From 49b74fc985e291af379907c9720b9f9ea0536396 Mon Sep 17 00:00:00 2001
From: "Dailey, Alaric" <alaricd@pengdows.com>
Date: Sat, 24 Oct 2026 08:02:24 -0500
Subject: [PATCH] Prioritize custom handlers over type maps

---
 Dapper/SqlMapper.cs                         |  8 ++--
 Directory.Packages.props                    |  1 +
 tests/Dapper.Tests/Dapper.Tests.csproj      |  1 +
 tests/Dapper.Tests/FakeDbTests.Issue1298.cs | 46 +++++++++++++++++++++
 4 files changed, 52 insertions(+), 4 deletions(-)
 create mode 100644 tests/Dapper.Tests/FakeDbTests.Issue1298.cs

diff --git a/Dapper/SqlMapper.cs b/Dapper/SqlMapper.cs
index 8f3956cab..2297e31d4 100644
--- a/Dapper/SqlMapper.cs
+++ b/Dapper/SqlMapper.cs
@@ -473,6 +473,10 @@ public static void SetDbType(IDataParameter parameter, object value)
                 }
                 type = Enum.GetUnderlyingType(type);
             }
+            if (typeHandlers.TryGetValue(type, out handler))
+            {
+                return DbType.Object;
+            }
             if (typeMap.TryGetValue(type, out var mapEntry))
             {
                 if ((mapEntry.Flags & TypeMapEntryFlags.SetType) == 0)
@@ -485,10 +489,6 @@ public static void SetDbType(IDataParameter parameter, object value)
             {
                 return DbType.Binary;
             }
-            if (typeHandlers.TryGetValue(type, out handler))
-            {
-                return DbType.Object;
-            }
             if (typeof(IEnumerable).IsAssignableFrom(type))
             {
                 // auto-detect things like IEnumerable<SqlDataRecord> as a family
diff --git a/Directory.Packages.props b/Directory.Packages.props
index 2f91a3cca..b1e42ba41 100644
--- a/Directory.Packages.props
+++ b/Directory.Packages.props
@@ -38,6 +38,7 @@
     <PackageVersion Include="RepoDb.SqlServer" Version="1.13.1" />
     <PackageVersion Include="ServiceStack.OrmLite.SqlServer" Version="10.0.6" />
     <PackageVersion Include="Snowflake.Data" Version="5.5.0" />
+    <PackageVersion Include="pengdows.crud.fakeDb" Version="2.0.5" />
     <PackageVersion Include="SqlMarshal" Version="0.5.0" />
     <PackageVersion Include="SubSonic" Version="3.0.0.4" />
     <PackageVersion Include="Susanoo.SqlServer" Version="1.2.4.2" />
diff --git a/tests/Dapper.Tests/Dapper.Tests.csproj b/tests/Dapper.Tests/Dapper.Tests.csproj
index 93b498618..e9eab6b88 100644
--- a/tests/Dapper.Tests/Dapper.Tests.csproj
+++ b/tests/Dapper.Tests/Dapper.Tests.csproj
@@ -32,6 +32,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' != 'net481'">
+    <PackageReference Include="pengdows.crud.fakeDb" />
     <PackageReference Include="Npgsql" />
     <PackageReference Include="Snowflake.Data" />
   </ItemGroup>
diff --git a/tests/Dapper.Tests/FakeDbTests.Issue1298.cs b/tests/Dapper.Tests/FakeDbTests.Issue1298.cs
new file mode 100644
index 000000000..5333629c0
--- /dev/null
+++ b/tests/Dapper.Tests/FakeDbTests.Issue1298.cs
@@ -0,0 +1,46 @@
+#if !NET481
+using System.Data;
+using pengdows.crud.fakeDb;
+using Xunit;
+
+namespace Dapper.Tests;
+
+public sealed class FakeDbIssue1298Tests
+{
+    [Fact]
+    public void CustomHandlerOverridesBuiltInTypeMap()
+    {
+        SqlMapper.ResetTypeHandlers();
+        var handler = new StringHandler();
+        SqlMapper.AddTypeHandler(handler);
+        try
+        {
+            using var connection = new fakeDbConnection(new FakeDataStore());
+            connection.EnqueueNonQueryResult(1);
+            connection.Open();
+
+            connection.Execute("select @value", new { value = "hello" });
+
+            Assert.True(handler.Called);
+        }
+        finally
+        {
+            SqlMapper.ResetTypeHandlers();
+        }
+    }
+
+    private sealed class StringHandler : SqlMapper.TypeHandler<string>
+    {
+        public bool Called { get; private set; }
+
+        public override string Parse(object value) => (string)value;
+
+        public override void SetValue(IDbDataParameter parameter, string? value)
+        {
+            Called = true;
+            parameter.DbType = DbType.String;
+            parameter.Value = value;
+        }
+    }
+}
+#endif