Fixed #20583 -- ORM always uses setup_joins() for join generation

There were a couple of places which used Query.join() directly. By
using setup_joins() in these places the code is more DRY, and in
addition there is no need to directly call field.get_joining_columns()
unless the field is the given join_field from get_path_info(). This
makes it easier to make sure a ForeignObject subclass generates joins
correctly in all cases.

django/db/models/sql/compiler.py

@@ -631,12 +631,10 @@ class SQLCompiler(object):
             if not select_related_descend(f, restricted, requested,
                                           only_load.get(field_model)):
                 continue
-            table = f.rel.to._meta.db_table
             promote = nullable or f.null
-            alias = self.query.join_parent_model(opts, model, root_alias, {})
-            join_cols = f.get_joining_columns()
-            alias = self.query.join((alias, table, join_cols),
-                    outer_if_first=promote, join_field=f)
+            _, _, _, joins, _ = self.query.setup_joins(
+                [f.name], opts, root_alias, outer_if_first=promote)
+            alias = joins[-1]
             columns, aliases = self.get_default_columns(start_alias=alias,
                     opts=f.rel.to._meta, as_pairs=True)
             self.query.related_select_cols.extend(
@@ -660,12 +658,9 @@ class SQLCompiler(object):
                                               only_load.get(model), reverse=True):
                     continue
 
-                alias = self.query.join_parent_model(opts, f.rel.to, root_alias, {})
-                table = model._meta.db_table
-                alias = self.query.join(
-                    (alias, table, f.get_joining_columns(reverse_join=True)),
-                    outer_if_first=True, join_field=f
-                )
+                _, _, _, joins, _ = self.query.setup_joins(
+                    [f.related_query_name()], opts, root_alias, outer_if_first=True)
+                alias = joins[-1]
                 from_parent = (opts.model if issubclass(model, opts.model)
                                else None)
                 columns, aliases = self.get_default_columns(start_alias=alias,
@@ -677,7 +672,7 @@ class SQLCompiler(object):
                 # Use True here because we are looking at the _reverse_ side of
                 # the relation, which is always nullable.
                 new_nullable = True
-
+                table = model._meta.db_table
                 self.fill_related_selections(model._meta, table, cur_depth+1,
                     next, restricted, new_nullable)
 

django/db/models/sql/query.py

@@ -926,10 +926,10 @@ class Query(object):
         """
         if model in seen:
             return seen[model]
-        int_opts = opts
         chain = opts.get_base_chain(model)
         if chain is None:
             return alias
+        curr_opts = opts
         for int_model in chain:
             if int_model in seen:
                 return seen[int_model]
@@ -937,14 +937,14 @@ class Query(object):
             # with no parents, assign the new options
             # object and skip to the next base in that
             # case
-            if not int_opts.parents[int_model]:
-                int_opts = int_model._meta
+            if not curr_opts.parents[int_model]:
+                curr_opts = int_model._meta
                 continue
-            link_field = int_opts.get_ancestor_link(int_model)
-            int_opts = int_model._meta
-            connection = (alias, int_opts.db_table, link_field.get_joining_columns())
-            alias = seen[int_model] = self.join(connection, nullable=False,
-                                                join_field=link_field)
+            link_field = curr_opts.get_ancestor_link(int_model)
+            _, _, _, joins, _ = self.setup_joins(
+                [link_field.name], curr_opts, alias)
+            curr_opts = int_model._meta
+            alias = seen[int_model] = joins[-1]
         return alias or seen[None]
 
     def remove_inherited_models(self):
@@ -1321,7 +1321,7 @@ class Query(object):
         return path, final_field, targets
 
     def setup_joins(self, names, opts, alias, can_reuse=None, allow_many=True,
-                    allow_explicit_fk=False):
+                    allow_explicit_fk=False, outer_if_first=False):
         """
         Compute the necessary table joins for the passage through the fields
         given in 'names'. 'opts' is the Options class for the current model
@@ -1364,8 +1364,9 @@ class Query(object):
                 nullable = True
             connection = alias, opts.db_table, join.join_field.get_joining_columns()
             reuse = can_reuse if join.m2m else None
-            alias = self.join(connection, reuse=reuse,
-                              nullable=nullable, join_field=join.join_field)
+            alias = self.join(
+                connection, reuse=reuse, nullable=nullable, join_field=join.join_field,
+                outer_if_first=outer_if_first)
             joins.append(alias)
         if hasattr(final_field, 'field'):
             final_field = final_field.field