From fe82ce079912ec1eac64ba02cab34a5b8f4c5eec Mon Sep 17 00:00:00 2001
From: DocSvartz <svartzdoctor@gmail.com>
Date: Wed, 8 Apr 2026 17:51:20 +0500
Subject: [PATCH] feat: add Flattening mapping for all source type only
 primitive

---
 src/Mapster.Tests/WhenFlattening.cs           | 33 +++++++++++++++++--
 .../Settings/ValueAccessingStrategy.cs        |  3 +-
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/src/Mapster.Tests/WhenFlattening.cs b/src/Mapster.Tests/WhenFlattening.cs
index da7f64d9..a823a9a6 100644
--- a/src/Mapster.Tests/WhenFlattening.cs
+++ b/src/Mapster.Tests/WhenFlattening.cs
@@ -1,6 +1,7 @@
-using System;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Shouldly;
+using System;
+using System.Collections.Generic;
 using Assert = Microsoft.VisualStudio.TestTools.UnitTesting.Assert;
 
 namespace Mapster.Tests
@@ -78,12 +79,40 @@ public class ModelDto
         public string SubSubSubCoolProperty { get; set; }
     }
 
+    public class Source915
+    {
+        public ICollection<Case> Cases { get; set; } = new List<Case>
+        {
+            new Case(),
+            new Case(),
+            new Case()
+        };
+    }
+
+    public class Destination915
+    {
+        public int CasesCount { get; set; }
+    }
 
     #endregion
 
+
     [TestClass]
     public class WhenFlattening
     {
+
+        /// <summary>
+        /// https://github.com/MapsterMapper/Mapster/issues/915
+        /// </summary>
+        [TestMethod]
+        public void FlatteningUsingSourceInterface()
+        {
+            var source = new Source915();
+            var result = source.Adapt<Destination915>();
+
+            result.CasesCount.ShouldBe(source.Cases.Count);
+        }
+
         [TestMethod]
         public void GetMethodTest()
         {
diff --git a/src/Mapster/Settings/ValueAccessingStrategy.cs b/src/Mapster/Settings/ValueAccessingStrategy.cs
index fd13407d..f43f5ff3 100644
--- a/src/Mapster/Settings/ValueAccessingStrategy.cs
+++ b/src/Mapster/Settings/ValueAccessingStrategy.cs
@@ -116,8 +116,7 @@ public static class ValueAccessingStrategy
                     return member.GetExpression(source);
 
                 var propertyType = member.Type;
-                if (propertyName.StartsWith(sourceMemberName) &&
-                    (propertyType.IsPoco() || propertyType.IsRecordType()))
+                if (propertyName.StartsWith(sourceMemberName) && !propertyType.IsMapsterPrimitive())
                 {
                     var exp = member.GetExpression(source);
                     var ifTrue = GetDeepFlattening(exp, propertyName.Substring(sourceMemberName.Length).TrimStart('_'), arg);