From b3868f21fd2b8e4c02314e5043becb3948066536 Mon Sep 17 00:00:00 2001
From: JKamsker <jonas@kamsker.at>
Date: Tue, 20 Feb 2024 22:19:07 +0100
Subject: [PATCH] Fix issue: Id is null when anon. type is de/-serialized

---
 LiteDB.Tests/Document/Bson_Tests.cs           | 25 ++++++++++++++++++-
 .../Client/Mapper/BsonMapper.Deserialize.cs   |  8 +++++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/LiteDB.Tests/Document/Bson_Tests.cs b/LiteDB.Tests/Document/Bson_Tests.cs
index fa8085dd7..c8b464caa 100644
--- a/LiteDB.Tests/Document/Bson_Tests.cs
+++ b/LiteDB.Tests/Document/Bson_Tests.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using FluentAssertions;
 using Xunit;
@@ -115,5 +115,28 @@ public void Bson_Partial_Deserialize()
 
             doc4.ToString().Should().Be(src.ToString());
         }
+
+        [Fact]
+        public void BsonMapper_AnonymousType()
+        {
+            var mapper = new BsonMapper();
+
+            var obj = new
+            {
+                Id = 1,
+                Name = "John"
+            };
+
+            var doc = mapper.ToDocument(obj);
+            var obj2 = DeserializeAnonymous(mapper, doc, obj);
+
+            Assert.Equal(obj.Id, obj2.Id);
+            Assert.Equal(obj.Name, obj2.Name);
+
+            static T DeserializeAnonymous<T>(BsonMapper mapper, BsonDocument doc, T obj)
+            {
+                return mapper.Deserialize<T>(doc);
+            }
+        }
     }
 }
\ No newline at end of file
diff --git a/LiteDB/Client/Mapper/BsonMapper.Deserialize.cs b/LiteDB/Client/Mapper/BsonMapper.Deserialize.cs
index 0f3e6259e..3b24d4b2c 100644
--- a/LiteDB/Client/Mapper/BsonMapper.Deserialize.cs
+++ b/LiteDB/Client/Mapper/BsonMapper.Deserialize.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Linq;
 using System.Collections;
 using System.Collections.Generic;
@@ -309,6 +309,12 @@ private object DeserializeAnonymousType(Type type, BsonDocument value)
             {
                 var arg = this.Deserialize(par.ParameterType, value[par.Name]);
 
+                //  if name is Id and arg is null, look for _id
+                if (arg == null && StringComparer.OrdinalIgnoreCase.Equals(par.Name, "Id") && value.TryGetValue("_id", out var id))
+                {
+                    arg = this.Deserialize(par.ParameterType, id);
+                }
+
                 args.Add(arg);
             }