Added Query.join_parent_model()

This simplifies especially compiler.py a lot, where almost the same
code was repeated multiple times.

Refs #19385

2 files changed, 37 insertions, 61 deletions

diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py
index b0fb933705..16aa031e59 100644
--- a/django/db/models/sql/compiler.py
+++ b/django/db/models/sql/compiler.py
@@ -261,27 +261,14 @@ class SQLCompiler(object):
         qn2 = self.connection.ops.quote_name
         aliases = set()
         only_load = self.deferred_to_columns()
-
+        seen = self.query.included_inherited_models.copy()
         if start_alias:
-            seen = {None: start_alias}
+            seen[None] = start_alias
         for field, model in opts.get_fields_with_model():
             if from_parent and model is not None and issubclass(from_parent, model):
                 # Avoid loading data for already loaded parents.
                 continue
-            if start_alias:
-                try:
-                    alias = seen[model]
-                except KeyError:
-                    link_field = opts.get_ancestor_link(model)
-                    alias = self.query.join((start_alias, model._meta.db_table,
-                            link_field.column, model._meta.pk.column),
-                            join_field=link_field)
-                    seen[model] = alias
-            else:
-                # If we're starting from the base model of the queryset, the
-                # aliases will have already been set up in pre_sql_setup(), so
-                # we can save time here.
-                alias = self.query.included_inherited_models[model]
+            alias = self.query.join_parent_model(opts, model, start_alias, seen)
             table = self.query.alias_map[alias].table_name
             if table in only_load and field.column not in only_load[table]:
                 continue
@@ -623,26 +610,7 @@ class SQLCompiler(object):
                 continue
             table = f.rel.to._meta.db_table
             promote = nullable or f.null
-            if model:
-                int_opts = opts
-                alias = root_alias
-                alias_chain = []
-                for int_model in opts.get_base_chain(model):
-                    # Proxy model have elements in base chain
-                    # 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
-                        continue
-                    lhs_col = int_opts.parents[int_model].column
-                    link_field = int_opts.get_ancestor_link(int_model)
-                    int_opts = int_model._meta
-                    alias = self.query.join((alias, int_opts.db_table, lhs_col,
-                            int_opts.pk.column), promote=promote, join_field=link_field)
-                    alias_chain.append(alias)
-            else:
-                alias = root_alias
+            alias = self.query.join_parent_model(opts, model, root_alias, {})
 
             alias = self.query.join((alias, table, f.column,
                     f.rel.get_related_field().column),
@@ -670,28 +638,8 @@ 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
-                int_opts = opts
-                alias = root_alias
-                alias_chain = []
-                chain = opts.get_base_chain(f.rel.to)
-                if chain is not None:
-                    for int_model in chain:
-                        # Proxy model have elements in base chain
-                        # 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
-                            continue
-                        lhs_col = int_opts.parents[int_model].column
-                        link_field = int_opts.get_ancestor_link(int_model)
-                        int_opts = int_model._meta
-                        alias = self.query.join(
-                            (alias, int_opts.db_table, lhs_col, int_opts.pk.column),
-                            promote=True, join_field=link_field
-                        )
-                        alias_chain.append(alias)
                 alias = self.query.join(
                     (alias, table, f.rel.get_related_field().column, f.column),
                     promote=True, join_field=f
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index e5833b2b51..2546d6c889 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1004,12 +1004,40 @@ class Query(object):
 
         for field, model in opts.get_fields_with_model():
             if model not in seen:
-                link_field = opts.get_ancestor_link(model)
-                seen[model] = self.join(
-                    (root_alias, model._meta.db_table, link_field.column,
-                     model._meta.pk.column), join_field=link_field)
+                self.join_parent_model(opts, model, root_alias, seen)
         self.included_inherited_models = seen
 
+    def join_parent_model(self, opts, model, alias, seen):
+        """
+        Makes sure the given 'model' is joined in the query. If 'model' isn't
+        a parent of 'opts' or if it is None this method is a no-op.
+
+        The 'alias' is the root alias for starting the join, 'seen' is a dict
+        of model -> alias of existing joins.
+        """
+        if model in seen:
+            return seen[model]
+        int_opts = opts
+        chain = opts.get_base_chain(model)
+        if chain is None:
+            return alias
+        for int_model in chain:
+            if int_model in seen:
+                return seen[int_model]
+            # Proxy model have elements in base chain
+            # 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
+                continue
+            link_field = int_opts.get_ancestor_link(int_model)
+            int_opts = int_model._meta
+            connection = (alias, int_opts.db_table, link_field.column, int_opts.pk.column)
+            alias = seen[int_model] = self.join(connection, nullable=False,
+                                                join_field=link_field)
+        return alias
+
     def remove_inherited_models(self):
         """
         Undoes the effects of setup_inherited_models(). Should be called