Fix issue 81

reladiff/hashdiff_tables.py

@@ -1,7 +1,8 @@
 import os
+from functools import cmp_to_key
 from numbers import Number
 import logging
-from typing import Iterator
+from typing import Iterator, Sequence, Tuple
 from operator import attrgetter
 from collections import Counter
 from itertools import chain
@@ -27,6 +28,33 @@
 logger = logging.getLogger("hashdiff_tables")
 
 
+def compare_element(a, b):
+    """Compare a and b, treat None as the smallest value.
+
+    Return -1 if a < b, 0 if a == b and 1 if a > b.
+    """
+    if a == b:
+        return 0
+    if b is not None and ((a is None) or (a < b)):
+        return -1
+    return 1
+
+
+def compare(a: Tuple[str, Sequence], b: Tuple[str, Sequence]) -> int:
+    """Compare two sequences of the same length.
+
+    Compare a and b until the first element a[1][i] differs from b[1][i].
+    See compare_element() for detailed comparison rules.
+
+    Return -1 if a < b, 0 if a == b and 1 if a > b.
+    """
+    for i in range(len(a[1])):
+        res = compare_element(a[1][i], b[1][i])
+        if res != 0:
+            return res
+    return 0
+
+
 def diff_sets(a: list, b: list, skip_sort_results: bool, duplicate_rows_support: bool) -> Iterator:
     if duplicate_rows_support:
         c = Counter(b)
@@ -36,8 +64,7 @@ def diff_sets(a: list, b: list, skip_sort_results: bool, duplicate_rows_support:
         sa = set(a)
         sb = set(b)
         diff = chain((("-", x) for x in sa - sb), (("+", x) for x in sb - sa))
-
-    return diff if skip_sort_results else sorted(diff, key=lambda i: i[1])   # sort by key
+    return diff if skip_sort_results else sorted(diff, key=cmp_to_key(compare))  # sort by key
 
 
 @dataclass(frozen=True)

tests/test_diff_tables.py

@@ -6,7 +6,7 @@
 from sqeleton.queries import table, this, commit
 from sqeleton.utils import ArithAlphanumeric, numberToAlphanum
 
-from reladiff.hashdiff_tables import HashDiffer
+from reladiff.hashdiff_tables import HashDiffer, compare_element, diff_sets
 from reladiff.joindiff_tables import JoinDiffer
 from reladiff.table_segment import TableSegment, split_space, Vector
 from reladiff import databases as db
@@ -1071,3 +1071,29 @@ def test_compound_key(self):
         self.assertEqual(diff, [("-", (uuid, "9", "9")), ("+", (uuid, "9000", "9"))])
 
         self.assertRaises(ValueError, list, differ.diff_tables(aa, a))
+
+
+class TestDiffSets(unittest.TestCase):
+    def test_compare_element(self):
+        self.assertEqual(compare_element(None, 1), -1)
+        self.assertEqual(compare_element(1, 2), -1)
+        self.assertEqual(compare_element(None, 2), -1)
+        self.assertEqual(compare_element(None, None), 0)
+        self.assertEqual(compare_element(1, 1), 0)
+        self.assertEqual(compare_element(2, 2), 0)
+        self.assertEqual(compare_element(1, None), 1)
+        self.assertEqual(compare_element(2, 1), 1)
+        self.assertEqual(compare_element(2, None), 1)
+        self.assertEqual(compare_element(None, ''), -1)
+        self.assertEqual(compare_element('', ''), 0)
+        self.assertEqual(compare_element('', None), 1)
+
+    def test_diff_sets(self):
+        res = diff_sets([(1, None)], [(1, '')], skip_sort_results=False, duplicate_rows_support=True)
+        self.assertSequenceEqual(res, [('-', (1, None)), ('+', (1, ''))])
+
+        res = diff_sets([(1, '')], [(1, None)], skip_sort_results=False, duplicate_rows_support=True)
+        self.assertSequenceEqual(res, [('+', (1, None)), ('-', (1, ''))])
+
+        res = diff_sets([(1, None), (1, None)], [(1, None)], skip_sort_results=False, duplicate_rows_support=True)
+        self.assertSequenceEqual(res, [('-', (1, None))])