Translations around DateOnly.DayNumber

src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlDateTimeMemberTranslator.cs

@@ -56,6 +56,11 @@ public NpgsqlDateTimeMemberTranslator(IRelationalTypeMappingSource typeMappingSo
             return translated;
         }
 
+        if (declaringType == typeof(DateOnly) && TranslateDateOnly(instance, member) is { } translated2)
+        {
+            return translated2;
+        }
+
         if (member.Name == nameof(DateTime.Date))
         {
             // Note that DateTime.Date returns a DateTime, not a DateOnly (introduced later); so we convert using date_trunc (which returns
@@ -190,13 +195,7 @@ SqlExpression LocalNow()
         return _sqlExpressionFactory.Convert(result, typeof(int));
     }
 
-    /// <summary>
-    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
-    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
-    ///     any release. You should only use it directly in your code with extreme caution and knowing that
-    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
-    /// </summary>
-    public virtual SqlExpression? TranslateDateTimeOffset(SqlExpression instance, MemberInfo member)
+    private SqlExpression? TranslateDateTimeOffset(SqlExpression instance, MemberInfo member)
         => member.Name switch
         {
             // We only support UTC DateTimeOffset, so DateTimeOffset.DateTime is just a matter of converting to timestamp without time zone
@@ -226,6 +225,17 @@ SqlExpression LocalNow()
             _ => null
         };
 
+    private SqlExpression? TranslateDateOnly(SqlExpression? instance, MemberInfo member)
+        => member.Name switch
+        {
+            // We use fragment rather than a DateOnly constant, since 0001-01-01 gets rendered as -infinity by default.
+            // TODO: Set the right type/type mapping after https://github.com/dotnet/efcore/pull/34995 is merged
+            nameof(DateOnly.DayNumber) when instance is not null
+                => _sqlExpressionFactory.Subtract(instance, _sqlExpressionFactory.Fragment("DATE '0001-01-01'")),
+
+            _ => null
+        };
+
     // Various conversion functions translated here (date_part, ::time) exist only for timestamp without time zone, so if we pass in a
     // timestamptz it gets implicitly converted to a local timestamp based on TimeZone; that's the wrong behavior (these conversions are not
     // supposed to be sensitive to TimeZone).

src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlDateTimeMethodTranslator.cs

@@ -67,6 +67,10 @@ private static readonly MethodInfo DateOnly_AddMonths
     private static readonly MethodInfo DateOnly_AddYears
         = typeof(DateOnly).GetRuntimeMethod(nameof(DateOnly.AddYears), [typeof(int)])!;
 
+    private static readonly MethodInfo DateOnly_FromDayNumber
+        = typeof(DateOnly).GetRuntimeMethod(
+            nameof(DateOnly.FromDayNumber), [typeof(int)])!;
+
     private static readonly MethodInfo TimeOnly_FromDateTime
         = typeof(TimeOnly).GetRuntimeMethod(nameof(TimeOnly.FromDateTime), [typeof(DateTime)])!;
 
@@ -226,6 +230,18 @@ public NpgsqlDateTimeMethodTranslator(
             {
                 return _sqlExpressionFactory.MakePostgresBinary(PgExpressionType.Distance, arguments[1], arguments[2]);
             }
+
+            if (method == DateOnly_FromDayNumber)
+            {
+                // We use fragment rather than a DateOnly constant, since 0001-01-01 gets rendered as -infinity by default.
+                // TODO: Set the right type/type mapping after https://github.com/dotnet/efcore/pull/34995 is merged
+                return new SqlBinaryExpression(
+                    ExpressionType.Add,
+                    _sqlExpressionFactory.Fragment("DATE '0001-01-01'"),
+                    arguments[0],
+                    typeof(DateOnly),
+                    _typeMappingSource.FindMapping(typeof(DateOnly)));
+            }
         }
         else
         {

src/EFCore.PG/Query/Internal/NpgsqlSqlTranslatingExpressionVisitor.cs

@@ -218,21 +218,39 @@ when binaryExpression.Left.Type.UnwrapNullableType().FullName == "NodaTime.Local
 
         var translation = base.VisitBinary(binaryExpression);
 
-        // A somewhat hacky workaround for #2942.
-        // When an optional owned JSON entity is compared to null, we get WHERE (x -> y) IS NULL.
-        // The -> operator (returning jsonb) is used rather than ->> (returning text), since an entity type is being extracted, and further
-        // JSON operations may need to be composed. However, when the value extracted is a JSON null, a non-NULL jsonb value is returned,
-        // and comparing that to relational NULL returns false.
-        // Pattern-match this and force the use of ->> by changing the mapping to be a scalar rather than an entity type.
-        if (translation is SqlUnaryExpression
+        switch (translation)
+        {
+            // Optimize (x - c) - (y - c) to x - y.
+            // This is particularly useful for DateOnly.DayNumber - DateOnly.DayNumber, which is the way to express DateOnly subtraction
+            // (the subtraction operator isn't defined over DateOnly in .NET). The translation of x.DayNumber is x - DATE '0001-01-01',
+            // so the below is a useful simplification.
+            // TODO: As this is a generic mathematical simplification, we should move it to a generic optimization phase in EF Core.
+            case SqlBinaryExpression
+            {
+                OperatorType: ExpressionType.Subtract,
+                Left: SqlBinaryExpression { OperatorType: ExpressionType.Subtract, Left: var left1, Right: var right1 },
+                Right: SqlBinaryExpression { OperatorType: ExpressionType.Subtract, Left: var left2, Right: var right2 }
+            } originalBinary when right1.Equals(right2):
+            {
+                return new SqlBinaryExpression(ExpressionType.Subtract, left1, left2, originalBinary.Type, originalBinary.TypeMapping);
+            }
+
+            // A somewhat hacky workaround for #2942.
+            // When an optional owned JSON entity is compared to null, we get WHERE (x -> y) IS NULL.
+            // The -> operator (returning jsonb) is used rather than ->> (returning text), since an entity type is being extracted, and
+            // further JSON operations may need to be composed. However, when the value extracted is a JSON null, a non-NULL jsonb value is
+            // returned, and comparing that to relational NULL returns false.
+            // Pattern-match this and force the use of ->> by changing the mapping to be a scalar rather than an entity type.
+            case SqlUnaryExpression
             {
                 OperatorType: ExpressionType.Equal or ExpressionType.NotEqual,
                 Operand: JsonScalarExpression { TypeMapping: NpgsqlOwnedJsonTypeMapping } operand
-            } unary)
-        {
-            return unary.Update(
-                new JsonScalarExpression(
-                    operand.Json, operand.Path, operand.Type, _typeMappingSource.FindMapping("text"), operand.IsNullable));
+            } unary:
+            {
+                return unary.Update(
+                    new JsonScalarExpression(
+                        operand.Json, operand.Path, operand.Type, _typeMappingSource.FindMapping("text"), operand.IsNullable));
+            }
         }
 
         return translation;

src/EFCore.PG/Query/NpgsqlSqlExpressionFactory.cs

@@ -476,6 +476,18 @@ private SqlBinaryExpression ApplyTypeMappingOnSqlBinary(SqlBinaryExpression bina
                     binary.Type,
                     typeMapping ?? _typeMappingSource.FindMapping(binary.Type, "interval"));
             }
+
+            // TODO: This is a hack until https://github.com/dotnet/efcore/pull/34995 is done; the translation of DateOnly.DayNumber
+            // generates a substraction with a fragment, but for now we can't assign a type/type mapping to a fragment.
+            case ExpressionType.Subtract when left.Type == typeof(DateOnly) && right is SqlFragmentExpression:
+            {
+                return new SqlBinaryExpression(
+                    ExpressionType.Subtract,
+                    ApplyDefaultTypeMapping(left),
+                    right,
+                    typeof(int),
+                    _typeMappingSource.FindMapping(typeof(int)));
+            }
         }
 
         // If this is a row value comparison (e.g. (a, b) > (5, 6)), doing type mapping inference on each corresponding pair.

test/EFCore.PG.FunctionalTests/Query/TimestampQueryTest.cs

@@ -744,6 +744,56 @@ WHERE CAST(e."TimestamptzDateTime" AT TIME ZONE 'UTC' AS date) + TIME '15:26:38'
 """);
     }
 
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual async Task DateOnly_DayNumber(bool async)
+    {
+        await AssertQuery(
+            async,
+            ss => ss.Set<Entity>().Where(e => DateOnly.FromDateTime(e.TimestamptzDateTime).DayNumber == 729490));
+
+        AssertSql(
+            """
+SELECT e."Id", e."TimestampDateTime", e."TimestampDateTimeArray", e."TimestampDateTimeOffset", e."TimestampDateTimeOffsetArray", e."TimestampDateTimeRange", e."TimestamptzDateTime", e."TimestamptzDateTimeArray", e."TimestamptzDateTimeRange"
+FROM "Entities" AS e
+WHERE CAST(e."TimestamptzDateTime" AT TIME ZONE 'UTC' AS date) - DATE '0001-01-01' = 729490
+""");
+    }
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual async Task DateOnly_DayNumber_subtraction(bool async)
+    {
+        await AssertQuery(
+            async,
+            ss => ss.Set<Entity>().Where(
+                e => DateOnly.FromDateTime(e.TimestamptzDateTime).DayNumber -
+                    DateOnly.FromDateTime(e.TimestamptzDateTime - TimeSpan.FromDays(3)).DayNumber == 3));
+
+        AssertSql(
+            """
+SELECT e."Id", e."TimestampDateTime", e."TimestampDateTimeArray", e."TimestampDateTimeOffset", e."TimestampDateTimeOffsetArray", e."TimestampDateTimeRange", e."TimestamptzDateTime", e."TimestamptzDateTimeArray", e."TimestamptzDateTimeRange"
+FROM "Entities" AS e
+WHERE CAST(e."TimestamptzDateTime" AT TIME ZONE 'UTC' AS date) - CAST((e."TimestamptzDateTime" - INTERVAL '3 00:00:00') AT TIME ZONE 'UTC' AS date) = 3
+""");
+    }
+
+    [ConditionalTheory]
+    [MemberData(nameof(IsAsyncData))]
+    public virtual async Task DateOnly_FromDayNumber(bool async)
+    {
+        await AssertQuery(
+            async,
+            ss => ss.Set<Entity>().Where(e => DateOnly.FromDayNumber(e.Id) == new DateOnly(0001, 01, 03)));
+
+        AssertSql(
+            """
+SELECT e."Id", e."TimestampDateTime", e."TimestampDateTimeArray", e."TimestampDateTimeOffset", e."TimestampDateTimeOffsetArray", e."TimestampDateTimeRange", e."TimestamptzDateTime", e."TimestamptzDateTimeArray", e."TimestamptzDateTimeRange"
+FROM "Entities" AS e
+WHERE DATE '0001-01-01' + e."Id" = DATE '0001-01-03'
+""");
+    }
+
     #endregion DateOnly
 
     #region TimeOnly