diff --git a/Src/Asp.NetCore2/MongoDbTest/UnitTest/QuerySelect.cs b/Src/Asp.NetCore2/MongoDbTest/UnitTest/QuerySelect.cs
index 75ff3ec8c..b5a819f2a 100644
--- a/Src/Asp.NetCore2/MongoDbTest/UnitTest/QuerySelect.cs
+++ b/Src/Asp.NetCore2/MongoDbTest/UnitTest/QuerySelect.cs
@@ -179,13 +179,13 @@ namespace MongoDbTest
            }).ToList();
             if (list19.Max(it => it.name) != true) Cases.ThrowUnitError();
 
-            //var list20 = db.Queryable<Student>()
-            //  .Select(it => new
-            //  {
-            //      name = string.IsNullOrEmpty(it.Name).ToString(),
-            //  }).ToList();
-            //if (list20.Max(it => it.name) != "true") Cases.ThrowUnitError();
-             
+            var list20 = db.Queryable<Student>()
+              .Select(it => new
+              {
+                  name = string.IsNullOrEmpty(it.Name).ToString(),
+              }).ToList();
+            if (list20.Max(it => it.name) != "true") Cases.ThrowUnitError();
+
             var list22= db.Queryable<Student>()
             .Select(it=>it.Name).ToList();
             if (list22.First() != "a") Cases.ThrowUnitError();
diff --git a/Src/Asp.NetCore2/SqlSugar.MongoDbCore/MongoDb/SqlBuilder/MongoDbExpressionContext.cs b/Src/Asp.NetCore2/SqlSugar.MongoDbCore/MongoDb/SqlBuilder/MongoDbExpressionContext.cs
index 8b1fcb634..4f1289171 100644
--- a/Src/Asp.NetCore2/SqlSugar.MongoDbCore/MongoDb/SqlBuilder/MongoDbExpressionContext.cs
+++ b/Src/Asp.NetCore2/SqlSugar.MongoDbCore/MongoDb/SqlBuilder/MongoDbExpressionContext.cs
@@ -448,7 +448,7 @@ namespace SqlSugar.MongoDb
             if (model.Args == null || model.Args.Count == 0)
             {
                 // 只有 ToString()，直接转字符串
-                var toStringDoc = new BsonDocument("$toString", $"${memberName}");
+                var toStringDoc = new BsonDocument("$toString", GetMemberName(memberName));
                 return toStringDoc.ToJson(UtilMethods.GetJsonWriterSettings());
             }
             else if (model.Args.Count == 1)
@@ -596,9 +596,14 @@ namespace SqlSugar.MongoDb
             return trimDoc.ToJson(UtilMethods.GetJsonWriterSettings());
         }
 
-        #region  Helper
-
-        // Existing methods...
+        #region  Helper 
+        private static BsonValue GetMemberName(BsonValue memberName)
+        {
+            if (memberName is BsonDocument)
+                return memberName;
+            else
+                return $"${memberName}";
+        }
 
         /// <summary>
         /// Converts a C# date format string to a MongoDB-compatible date format string.