Fix Linq-to-BsonExpression with BsonRef property when it inherits fro…

…m another class

LiteDB.Tests/Issue1651_Tests.cs

@@ -0,0 +1,69 @@
+using System;
+using System.Collections.Generic;
+using Xunit;
+using System.Linq;
+
+namespace LiteDB.Issue1651
+{
+    public class Order : BaseEntity
+    {
+        public Customer Customer { get; set; }
+    }
+
+    public class Customer : BaseEntity
+    {
+        public string Name { get; set; }
+    }
+
+    public class BaseEntity
+    {
+        public Guid Id { get; set; }
+    }
+    public class CustomerRelationshipsTests
+    {
+        [Fact]
+        public void Find_ByRelationId_Success()
+        {
+            BsonMapper.Global.Entity<Order>().DbRef(order => order.Customer);
+
+            using var _database = new LiteDatabase(":memory:");
+            var _orderCollection = _database.GetCollection<Order>("Order");
+            var _customerCollection = _database.GetCollection<Customer>("Customer");
+
+            var customer = new Customer() { Name = "John", };
+
+            Assert.True(_customerCollection.Upsert(customer));
+            Assert.True(_customerCollection.Upsert(new Customer() { Name = "Anonymous" }));
+
+            Assert.NotEqual(Guid.Empty, customer.Id);
+
+            var order = new Order()
+            {
+                Customer = customer,
+            };
+            var order2 = new Order()
+            {
+                Customer = new Customer() { Id = customer.Id },
+            };
+            var orphanOrder = new Order();
+
+            Assert.True(_orderCollection.Upsert(orphanOrder));
+            Assert.True(_orderCollection.Upsert(order));
+            Assert.True(_orderCollection.Upsert(order2));
+
+            customer.Name = "Josh";
+            Assert.True(_customerCollection.Update(customer));
+
+            var actualOrders = _orderCollection
+                .Include(orderEntity => orderEntity.Customer)
+                .Find(orderEntity => orderEntity.Customer.Id == customer.Id)
+                .ToList();
+
+            Assert.Equal(2, actualOrders.Count);
+            Assert.Equal(new[] { customer.Name, customer.Name },
+                actualOrders.Select(actualOrder => actualOrder.Customer.Name));
+            Assert.Equal(2, (_customerCollection.FindAll().ToList()).Count);
+            Assert.Equal(3, (_orderCollection.FindAll().ToList()).Count);
+        }
+    }
+}

LiteDB/Client/Mapper/Linq/LinqExpressionVisitor.cs

@@ -602,7 +602,7 @@ private string ResolveMember(MemberInfo member)
             var name = member.Name;
 
             // checks if parent field are not DbRef (checks for same dataType)
-            var isParentDbRef = _dbRefType != null && _dbRefType == member.DeclaringType;
+            var isParentDbRef = _dbRefType != null && member.DeclaringType.IsAssignableFrom(_dbRefType);
 
             // get class entity from mapper
             var entity = _mapper.GetEntityMapper(member.DeclaringType);