count)
+                tables2, joins2, where2, params2 = parse_lookup(val, opts)
                 tables.extend(tables2)
-                join_where.extend(join_where2)
+                joins.update(joins2)
                 where.append('(%s)' % ' OR '.join(where2))
                 params.extend(params2)
             continue
@@ -212,17 +219,16 @@ def parse_lookup(kwarg_items, opts, table_count=0):
             else:
                 lookup_list = lookup_list[:-1] + [opts.pk.name, 'exact']
         if len(lookup_list) == 1:
-            _throw_bad_kwarg_error(kwarg)
+            throw_bad_kwarg_error(kwarg)
         lookup_type = lookup_list.pop()
         current_opts = opts # We'll be overwriting this, so keep a reference to the original opts.
         current_table_alias = current_opts.db_table
         param_required = False
         while lookup_list or param_required:
-            table_count += 1
             try:
                 # "current" is a piece of the lookup list. For example, in
                 # choices.get_list(poll__sites__id__exact=5), lookup_list is
-                # ["polls", "sites", "id"], and the first current is "polls".
+                # ["poll", "sites", "id"], and the first current is "poll".
                 try:
                     current = lookup_list.pop(0)
                 except IndexError:
@@ -233,15 +239,18 @@ def parse_lookup(kwarg_items, opts, table_count=0):
                 # Try many-to-many relationships first...
                 for f in current_opts.many_to_many:
                     if f.name == current:
-                        rel_table_alias = backend.quote_name('t%s' % table_count)
-                        table_count += 1
-                        tables.append('%s %s' % \
-                            (backend.quote_name(f.get_m2m_db_table(current_opts)), rel_table_alias))
-                        join_where.append('%s.%s = %s.%s' % \
-                            (backend.quote_name(current_table_alias),
-                            backend.quote_name(current_opts.pk.column),
-                            rel_table_alias,
-                            backend.quote_name(current_opts.object_name.lower() + '_id')))
+                        rel_table_alias = backend.quote_name(current_table_alias + LOOKUP_SEPARATOR + current)
+
+                        joins[rel_table_alias] = (
+                            backend.quote_name(f.get_m2m_db_table(current_opts)),
+                            "INNER JOIN",
+                            '%s.%s = %s.%s' %
+                                (backend.quote_name(current_table_alias),
+                                backend.quote_name(current_opts.pk.column),
+                                rel_table_alias,
+                                backend.quote_name(current_opts.object_name.lower() + '_id'))
+                        )
+
                         # Optimization: In the case of primary-key lookups, we
                         # don't have to do an extra join.
                         if lookup_list and lookup_list[0] == f.rel.to._meta.pk.name and lookup_type == 'exact':
@@ -251,14 +260,17 @@ def parse_lookup(kwarg_items, opts, table_count=0):
                             lookup_list.pop()
                             param_required = False
                         else:
-                            new_table_alias = 't%s' % table_count
-                            tables.append('%s %s' % (backend.quote_name(f.rel.to._meta.db_table),
-                                backend.quote_name(new_table_alias)))
-                            join_where.append('%s.%s = %s.%s' % \
-                                (backend.quote_name(rel_table_alias),
-                                backend.quote_name(f.rel.to._meta.object_name.lower() + '_id'),
-                                backend.quote_name(new_table_alias),
-                                backend.quote_name(f.rel.to._meta.pk.column)))
+                            new_table_alias = current_table_alias + LOOKUP_SEPARATOR + current
+
+                            joins[backend.quote_name(new_table_alias)] = (
+                                backend.quote_name(f.rel.to._meta.db_table),
+                                "INNER JOIN",
+                                '%s.%s = %s.%s' %
+                                    (rel_table_alias,
+                                    backend.quote_name(f.rel.to._meta.object_name.lower() + '_id'),
+                                    backend.quote_name(new_table_alias),
+                                    backend.quote_name(f.rel.to._meta.pk.column))
+                            )
                             current_table_alias = new_table_alias
                             param_required = True
                         current_opts = f.rel.to._meta
@@ -280,12 +292,17 @@ def parse_lookup(kwarg_items, opts, table_count=0):
                             where.append(get_where_clause(lookup_type, current_table_alias+'.', f.column, kwarg_value))
                             params.extend(f.get_db_prep_lookup(lookup_type, kwarg_value))
                         else:
-                            new_table_alias = 't%s' % table_count
-                            tables.append('%s %s' % \
-                                (backend.quote_name(f.rel.to._meta.db_table), backend.quote_name(new_table_alias)))
-                            join_where.append('%s.%s = %s.%s' % \
-                                (backend.quote_name(current_table_alias), backend.quote_name(f.column),
-                                backend.quote_name(new_table_alias), backend.quote_name(f.rel.to._meta.pk.column)))
+                            new_table_alias = current_table_alias + LOOKUP_SEPARATOR + current
+
+                            joins[backend.quote_name(new_table_alias)] = (
+                                backend.quote_name(f.rel.to._meta.db_table),
+                                "INNER JOIN",
+                                '%s.%s = %s.%s' %
+                                    (backend.quote_name(current_table_alias),
+                                    backend.quote_name(f.column),
+                                    backend.quote_name(new_table_alias),
+                                    backend.quote_name(f.rel.to._meta.pk.column))
+                            )
                             current_table_alias = new_table_alias
                             param_required = True
                         current_opts = f.rel.to._meta
@@ -301,4 +318,4 @@ def parse_lookup(kwarg_items, opts, table_count=0):
                 throw_bad_kwarg_error(kwarg)
             except StopIteration:
                 continue
-    return tables, join_where, where, params, table_count
+    return tables, joins, where, params

tests/modeltests/many_to_one/models.py

@@ -67,6 +67,19 @@ def __repr__(self):
 >>> Article.objects.get_list(reporter__first_name__exact='John', order_by=['pub_date'])
 [This is a test, John's second story]
 
+# Query twice over the related field.
+>>> Article.objects.get_list(reporter__first_name__exact='John', reporter__last_name__exact='Smith')
+[This is a test, John's second story]
+
+# The underlying query only makes one join when a related table is referenced twice.
+>>> null, sql, null = Article.objects._get_sql_clause(reporter__first_name__exact='John', reporter__last_name__exact='Smith')
+>>> sql.count('INNER JOIN')
+1
+
+# The automatically joined table has a predictable name.
+>>> Article.objects.get_list(reporter__first_name__exact='John', where=["many_to_one_articles__reporter.last_name='Smith'"])
+[This is a test, John's second story]
+
 # Find all Articles for the Reporter whose ID is 1.
 >>> Article.objects.get_list(reporter__id__exact=1, order_by=['pub_date'])
 [This is a test, John's second story]
@@ -95,4 +108,5 @@ def __repr__(self):
 >>> a4.save()
 >>> a4.get_reporter()
 John Smith
+
 """