Add support for ValueTypes that consist only of Fields

Author: JKamsker

LiteDB.Tests/Issues/Issue2570_Tests.cs

@@ -0,0 +1,63 @@
+using FluentAssertions;
+using Xunit;
+
+namespace LiteDB.Tests.Issues;
+
+public class Issue2570_Tests
+{
+    public class Person
+    {
+        public int Id { get; set; }
+
+        public (string FirstName, string LastName) Name { get; set; }
+    }
+
+    [Fact]
+    public void Issue2570_Tuples()
+    {
+        using (var db = new LiteDatabase(":memory:"))
+        {
+            var col = db.GetCollection<Person>("Person");
+
+            col.Insert(new Person { Name = ("John", "Doe") });
+            col.Insert(new Person { Name = ("Joana", "Doe") });
+            
+            var result = col.FindOne(x => x.Name.FirstName == "John");
+
+            result.Should().NotBeNull();
+            result.Name.FirstName.Should().Be("John");
+            result.Name.LastName.Should().Be("Doe");
+        }
+    }
+    
+    public struct PersonData
+    {
+        public string FirstName;
+        public string LastName;
+    }
+    
+    public class PersonWithStruct
+    {
+        public int Id { get; set; }
+
+        public PersonData Name { get; set; }
+    }
+    
+    [Fact]
+    public void Issue2570_Structs()
+    {
+        using (var db = new LiteDatabase(":memory:"))
+        {
+            var col = db.GetCollection<PersonWithStruct>("Person");
+
+            col.Insert(new PersonWithStruct { Name = new PersonData { FirstName = "John", LastName = "Doe" } });
+            col.Insert(new PersonWithStruct { Name = new PersonData { FirstName = "Joana", LastName = "Doe" } });
+            
+            var result = col.FindOne(x => x.Name.FirstName == "John");
+
+            result.Should().NotBeNull();
+            result.Name.FirstName.Should().Be("John");
+            result.Name.LastName.Should().Be("Doe");
+        }
+    }
+}

LiteDB/Client/Mapper/BsonMapper.GetEntityMapper.cs

@@ -153,7 +153,10 @@ protected virtual IEnumerable<MemberInfo> GetTypeMembers(Type type)
             .Where(x => x.CanRead && x.GetIndexParameters().Length == 0)
             .Select(x => x as MemberInfo));
 
-        if (this.IncludeFields)
+        var shouldIncludeFields = members.Count == 0
+                                  && type.GetTypeInfo().IsValueType;
+                                  
+        if (shouldIncludeFields || this.IncludeFields)
         {
             members.AddRange(type.GetFields(flags).Where(x => !x.Name.EndsWith("k__BackingField") && x.IsStatic == false)
                 .Select(x => x as MemberInfo));