Fix random order by issue (#142)

* Fix random order by issue

https://code.djangoproject.com/ticket/33531

* Fix `expr`== None issue

Author: absci

mssql/compiler.py

@@ -8,7 +8,7 @@
 from django.db.models.aggregates import Avg, Count, StdDev, Variance
 from django.db.models.expressions import Ref, Subquery, Value
 from django.db.models.functions import (
-    Chr, ConcatPair, Greatest, Least, Length, LPad, Repeat, RPad, StrIndex, Substr, Trim
+    Chr, ConcatPair, Greatest, Least, Length, LPad, Random, Repeat, RPad, StrIndex, Substr, Trim
 )
 from django.db.models.sql import compiler
 from django.db.transaction import TransactionManagementError
@@ -311,7 +311,13 @@ def as_sql(self, with_limits=True, with_col_aliases=False):
 
             if order_by:
                 ordering = []
-                for _, (o_sql, o_params, _) in order_by:
+                for expr, (o_sql, o_params, _) in order_by:
+                    if expr:
+                        src = next(iter(expr.get_source_expressions()))
+                        if isinstance(src, Random):
+                            # ORDER BY RAND() doesn't return rows in random order
+                            # replace it with NEWID()
+                            o_sql = o_sql.replace('RAND()', 'NEWID()')
                     ordering.append(o_sql)
                     params.extend(o_params)
                 result.append('ORDER BY %s' % ', '.join(ordering))

testapp/tests/test_fields.py

@@ -20,3 +20,17 @@ def test_order_by(self):
         names = Customer_name.objects.select_for_update().all()
         addresses = Customer_address.objects.filter(Customer_address='123 Main St', Customer_name__in=names)
         self.assertEqual(len(addresses), 1)
+
+    def test_random_order_by(self):
+        # https://code.djangoproject.com/ticket/33531
+        Customer_name.objects.bulk_create([
+            Customer_name(Customer_name='Jack'),
+            Customer_name(Customer_name='Jane'),
+            Customer_name(Customer_name='John'),
+        ])
+        names = []
+        # iterate 20 times to make sure we don't get the same result
+        for _ in range(20):
+            names.append(list(Customer_name.objects.order_by('?')))
+
+        self.assertNotEqual(names.count(names[0]), 20)