add TruncDate support

Author: timgraham

README.md

@@ -203,7 +203,6 @@ Congratulations, your project is ready to go!
     - `Right`
     - `SHA1`, `SHA224`, `SHA256`, `SHA384`, `SHA512`
     - `Sign`
-    - `TruncDate`
     - `TruncTime`
 
 - The `tzinfo` parameter of the `Trunc` database functions doesn't work

django_mongodb/features.py

@@ -498,14 +498,14 @@ 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 database function not supported.": {
-            "aggregation.tests.AggregateTestCase.test_aggregation_default_using_date_from_database",
-            "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_trunc_date_func",
-            "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_trunc_date_none",
-            "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_trunc_lookup_name_sql_injection",
-            "expressions.tests.FieldTransformTests.test_multiple_transforms_in_values",
-            "model_fields.test_datetimefield.DateTimeFieldTests.test_lookup_date_with_use_tz",
+        "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",
         },
         "TruncTime database function not supported.": {

django_mongodb/functions.py

@@ -15,6 +15,7 @@
     ExtractYear,
     Now,
     TruncBase,
+    TruncDate,
 )
 from django.db.models.functions.math import Ceil, Cot, Degrees, Log, Power, Radians, Random, Round
 from django.db.models.functions.text import (
@@ -191,6 +192,15 @@ def trunc(self, compiler, connection):
     return {"$dateTrunc": lhs_mql}
 
 
+def trunc_date(self, compiler, connection):
+    # Cast to date rather than truncate to date.
+    lhs_mql = process_lhs(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}
+
+
 def register_functions():
     Cast.as_mql = cast
     Concat.as_mql = concat
@@ -212,4 +222,5 @@ def register_functions():
     Substr.as_mql = substr
     Trim.as_mql = trim("trim")
     TruncBase.as_mql = trunc
+    TruncDate.as_mql = trunc_date
     Upper.as_mql = preserve_null("toUpper")