add support for comparison database functions

Author: timgraham

.github/workflows/test-python.yml

@@ -74,6 +74,7 @@ jobs:
           bulk_create
           dates
           datetimes
+          db_functions.comparison
           db_functions.datetime
           db_functions.math
           empty

django_mongodb/base.py

@@ -44,11 +44,12 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         "IntegerField": "int",
         "BigIntegerField": "long",
         "GenericIPAddressField": "string",
-        "NullBooleanField": "bool",
         "OneToOneField": "int",
+        "PositiveBigIntegerField": "int",
         "PositiveIntegerField": "long",
         "PositiveSmallIntegerField": "int",
         "SlugField": "string",
+        "SmallAutoField": "int",
         "SmallIntegerField": "int",
         "TextField": "string",
         "TimeField": "date",

django_mongodb/features.py

@@ -2,6 +2,8 @@
 
 
 class DatabaseFeatures(BaseDatabaseFeatures):
+    greatest_least_ignores_nulls = True
+    has_json_object_function = False
     supports_date_lookup_using_string = False
     supports_foreign_keys = False
     supports_ignore_conflicts = False
@@ -29,6 +31,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "lookup.tests.LookupTests.test_count",
         # Lookup in order_by() not supported:
         # unsupported operand type(s) for %: 'function' and 'str'
+        "db_functions.comparison.test_coalesce.CoalesceTests.test_ordering",
         "lookup.tests.LookupQueryingTests.test_lookup_in_order_by",
         # annotate() after values() doesn't raise NotSupportedError.
         "lookup.tests.LookupTests.test_exact_query_rhs_with_selected_columns",
@@ -50,6 +53,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         # the result back to UTC.
         "db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_trunc_func_with_timezone",
         "db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_trunc_timezone_applied_before_truncation",
+        # Coalesce() with expressions doesn't generate correct query.
+        "db_functions.comparison.test_coalesce.CoalesceTests.test_mixed_values",
     }
 
     django_test_skips = {
@@ -73,6 +78,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "QuerySet.update() with expression not supported.": {
             "annotations.tests.AliasTests.test_update_with_alias",
             "annotations.tests.NonAggregateAnnotationTestCase.test_update_with_annotation",
+            "db_functions.comparison.test_least.LeastTests.test_update",
+            "db_functions.comparison.test_greatest.GreatestTests.test_update",
             "model_fields.test_integerfield.PositiveIntegerFieldTests.test_negative_values",
             "timezones.tests.NewDatabaseTests.test_update_with_timedelta",
             "update.tests.AdvancedTests.test_update_annotated_queryset",
@@ -123,6 +130,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "queries.test_bulk_update.BulkUpdateTests.test_database_routing_batch_atomicity",
         },
         "Test assumes integer primary key.": {
+            "db_functions.comparison.test_cast.CastTests.test_cast_to_integer_foreign_key",
             "model_fields.test_foreignkey.ForeignKeyTests.test_to_python",
         },
         # https://github.com/mongodb-labs/django-mongodb/issues/12
@@ -160,6 +168,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "lookup.tests.LookupQueryingTests.test_filter_lookup_lhs",
             # Subquery not supported.
             "annotations.tests.NonAggregateAnnotationTestCase.test_empty_queryset_annotation",
+            "db_functions.comparison.test_coalesce.CoalesceTests.test_empty_queryset",
             "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_outerref",
             "db_functions.datetime.test_extract_trunc.DateFunctionTests.test_trunc_subquery_with_parameters",
             "lookup.tests.LookupQueryingTests.test_filter_subquery_lhs",
@@ -186,8 +195,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "annotations.tests.NonAggregateAnnotationTestCase.test_custom_functions_can_ref_other_functions",
             # Floor not implemented.
             "annotations.tests.NonAggregateAnnotationTestCase.test_custom_transform_annotation",
-            # Coalesce not implemented.
-            "annotations.tests.AliasTests.test_alias_annotation_expression",
+            # annotate() with expression that raises FullResultSet crashes.
             "annotations.tests.NonAggregateAnnotationTestCase.test_full_expression_wrapped_annotation",
             # BaseDatabaseOperations may require a format_for_duration_arithmetic().
             "annotations.tests.NonAggregateAnnotationTestCase.test_mixed_type_annotation_date_interval",
@@ -206,6 +214,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "annotations.tests.AliasTests.test_order_by_alias_aggregate",
             "annotations.tests.NonAggregateAnnotationTestCase.test_annotate_exists",
             "annotations.tests.NonAggregateAnnotationTestCase.test_annotate_with_aggregation",
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_db_datetime_to_date_group_by",
         },
         "QuerySet.dates() is not supported on MongoDB.": {
             "annotations.tests.AliasTests.test_dates_alias",
@@ -246,6 +255,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "annotations.tests.NonAggregateAnnotationTestCase.test_annotation_subquery_outerref_transform",
             "annotations.tests.NonAggregateAnnotationTestCase.test_annotation_with_m2m",
             "annotations.tests.NonAggregateAnnotationTestCase.test_chaining_annotation_filter_with_m2m",
+            "db_functions.comparison.test_least.LeastTests.test_related_field",
+            "db_functions.comparison.test_greatest.GreatestTests.test_related_field",
             "defer.tests.BigChildDeferTests.test_defer_baseclass_when_subclass_has_added_field",
             "defer.tests.BigChildDeferTests.test_defer_subclass",
             "defer.tests.BigChildDeferTests.test_defer_subclass_both",
@@ -331,4 +342,14 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "MongoDB can't annotate ($project) a function like PI().": {
             "db_functions.math.test_pi.PiTests.test",
         },
+        "Can't cast from date to datetime without MongoDB interpreting the new value in UTC.": {
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_db_date_to_datetime",
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_db_datetime_to_time",
+        },
+        "Casting Python literals doesn't work.": {
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_python",
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_python_to_date",
+            "db_functions.comparison.test_cast.CastTests.test_cast_from_python_to_datetime",
+            "db_functions.comparison.test_cast.CastTests.test_cast_to_duration",
+        },
     }

django_mongodb/functions.py

@@ -1,5 +1,6 @@
 from django.db import NotSupportedError
 from django.db.models.expressions import Func
+from django.db.models.functions.comparison import Cast, Coalesce, Greatest, Least, NullIf
 from django.db.models.functions.datetime import (
     Extract,
     ExtractDay,
@@ -21,7 +22,10 @@
 
 MONGO_OPERATORS = {
     Ceil: "ceil",
+    Coalesce: "ifNull",
     Degrees: "radiansToDegrees",
+    Greatest: "max",
+    Least: "min",
     Power: "pow",
     Radians: "degreesToRadians",
     Random: "rand",
@@ -41,6 +45,17 @@
 }
 
 
+def cast(self, compiler, connection):
+    output_type = connection.data_types[self.output_field.get_internal_type()]
+    lhs_mql = process_lhs(self, compiler, connection)[0]
+    if max_length := self.output_field.max_length:
+        lhs_mql = {"$substrCP": [lhs_mql, 0, max_length]}
+    lhs_mql = {"$convert": {"input": lhs_mql, "to": output_type}}
+    if decimal_places := getattr(self.output_field, "decimal_places", None):
+        lhs_mql = {"$trunc": [lhs_mql, decimal_places]}
+    return lhs_mql
+
+
 def cot(self, compiler, connection):
     lhs_mql = process_lhs(self, compiler, connection)
     return {"$divide": [1, {"$tan": lhs_mql}]}
@@ -69,6 +84,12 @@ def log(self, compiler, connection):
     return func(clone, compiler, connection)
 
 
+def null_if(self, compiler, connection):
+    """Return None if expr1==expr2 else expr1."""
+    expr1, expr2 = (expr.as_mql(compiler, connection) for expr in self.get_source_expressions())
+    return {"$cond": {"if": {"$eq": [expr1, expr2]}, "then": None, "else": expr1}}
+
+
 def round_(self, compiler, connection):
     # Round needs its own function because it's a special case that inherits
     # from Transform but has two arguments.
@@ -84,9 +105,11 @@ def trunc(self, compiler, connection):
 
 
 def register_functions():
+    Cast.as_mql = cast
     Cot.as_mql = cot
     Extract.as_mql = extract
     Func.as_mql = func
     Log.as_mql = log
+    NullIf.as_mql = null_if
     Round.as_mql = round_
     TruncBase.as_mql = trunc