diff --git a/sqlalchemy_utils/batch.py b/sqlalchemy_utils/batch.py
index 620fa95..bbbca33 100644
--- a/sqlalchemy_utils/batch.py
+++ b/sqlalchemy_utils/batch.py
@@ -37,31 +37,33 @@ class with_backrefs(object):
         self.path = path
 
 
+
+
+
 class Path(object):
     """
     A class that represents an attribute path.
     """
     def __init__(self, entities, prop, populate_backrefs=False):
+        self.validate_property(prop)
         self.property = prop
         self.entities = entities
         self.populate_backrefs = populate_backrefs
+        self.fetcher = self.fetcher_class(self)
+
+    def validate_property(self, prop):
         if (
-            not isinstance(self.property, RelationshipProperty) and
-            not isinstance(self.property, GenericRelationshipProperty)
+            not isinstance(prop, RelationshipProperty) and
+            not isinstance(prop, GenericRelationshipProperty)
         ):
             raise PathException(
                 'Given attribute is not a relationship property.'
             )
-        self.fetcher = self.fetcher_class(self)
 
     @property
     def session(self):
         return object_session(self.entities[0])
 
-    @property
-    def parent_model(self):
-        return self.entities[0].__class__
-
     @property
     def model(self):
         return self.property.mapper.class_
@@ -267,7 +269,7 @@ class Fetcher(object):
         )
         for value in related_entities:
             backref_dict[local_values(self.prop, value[0])].append(
-                self.path.session.query(self.path.parent_model).get(
+                self.path.session.query(self.path.entities[0].__class__).get(
                     tuple(value[1:])
                 )
             )
diff --git a/sqlalchemy_utils/functions/orm.py b/sqlalchemy_utils/functions/orm.py
index 14f4e09..609eeab 100644
--- a/sqlalchemy_utils/functions/orm.py
+++ b/sqlalchemy_utils/functions/orm.py
@@ -2,6 +2,10 @@ from functools import partial
 from funcy import first
 from toolz import curry
 import sqlalchemy as sa
+from sqlalchemy import inspect
+from sqlalchemy.orm.query import _ColumnEntity
+from sqlalchemy.orm.mapper import Mapper
+from sqlalchemy.orm.util import AliasedInsp
 
 
 def remove_property(class_, name):
@@ -123,6 +127,83 @@ def remote_column_names(prop):
                     yield remote.name
 
 
+
+def query_labels(query):
+    """
+    Return all labels for given SQLAlchemy query object.
+
+    Example::
+
+
+        query = session.query(
+            Category,
+            db.func.count(Article.id).label('articles')
+        )
+
+        query_labels(query)  # ('articles', )
+
+    :param query: SQLAlchemy Query object
+    """
+    for entity in query._entities:
+        if isinstance(entity, _ColumnEntity) and entity._label_name:
+            yield entity._label_name
+
+
+def query_entities(query):
+    """
+    Return all entities for given SQLAlchemy query object.
+
+    Example::
+
+
+        query = session.query(
+            Category
+        )
+
+        query_entities(query)  # ('Category', )
+
+    :param query: SQLAlchemy Query object
+    """
+    for entity in query._entities:
+        yield entity.entity_zero.class_
+
+    for entity in query._join_entities:
+        if isinstance(entity, Mapper):
+            yield entity.class_
+        else:
+            yield entity
+
+
+def get_query_entity_by_alias(query, alias):
+    entities = query_entities(query)
+    if not alias:
+        return first(entities)
+
+    for entity in entities:
+        if isinstance(entity, AliasedInsp):
+            name = entity.name
+        else:
+            name = entity.__table__.name
+
+        if name == alias:
+            return entity
+
+
+def attrs(expr):
+    if isinstance(expr, AliasedInsp):
+        return expr.mapper.attrs
+    else:
+        return inspect(expr).attrs
+
+
+def get_expr_attr(expr, attr_name):
+    if isinstance(expr, AliasedInsp):
+        return getattr(expr.selectable.c, attr_name)
+    else:
+        return getattr(expr, attr_name)
+
+
+
 def declarative_base(model):
     """
     Returns the declarative base for given model class.
diff --git a/sqlalchemy_utils/functions/sort_query.py b/sqlalchemy_utils/functions/sort_query.py
index 468b774..281153f 100644
--- a/sqlalchemy_utils/functions/sort_query.py
+++ b/sqlalchemy_utils/functions/sort_query.py
@@ -1,23 +1,13 @@
-from sqlalchemy import inspect
-from sqlalchemy.orm.mapper import Mapper
 from sqlalchemy.orm.properties import ColumnProperty
-from sqlalchemy.orm.query import _ColumnEntity
-from sqlalchemy.orm.util import AliasedInsp
 from sqlalchemy.sql.expression import desc, asc, Label
-
-
-def attrs(expr):
-    if isinstance(expr, AliasedInsp):
-        return expr.mapper.attrs
-    else:
-        return inspect(expr).attrs
-
-
-def sort_expression(expr, attr_name):
-    if isinstance(expr, AliasedInsp):
-        return getattr(expr.selectable.c, attr_name)
-    else:
-        return getattr(expr, attr_name)
+from sqlalchemy.orm.util import AliasedInsp
+from .orm import (
+    attrs,
+    query_labels,
+    query_entities,
+    get_query_entity_by_alias,
+    get_expr_attr
+)
 
 
 class QuerySorterException(Exception):
@@ -31,57 +21,20 @@ class QuerySorter(object):
         self.separator = separator
         self.silent = silent
 
-    def inspect_labels_and_entities(self):
-        for entity in self.query._entities:
-            # get all label names for queries such as:
-            # db.session.query(
-            #       Category,
-            #       db.func.count(Article.id).label('articles')
-            # )
-            if isinstance(entity, _ColumnEntity) and entity._label_name:
-                self.labels.append(entity._label_name)
-            else:
-                self.entities.append(entity.entity_zero.class_)
-
-        for mapper in self.query._join_entities:
-            if isinstance(mapper, Mapper):
-                self.entities.append(mapper.class_)
-            else:
-                self.entities.append(mapper)
-
-    def get_entity_by_alias(self, alias):
-        if not alias:
-            return self.entities[0]
-
-        for entity in self.entities:
-            if isinstance(entity, AliasedInsp):
-                name = entity.name
-            else:
-                name = entity.__table__.name
-
-            if name == alias:
-                return entity
-
-    def assign_order_by(self, sort):
-        if not sort:
-            return self.query
-
-        sort = self.parse_sort_arg(sort)
+    def assign_order_by(self, entity, attr, func):
         expr = None
-        if sort['attr'] in self.labels:
-            expr = sort['attr']
+        if attr in self.labels:
+            expr = attr
         else:
-            entity = self.get_entity_by_alias(sort['entity'])
+            entity = get_query_entity_by_alias(self.query, entity)
             if entity:
-                expr = self.order_by_attr(entity, sort['attr'])
+                expr = self.order_by_attr(entity, attr)
 
         if expr is not None:
-            return self.query.order_by(
-                sort['func'](expr)
-            )
+            return self.query.order_by(func(expr))
         if not self.silent:
             raise QuerySorterException(
-                "Could not sort query with expression '%s'" % sort['attr']
+                "Could not sort query with expression '%s'" % attr
             )
         return self.query
 
@@ -93,7 +46,7 @@ class QuerySorter(object):
                 if isinstance(property_.columns[0], Label):
                     expr = property_.columns[0].name
                 else:
-                    expr = sort_expression(entity, property_.key)
+                    expr = get_expr_attr(entity, property_.key)
                 return expr
             else:
                 return
@@ -119,9 +72,14 @@ class QuerySorter(object):
 
     def __call__(self, query, *args):
         self.query = query
-        self.inspect_labels_and_entities()
+        self.labels = query_labels(query)
+        self.entities = query_entities(query)
         for sort in args:
-            self.query = self.assign_order_by(sort)
+            if not sort:
+                continue
+            self.query = self.assign_order_by(
+                **self.parse_sort_arg(sort)
+            )
         return self.query