Fix object deserialization when type is not assignable

Author: lbnascimento

LiteDB.Tests/Mapper/Mapper_Tests.cs

@@ -1,4 +1,6 @@
 using FluentAssertions;
+using System;
+using System.Reflection;
 using Xunit;
 
 namespace LiteDB.Tests.Mapper
@@ -17,5 +19,33 @@ public void ToDocument_ReturnsNull_WhenFail()
             var doc2 = _mapper.ToDocument(typeof(int[]), array);
             doc2.Should<BsonDocument>().Be(null);
         }
+
+        [Fact]
+        public void Class_Not_Assignable()
+        {
+            using (var db = new LiteDatabase(":memory:"))
+            {
+                var col = db.GetCollection<MyClass>("Test");
+                col.Insert(new MyClass { Id = 1, Member = null });
+                var type = typeof(OtherClass);
+                var typeName = type.FullName + ", " + type.GetTypeInfo().Assembly.GetName().Name;
+
+                db.Execute($"update Test set Member = {{_id: 1, Name: null, _type: \"{typeName}\"}} where _id = 1");
+
+                Func<MyClass> func = (() => col.FindById(1));
+                func.Should().Throw<LiteException>();
+            }
+        }
+
+        public class MyClass
+        {
+            public int Id { get; set; }
+            public MyClass Member { get; set; }
+        }
+
+        public class OtherClass
+        {
+            public string Name { get; set; }
+        }
     }
 }

LiteDB/Client/Mapper/BsonMapper.Deserialize.cs

@@ -167,9 +167,12 @@ public object Deserialize(Type type, BsonValue value)
                 // test if value is object and has _type
                 if (doc.TryGetValue("_type", out var typeField) && typeField.IsString)
                 {
-                    type = _typeNameBinder.GetType(typeField.AsString);
+                    var actualType = _typeNameBinder.GetType(typeField.AsString);
 
-                    if (type == null) throw LiteException.InvalidTypedName(typeField.AsString);
+                    if (actualType == null) throw LiteException.InvalidTypedName(typeField.AsString);
+                    if (!type.IsAssignableFrom(actualType)) throw LiteException.DataTypeNotAssignable(type.FullName, actualType.FullName);
+
+                    type = actualType;
                 }
                 // when complex type has no definition (== typeof(object)) use Dictionary<string, object> to better set values
                 else if (type == typeof(object))

LiteDB/Utils/LiteException.cs

@@ -51,6 +51,7 @@ public class LiteException : Exception
         public const int INVALID_INITIALSIZE = 211;
         public const int INVALID_NULL_CHAR_STRING = 212;
         public const int INVALID_FREE_SPACE_PAGE = 213;
+        public const int DATA_TYPE_NOT_ASSIGNABLE = 214;
 
         #endregion
 
@@ -306,6 +307,11 @@ internal static LiteException InvalidFreeSpacePage(uint pageID, int freeBytes, i
             return new LiteException(INVALID_FREE_SPACE_PAGE, $"An operation that would corrupt page {pageID} was prevented. The operation required {length} free bytes, but the page had only {freeBytes} available.");
         }
 
+        internal static LiteException DataTypeNotAssignable(string type1, string type2)
+        {
+            return new LiteException(DATA_TYPE_NOT_ASSIGNABLE, $"Data type {type1} is not assignable from data type {type2}");
+        }
+
         #endregion
     }
 }