Added some contorted post-processing to include null check in IS KNOW…

…N queries

optimade/filtertransformers/mongo.py

@@ -40,6 +40,7 @@ def postprocess(self, query):
 
         query = self._apply_relationship_filtering(query)
         query = self._apply_length_operators(query)
+        query = self._apply_unknown_or_null_filter(query)
 
         return query
 
@@ -134,7 +135,10 @@ def value_op_rhs(self, operator, value):
 
     def known_op_rhs(self, arg):
         # known_op_rhs: IS ( KNOWN | UNKNOWN )
-        return {"$exists": arg[1] == "KNOWN"}
+        # The OPTIMADE spec also required a type comparison with null, this must be post-processed
+        # so here we use a special key "#known" which will get replaced in post-processing with the
+        # expanded dict
+        return {"#known": arg[1] == "KNOWN"}
 
     def fuzzy_string_op_rhs(self, arg):
         # fuzzy_string_op_rhs: CONTAINS value | STARTS [ WITH ] value | ENDS [ WITH ] value
@@ -389,6 +393,45 @@ def replace_with_relationship(subdict, prop, expr):
             filter_, check_for_entry_type, replace_with_relationship
         )
 
+    def _apply_unknown_or_null_filter(self, filter_: dict) -> dict:
+        """ This method loops through the query and replaces the check for
+        KNOWN with a check for existence and a check for not null, and the
+        inverse for UNKNOWN.
+
+        """
+
+        def check_for_known_filter(prop, expr):
+            """ Find cases where the query dict looks like
+            `{"field": {"#known": T/F}}` or
+            `{"field": "$not": {"#known": T/F}}`, which is a magic word
+            for KNOWN/UNKNOWN filters in this transformer.
+
+            """
+            return isinstance(expr, dict) and (
+                "#known" in expr or "#known" in expr.get("$not", {})
+            )
+
+        def replace_known_filter_with_or(subdict, prop, expr):
+            nor = set(expr.keys()) == {"$not"}
+            if nor:
+                expr = expr["$not"]
+            if "$or" not in subdict:
+                subdict["$or"] = []
+
+            known = expr["#known"]
+            subdict["$or"].append({prop: {"$exists": known ^ nor}})
+            subdict["$or"].append(
+                {prop: {"$type": {"$ne" if known ^ nor else "$eq": "null"}}}
+            )
+
+            subdict.pop(prop)
+
+            return subdict
+
+        return recursive_postprocessing(
+            filter_, check_for_known_filter, replace_known_filter_with_or
+        )
+
 
 def recursive_postprocessing(filter_, condition, replacement):
     """ Recursively descend into the query, checking each dictionary

tests/filtertransformers/test_mongo.py

@@ -598,24 +598,85 @@ def test_list_properties(self):
             },
         )
 
-    def test_properties(self):
+    def test_known_properties(self):
         #  Filtering on Properties with unknown value
-        # TODO: {'$not': {'$exists': False}} can be simplified to {'$exists': True}
-        # The { $not: { $gt: 1.99 } } is different from the $lte operator. { $lte: 1.99 } returns only the documents
-        # where price field exists and its value is less than or equal to 1.99.
-        # Remember that the $not operator only affects other operators and cannot check fields and documents
-        # independently. So, use the $not operator for logical disjunctions and the $ne operator to test
-        # the contents of fields directly.
-        # source: https://docs.mongodb.com/manual/reference/operator/query/not/
+        self.assertEqual(
+            self.transform("chemical_formula_anonymous IS UNKNOWN"),
+            {
+                "$or": [
+                    {"chemical_formula_anonymous": {"$exists": False}},
+                    {"chemical_formula_anonymous": {"$type": {"$eq": "null"}}},
+                ]
+            },
+        )
+        self.assertEqual(
+            self.transform("chemical_formula_anonymous IS KNOWN"),
+            {
+                "$or": [
+                    {"chemical_formula_anonymous": {"$exists": True}},
+                    {"chemical_formula_anonymous": {"$type": {"$ne": "null"}}},
+                ]
+            },
+        )
+        self.assertEqual(
+            self.transform("NOT chemical_formula_anonymous IS UNKNOWN"),
+            {
+                "$or": [
+                    {"chemical_formula_anonymous": {"$exists": True}},
+                    {"chemical_formula_anonymous": {"$type": {"$ne": "null"}}},
+                ]
+            },
+        )
+        self.assertEqual(
+            self.transform("NOT chemical_formula_anonymous IS KNOWN"),
+            {
+                "$or": [
+                    {"chemical_formula_anonymous": {"$exists": False}},
+                    {"chemical_formula_anonymous": {"$type": {"$eq": "null"}}},
+                ]
+            },
+        )
 
         self.assertEqual(
             self.transform(
                 "chemical_formula_hill IS KNOWN AND NOT chemical_formula_anonymous IS UNKNOWN"
             ),
             {
                 "$and": [
-                    {"chemical_formula_hill": {"$exists": True}},
-                    {"chemical_formula_anonymous": {"$not": {"$exists": False}}},
+                    {
+                        "$or": [
+                            {"chemical_formula_hill": {"$exists": True}},
+                            {"chemical_formula_hill": {"$type": {"$ne": "null"}}},
+                        ]
+                    },
+                    {
+                        "$or": [
+                            {"chemical_formula_anonymous": {"$exists": True}},
+                            {"chemical_formula_anonymous": {"$type": {"$ne": "null"}}},
+                        ]
+                    },
+                ]
+            },
+        )
+
+        self.assertEqual(
+            self.transform(
+                "chemical_formula_hill IS KNOWN AND chemical_formula_anonymous IS UNKNOWN"
+            ),
+            {
+                "$and": [
+                    {
+                        "$or": [
+                            {"chemical_formula_hill": {"$exists": True}},
+                            {"chemical_formula_hill": {"$type": {"$ne": "null"}}},
+                        ]
+                    },
+                    {
+                        "$or": [
+                            {"chemical_formula_anonymous": {"$exists": False}},
+                            {"chemical_formula_anonymous": {"$type": {"$eq": "null"}}},
+                        ]
+                    },
                 ]
             },
         )