better approach for TruncDate

Author: timgraham

django_mongodb/features.py

@@ -502,12 +502,6 @@ def django_test_expected_failures(self):
             "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_quarter_func",
             "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_quarter_func_boundaries",
         },
-        "TruncDate comparison against datetime.date() doesn't work": {
-            # field__date=date() generates a type mismatch:
-            # {'$eq': [{'$toDate': '$dt'}, datetime.datetime(2014, 3, 12, 0, 0)]}
-            # since DatabaseOperations.adapt_datefield_value() converts the date.
-            "model_fields.test_datetimefield.DateTimeFieldTests.test_lookup_date_without_use_tz",
-        },
         "TruncDate database function with timezone not supported.": {
             "model_fields.test_datetimefield.DateTimeFieldTests.test_lookup_date_with_use_tz",
             "timezones.tests.NewDatabaseTests.test_query_convert_timezones",

django_mongodb/functions.py

@@ -199,7 +199,19 @@ def trunc_date(self, compiler, connection):
     tzname = self.get_tzname()
     if tzname and tzname != "UTC":
         raise NotSupportedError(f"TruncDate with timezone ({tzname}) isn't supported on MongoDB.")
-    return {"$toDate": lhs_mql}
+    return {
+        "$dateFromString": {
+            "dateString": {
+                "$concat": [
+                    {"$dateToString": {"format": "%Y-%m-%d", "date": lhs_mql}},
+                    # Dates are stored with time(0, 0), so by replacing any
+                    # existing time component with that, the result of
+                    # TruncDate can be compared to DateField.
+                    "T00:00:00.000",
+                ]
+            },
+        }
+    }
 
 
 def trunc_time(self, compiler, connection):
@@ -208,7 +220,7 @@ def trunc_time(self, compiler, connection):
         "$dateFromString": {
             "dateString": {
                 "$concat": [
-                    # Times are stored with datetime.min.date(), so by
+                    # Times are stored with date(1, 1, 1)), so by
                     # replacing any existing date component with that, the
                     # result of TruncTime can be compared to TimeField.
                     "0001-01-01T",