Support field access in AccessMultipleMembers; add test

Enhanced AccessMultipleMembers to handle both properties and fields when traversing member names, improving flexibility and robustness. Added a unit test to verify correct OData filter generation when using constant object properties in expressions.

Author: joadan

src/Linq2OData.Core/Expressions/FilterExpressionVisitor.cs

@@ -623,18 +623,24 @@ private static string GetODataMemberName(MemberInfo member)
         {
             foreach (var accessName in memberAccessNames)
             {
-                var property = value.GetType().GetProperty(accessName);
-                if (property == null)
+                var type = value.GetType();
+                var property = type.GetProperty(accessName);
+                if (property != null)
                 {
-                    throw new NotSupportedException($"Property '{accessName}' not found on type '{value.GetType().Name}'");
+                    var nextValue = property.GetValue(value);
+                    if (nextValue == null) return null;
+                    value = nextValue;
                 }
-
-                var nextValue = property.GetValue(value);
-                if (nextValue == null)
+                else
                 {
-                    return null;
+                    var field = type.GetField(accessName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
+                    if (field == null)
+                        throw new NotSupportedException($"Property or field '{accessName}' not found on type '{type.Name}'");
+
+                    var nextValue = field.GetValue(value);
+                    if (nextValue == null) return null;
+                    value = nextValue;
                 }
-                value = nextValue;
             }
             return value;
         }

test/Linq2OData.Tests/FilterExpressionTests.cs

@@ -260,6 +260,24 @@ public void ODataFilterVisitor_GreaterThanOrEqual_GeneratesCorrectFilter()
         Assert.Equal("(Stock ge 10)", result);
     }
 
+    [Fact]
+    public void ODataFilterVisitor_ConstantAsObject_GeneratesCorrectFilter()
+    {
+
+        var product = new TestProduct { ID = 10, Name = "Test", Price = 9.99m, Stock = 100, IsAvailable = true, CreatedDate = DateTime.Now, LastModified = DateTimeOffset.Now, OpenTime = TimeOnly.FromTimeSpan(TimeSpan.FromHours(9)), OpenDate = DateOnly.FromDateTime(DateTime.Today) };
+
+        // Arrange
+        var visitor = new ODataFilterVisitor();
+        Expression<Func<TestProduct, bool>> expression = p => p.Stock >= product.ID;
+
+        // Act
+        var result = visitor.ToFilter(expression, ODataVersion.V4);
+
+        // Assert
+        Assert.Equal("(Stock ge 10)", result);
+    }
+
+
     #endregion
 
     #region Boolean Tests