Added support for SortBy operator to simplify the creation of sort in…

…structions.

mongoframes/queries.py

@@ -4,6 +4,7 @@
 
 import re
 
+from pymongo import (ASCENDING, DESCENDING)
 
 __all__ = [
     # Queries
@@ -24,6 +25,9 @@
     'Or',
     'Nor',
 
+    # Sorting
+    'SortBy',
+
     # Utils
     'to_refs'
     ]
@@ -240,6 +244,20 @@ class Nor(Group):
     operator = '$nor'
 
 
+# Sorting
+
+def SortBy(*qs):
+    """Convert a list of Q objects into list of sort instructions"""
+
+    sort = []
+    for q in qs:
+        if q._path.endswith('.desc'):
+            sort.append((q._path[:-5], DESCENDING))
+        else:
+            sort.append((q._path, ASCENDING))
+    return sort
+
+
 # Utils
 
 def deep_merge(source, dest):

setup.py

@@ -83,7 +83,7 @@
     # https://packaging.python.org/en/latest/requirements.html
     install_requires=[
         'blinker>=1.4',
-        'Faker>=0.7.7',
+        'Faker>=0.7.18',
         'pymongo>=3'
         ],
 

tests/test_queries.py

@@ -97,6 +97,12 @@ def test_nor():
     assert Nor(Q.foo == 123, Q.bar != 456).to_dict() == \
         {'$nor': [{'foo': 123}, {'bar': {'$ne': 456}}]}
 
+# Sorting
+
+def test_sort_by():
+    """Should return sort instructions for a list of `Q` instances"""
+    assert SortBy(Q.dob.desc, Q.name) == [('dob', -1), ('name', 1)]
+
 
 # Utils