Fix $expand with null properties

Author: ElizabethOkerio

src/Microsoft.AspNetCore.OData/Query/Expressions/SelectExpandBinder.cs

@@ -453,15 +453,44 @@ private static Expression RemoveNonStructucalProperties(QueryBinderContext conte
 
             PropertyInfo[] props = elementType.GetProperties();
             List<MemberBinding> bindings = new List<MemberBinding>();
+            ODataQuerySettings settings = context.QuerySettings;
+            bool isSourceNullable = ExpressionBinderHelper.IsNullable(source.Type);
 
             foreach (PropertyInfo prop in props)
             {
+                bool isPropertyNullable = ExpressionBinderHelper.IsNullable(prop.PropertyType);
+
                 foreach (var sp in structuralProperties)
                 {
                     if (prop.CanWrite && model.GetClrPropertyName(sp) == prop.Name)
                     {
-                        MemberExpression propertyExpression = Expression.Property(source, prop);
-                        bindings.Add(Expression.Bind(prop, propertyExpression));
+                        Expression propertyValue = Expression.Property(source, prop);
+                        Type nullablePropertyType = TypeHelper.ToNullable(propertyValue.Type);
+                        Expression nullablePropertyValue = ExpressionHelpers.ToNullable(propertyValue);
+
+                        if ((settings.HandleNullPropagation == HandleNullPropagationOption.True) || (isSourceNullable && isPropertyNullable))
+                        {
+                            propertyValue = Expression.Condition(
+                                test: Expression.Equal(source, Expression.Constant(value: null)),
+                                ifTrue: Expression.Constant(value: null, type: nullablePropertyType),
+                                ifFalse: nullablePropertyValue);
+                        }
+                        else if (isSourceNullable)
+                        {
+                            object defaultValue = prop.PropertyType.IsValueType ? Activator.CreateInstance(prop.PropertyType) : null;
+                            
+                            // property is non-nullable
+                            propertyValue = Expression.Condition(
+                                test: Expression.Equal(source, Expression.Constant(value: null)),
+                                ifTrue: Expression.Constant(value: defaultValue),
+                                ifFalse: propertyValue);
+                        }
+                        else if (isPropertyNullable)
+                        {
+                            propertyValue = nullablePropertyValue;
+                        }
+
+                        bindings.Add(Expression.Bind(prop, propertyValue));
                         break;
                     }
                 }

test/Microsoft.AspNetCore.OData.Tests/Query/Expressions/SelectExpandBinderTest.cs

@@ -10,6 +10,7 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -36,6 +37,7 @@ public class SelectExpandBinderTest
         private readonly SelectExpandBinder _binder;
         private readonly SelectExpandBinder _binder_lowerCamelCased;
         private readonly IQueryable<QueryCustomer> _queryable;
+        private readonly IQueryable<QueryCustomer> _queryable1;
         private readonly IQueryable<QueryCustomer> _queryable_lowerCamelCased;
         private readonly ODataQueryContext _context;
         private readonly ODataQueryContext _context_lowerCamelCased;
@@ -82,7 +84,19 @@ public SelectExpandBinderTest()
             QueryOrder order = new QueryOrder { Id = 42, Title = "The order", Customer = customer };
             customer.Orders.Add(order);
 
+            QueryCustomer customer1 = new QueryCustomer
+            {
+                Orders = new List<QueryOrder>()
+            };
+
+            QueryOrder order1 = new QueryOrder { Id = 42, Title = "The order", Customer = customer1 };
+            QueryOrder order2 = null;
+
+            customer1.Orders.Add(order1);
+            customer1.Orders.Add(order2);
+
             _queryable = new[] { customer }.AsQueryable();
+            _queryable1 = new[] { customer1 }.AsQueryable();
 
             SelectExpandQueryOption selectExpandQueryOption = new SelectExpandQueryOption("Orders", expand: null, context: _context);
 
@@ -270,7 +284,7 @@ public void Bind_UsingEFQueryProvider_GeneratedExpression__DoesNot_ContainExpand
             // Act
             SelectExpandBinder binder = new SelectExpandBinder();
             _queryBinderContext.QueryProvider = queryProvider;
-            IQueryable queryable = binder.ApplyBind(_queryable, selectExpand.SelectExpandClause, _queryBinderContext);
+            IQueryable queryable = binder.ApplyBind(_queryable1, selectExpand.SelectExpandClause, _queryBinderContext);
 
             // Assert
             IEnumerator enumerator = queryable.GetEnumerator();
@@ -282,7 +296,7 @@ public void Bind_UsingEFQueryProvider_GeneratedExpression__DoesNot_ContainExpand
             IEnumerable<SelectExpandWrapper<QueryOrder>> innerOrders = partialCustomer.Container
                 .ToDictionary(PropertyMapper)["Orders"] as IEnumerable<SelectExpandWrapper<QueryOrder>>;
             Assert.NotNull(innerOrders);
-            SelectExpandWrapper<QueryOrder> partialOrder = innerOrders.Single();
+            SelectExpandWrapper<QueryOrder> partialOrder = innerOrders.FirstOrDefault();
 
             // We only write structural properties to the instance.
             // This means that navigation properties on the instance property will be null
@@ -327,7 +341,7 @@ public void Bind_UsingEFQueryProvider_LowerCamelCasedModel_GeneratedExpression__
             IEnumerable<SelectExpandWrapper<QueryOrder>> innerOrders = partialCustomer.Container
                 .ToDictionary(PropertyMapper)["orders"] as IEnumerable<SelectExpandWrapper<QueryOrder>>;
             Assert.NotNull(innerOrders);
-            SelectExpandWrapper<QueryOrder> partialOrder = innerOrders.Single();
+            SelectExpandWrapper<QueryOrder> partialOrder = innerOrders.FirstOrDefault();
 
             // We only write structural properties to the instance.
             // This means that navigation properties on the instance property will be null
@@ -343,6 +357,52 @@ public void Bind_UsingEFQueryProvider_LowerCamelCasedModel_GeneratedExpression__
             Assert.Null(innerInnerCustomer.Instance.Orders);
         }
 
+        [Fact]
+        public void Bind_SelectAndExpand_WithNullProperties_DoesNotThrowException()
+        {
+            // Arrange
+            IQueryable<User> users;
+            string expand = "FileRefNavigation";
+
+            User user = new User
+            {
+                UserId = 1,
+                Name = "Alex",
+                Age = 35,
+                DataFileRef = null,
+                FileRefNavigation = null
+            };
+
+            users = new[] { user }.AsQueryable();
+            ODataQueryContext context = new ODataQueryContext(_model, typeof(User)) { RequestContainer = new MockServiceProvider() };
+
+            SelectExpandQueryOption selectExpand = new SelectExpandQueryOption(select: null, expand: expand, context: context);
+
+            QueryBinderContext queryBinderContext = new QueryBinderContext(_model, _settings, selectExpand.Context.ElementClrType)
+            {
+                NavigationSource = context.NavigationSource
+            };
+
+            queryBinderContext.QueryProvider = HandleNullPropagationOptionHelper.EntityFrameworkQueryProviderNamespace;
+
+            // Act
+            SelectExpandBinder binder = new SelectExpandBinder();
+            IQueryable queryable = binder.ApplyBind(users, selectExpand.SelectExpandClause, queryBinderContext);
+
+            // Assert
+            Assert.NotNull(queryable);
+
+            IEnumerator enumerator = queryable.GetEnumerator();
+            Assert.True(enumerator.MoveNext());
+            var usr = Assert.IsAssignableFrom<SelectExpandWrapper<User>>(enumerator.Current);
+            Assert.False(enumerator.MoveNext());
+            Assert.NotNull(usr.Instance);
+            Assert.Equal("Microsoft.AspNetCore.OData.Tests.Query.Expressions.User", usr.Instance.GetType().ToString());
+            IEnumerable<SelectExpandWrapper<DataFile>> fileRefsNavigations = usr.Container
+                .ToDictionary(PropertyMapper)["FileRefNavigation"] as IEnumerable<SelectExpandWrapper<DataFile>>;
+            Assert.Null(fileRefsNavigations);
+        }
+
         [Fact]
         public void Bind_GeneratedExpression_CheckNullObjectWithinChainProjectionByKey()
         {
@@ -2082,6 +2142,7 @@ public static IEdmModel GetEdmModel()
             builder.EntitySet<QueryOrder>("Orders");
             builder.EntitySet<QueryCity>("Cities");
             builder.EntitySet<QueryProduct>("Products");
+            builder.EntitySet<User>("Users");
 
             customer.Collection.Function("IsUpgraded").Returns<bool>().Namespace="NS";
             customer.Collection.Action("UpgradeAll").Namespace = "NS";
@@ -2229,9 +2290,9 @@ public class QueryCustomer
 
         public IList<QueryAddress> Addresses { get; set; }
 
-        public QueryOrder PrivateOrder { get; set; }
+        public QueryOrder? PrivateOrder { get; set; }
 
-        public IList<QueryOrder> Orders { get; set; }
+        public IList<QueryOrder>? Orders { get; set; }
 
         public List<string> TestReadonlyProperty
         {
@@ -2292,4 +2353,27 @@ public enum QueryColor
 
         Blue
     }
+
+    public class User
+    {
+        [Key]
+        public int UserId { get; set; }
+        [Required]
+        public string Name { get; set; }
+        [Required]
+        public int Age { get; set; }
+
+        //Navigations
+        [ForeignKey("FileRefNavigation")]
+        public int? DataFileRef { get; set; }
+        public DataFile? FileRefNavigation { get; set; }
+    }
+
+    public class DataFile
+    {
+        [Key]
+        public int FileId { get; set; }
+        [Required]
+        public string FileName { get; set; }
+    }
 }