From 86538d271425c60218084d88a340f69496ff5fc6 Mon Sep 17 00:00:00 2001
From: "Leandro M. Medeiros" <leandro.m.medeiros@me.com>
Date: Fri, 25 Sep 2026 12:16:15 +0200
Subject: [PATCH] fix: Regression - Broken mapping of numeric arrays in
 Postgres (#2231 & #2234)
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The DateOnly/TimeOnly conversion changes introduced in `6d48ef6` excluded `TypeCode.Object` from Dapper’s direct conversion path. As a result, provider-returned PostgreSQL arrays, such as `long[]`, could fall through to `Convert.ChangeType`, breaking mappings to compatible collection types such as `IReadOnlyCollection<long>`.

This change preserves the new DateOnly/TimeOnly conversion behavior while restoring direct assignment when the provider value is assignable to the target type.

A PostgreSQL regression test has also been added covering `bigint|int|smallint[]` to `IReadOnlyCollection<long|int|short>` mapping.

Fixes #2231 and #2234
---
 Dapper/SqlMapper.cs                           |  8 ++++--
 .../Dapper.Tests/Providers/PostgresqlTests.cs | 25 ++++++++++++++++++-
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Dapper/SqlMapper.cs b/Dapper/SqlMapper.cs
index 8f3956cab..4ee8c0587 100644
--- a/Dapper/SqlMapper.cs
+++ b/Dapper/SqlMapper.cs
@@ -3851,13 +3851,17 @@ private static void LoadReaderValueOrBranchToDBNullLabel(ILGenerator il, int ind
                 {
                     TypeCode dataTypeCode = Type.GetTypeCode(colType), unboxTypeCode = Type.GetTypeCode(unboxType);
                     bool hasTypeHandler;
+                    bool providerValueIsAssignable = unboxType.IsAssignableFrom(colType);
                     // note the TypeCode tests are only meaningful for distinct codes: TypeCode.Object
                     // matching TypeCode.Object says nothing (TimeSpan vs TimeOnly?, say), and a direct
                     // unbox there throws; such pairs belong to the flexible-convert path below. A column
                     // reported as plain *object* (sql_variant etc) keeps the direct unbox: the runtime
                     // box is the only truth available there
-                    if ((hasTypeHandler = typeHandlers.ContainsKey(unboxType)) || colType == unboxType
-                        || colType == typeof(object) || unboxType == typeof(object)
+                    if ((hasTypeHandler = typeHandlers.ContainsKey(unboxType))
+                        || colType == unboxType
+                        || providerValueIsAssignable
+                        || colType == typeof(object)
+                        || unboxType == typeof(object)
                         || (dataTypeCode == unboxTypeCode && dataTypeCode != TypeCode.Object)
                         || (dataTypeCode == Type.GetTypeCode(nullUnderlyingType) && dataTypeCode != TypeCode.Object)
                         || colType == nullUnderlyingType)
diff --git a/tests/Dapper.Tests/Providers/PostgresqlTests.cs b/tests/Dapper.Tests/Providers/PostgresqlTests.cs
index b9d60f389..77c229075 100644
--- a/tests/Dapper.Tests/Providers/PostgresqlTests.cs
+++ b/tests/Dapper.Tests/Providers/PostgresqlTests.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Data;
 using System.Data.Common;
 using System.Linq;
 using Xunit;
@@ -68,6 +67,30 @@ private class DateReadings
             public DateOnly AsDateOnly { get; set; }
             public DateTime? AsNullableDateTime { get; set; }
         }
+        
+        private sealed record NumericArraysTable
+        {
+            public IReadOnlyCollection<long> Longs { get; set; } = [];
+            public IReadOnlyCollection<int> Ints { get; set; } = [];
+            public IReadOnlyCollection<short> Shorts { get; set; } = [];
+        }
+
+        [FactPostgresql]
+        public void TestPostgresqlBigintArrayMapsToReadOnlyCollection()
+        {
+            using var conn = GetOpenNpgsqlConnection();
+
+            var row = conn.QuerySingle<NumericArraysTable>(
+                @"SELECT
+                        ARRAY[1001, 1002, 1003]::bigint[]   AS ""Longs""
+                      , ARRAY[2001, 2002, 2003]::int[]      AS ""Ints""
+                      , ARRAY[3001, 3002, 3003]::smallint[] AS ""Shorts""
+                    ;");
+
+            Assert.Equal(new [] { 1001L, 1002L, 1003L }, row.Longs.ToArray());
+            Assert.Equal(new [] { 2001, 2002, 2003 }, row.Ints.ToArray());
+            Assert.Equal(new short[] { 3001, 3002, 3003 }, row.Shorts.ToArray());
+        }
 #endif
 
         [FactPostgresql]