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

@@ -469,14 +469,8 @@ 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",
+        "TruncDate database function's tzinfo not supported.": {
             "model_fields.test_datetimefield.DateTimeFieldTests.test_lookup_date_with_use_tz",
-            "model_fields.test_datetimefield.DateTimeFieldTests.test_lookup_date_without_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 +192,27 @@ 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 tzinfo ({tzname}) isn't supported on MongoDB.")
+    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 register_functions():
     Cast.as_mql = cast
     Concat.as_mql = concat
@@ -212,4 +234,5 @@ 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")