fix: apply custom Map results when mapping to existing target (#900)

src/Mapster.Tests/WhenMappingGetterOnlyMapToTargetRegression.cs

@@ -0,0 +1,75 @@
+using MapsterMapper;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Shouldly;
+
+namespace Mapster.Tests;
+
+/// <summary>
+/// https://github.com/MapsterMapper/Mapster/issues/900
+/// </summary>
+[TestClass]
+public class WhenMappingGetterOnlyMapToTargetRegression
+{
+    [TestMethod]
+    public void MapToTarget_WithCustomMap_ShouldReplaceExistingDestinationMemberValue()
+    {
+        var config = new TypeAdapterConfig();
+        config.NewConfig<Dto900, Entity900>()
+            .Map(x => x.Data, x => x.Data == null ? null : new Data900(x.Data.Value));
+
+        var mapper = new Mapper(config);
+
+        var dto = new Dto900 { Data = new Data900("new") };
+        var entity = mapper.Map(dto, new Entity900 { Data = new Data900("old") });
+
+        entity.Data.ShouldNotBeNull();
+        entity.Data!.Value.ShouldBe("new");
+    }
+
+    [TestMethod]
+    public void MapToTarget_WithCustomMap_ShouldStillWorkWhenDestinationMemberIsNull()
+    {
+        var config = new TypeAdapterConfig();
+        config.NewConfig<Dto900, Entity900>()
+            .Map(x => x.Data, x => x.Data == null ? null : new Data900(x.Data.Value));
+
+        var mapper = new Mapper(config);
+
+        var dto = new Dto900 { Data = new Data900("new") };
+        var entity = mapper.Map(dto, new Entity900());
+
+        entity.Data.ShouldNotBeNull();
+        entity.Data!.Value.ShouldBe("new");
+    }
+
+    [TestMethod]
+    public void Map_WithCustomMap_ShouldStillWorkForNewDestination()
+    {
+        var config = new TypeAdapterConfig();
+        config.NewConfig<Dto900, Entity900>()
+            .Map(x => x.Data, x => x.Data == null ? null : new Data900(x.Data.Value));
+
+        var mapper = new Mapper(config);
+
+        var dto = new Dto900 { Data = new Data900("new") };
+        var entity = mapper.Map<Entity900>(dto);
+
+        entity.Data.ShouldNotBeNull();
+        entity.Data!.Value.ShouldBe("new");
+    }
+
+    private class Dto900
+    {
+        public Data900? Data { get; set; }
+    }
+
+    private class Entity900
+    {
+        public Data900? Data { get; set; }
+    }
+
+    private class Data900(string value)
+    {
+        public string Value => value;
+    }
+}

src/Mapster/Adapters/BaseClassAdapter.cs

@@ -200,6 +200,13 @@ protected static bool IsCanUsingDestinationValue(CompileArgument arg, IMemberMod
             return false;
         }
 
+        protected static bool HasCustomMemberMap(CompileArgument arg, IMemberModel destinationMember)
+        {
+            return arg.Settings.Resolvers.Any(resolver =>
+                !resolver.IsChildPath &&
+                string.Equals(resolver.DestinationMemberName, destinationMember.Name, StringComparison.InvariantCultureIgnoreCase));
+        }
+
         protected static bool ProcessIgnores(
             CompileArgument arg,
             IMemberModel destinationMember,

src/Mapster/Adapters/ClassAdapter.cs

@@ -110,7 +110,8 @@ protected override Expression CreateBlockExpression(Expression source, Expressio
             Dictionary<LambdaExpression, Tuple<List<Expression>, Expression>>? conditions = null;
             foreach (var member in members)
             {
-                var destMember = arg.MapType == MapType.MapToTarget || member.UseDestinationValue
+                var hasCustomMap = HasCustomMemberMap(arg, member.DestinationMember);
+                var destMember = (arg.MapType == MapType.MapToTarget || member.UseDestinationValue) && !hasCustomMap
                     ? member.DestinationMember.GetExpression(destination)
                     : null;