Update compare_values to support null values (#26)

CHANGELOG.md

@@ -9,7 +9,7 @@ Documentation of release versions of `nacc-form-validator`
 * Updates `compare_with` to support the `abs` operator
 * Updates `compatibility` error message to be more verbose
 * Refactors the tests to be more modularized so that they're more manageable
-* Refactors logic for `compare_values` by moving it to its own utility method
+* Refactors logic for `compare_values` by moving it to its own utility method and allows comparing to null values
 * Adds `get_previous_record` method to grab previous record from Datastore, which can grab the previous record or the previous record where a specific field is non-empty
 	* Updates `_validate_temporalrules` to also support the `ignore_empty` parameter
 * Adds support for comparing against the previous record in `compare_with`

nacc_form_validator/utils.py

@@ -68,6 +68,23 @@ def compare_values(comparator: str, value: object, base_value: object) -> bool:
     Returns:
         bool: True if the formula is satisfied, else False
     """
+    # test these first as they don't care about null values
+    if comparator == "==":
+        return value == base_value
+
+    if comparator == "!=":
+        return value != base_value
+
+    # for < and >, follow same convention as jsonlogic for null values
+    # for >= and <=, allow equality case (both None)
+    if value is None and base_value is None:
+        return True if comparator in ["<=", ">="] else False
+    if value is None:
+        return True if comparator in ["<", "<="] else False
+    if base_value is None:
+        return False if comparator in ["<", "<="] else True
+
+    # now try as normal
     if comparator == ">=":
         return value >= base_value
 
@@ -80,10 +97,4 @@ def compare_values(comparator: str, value: object, base_value: object) -> bool:
     if comparator == "<":
         return value < base_value
 
-    if comparator == "==":
-        return value == base_value
-
-    if comparator == "!=":
-        return value != base_value
-
-    return False
+    raise TypeError(f"Unrecognized comparator: {comparator}")

tests/test_utils.py

@@ -110,10 +110,10 @@ def test_compare_values_date_invalid():
     assert not compare_values("!=", parser.parse("01/01/2000"), parser.parse("01/01/2000"))
 
 def test_compare_values_type_error():
-    """ Test comparing two values of incompatible types """
+    """ Test comparing two values of incompatible types or unrecognized comparator """
     with pytest.raises(TypeError) as e:
-        compare_values("<", None, "hello")
-    assert str(e.value) == "'<' not supported between instances of 'NoneType' and 'str'"
+        compare_values("*", 5, 10)
+    assert str(e.value) == "Unrecognized comparator: *"
 
     with pytest.raises(TypeError) as e:
         compare_values("<", 5, parser.parse("01/01/2000"))
@@ -122,3 +122,25 @@ def test_compare_values_type_error():
     with pytest.raises(TypeError) as e:
         compare_values("<", "01/01/2000", parser.parse("01/01/2000"))
     assert str(e.value) == "'<' not supported between instances of 'str' and 'datetime.datetime'"
+
+def test_compare_values_null_values_valid():
+    """ Test comparing when at least one of the values is null """
+    assert compare_values("==", None, None)
+    assert not compare_values("==", None, 5)
+    assert not compare_values("!=", None, None)
+    assert compare_values("!=", 5, None)
+
+    assert compare_values("<", None, 5)
+    assert not compare_values("<", 5, None)
+    assert not compare_values(">", None, 5)
+    assert compare_values(">", 5, None)
+
+    assert compare_values("<=", None, 5)
+    assert not compare_values("<=", 5, None)
+    assert not compare_values(">=", None, 5)
+    assert compare_values(">=", 5, None)
+
+    assert not compare_values("<", None, None)
+    assert not compare_values(">", None, None)
+    assert compare_values("<=", None, None)
+    assert compare_values(">=", None, None)