fix duplicate join issues (#993)

* fix duplicate join issues

* update based on review comments

* remove white space

* update changes

* update changes

* update based on review comments

Author: ElizabethOkerio

src/Microsoft.AspNetCore.OData/Microsoft.AspNetCore.OData.xml

@@ -9624,6 +9624,11 @@
             Basically for $compute in $select and $expand
             </summary>
         </member>
+        <member name="P:Microsoft.AspNetCore.OData.Query.Expressions.QueryBinderContext.QueryProvider">
+            <summary>
+            Gets or sets the query provider.
+            </summary>
+        </member>
         <member name="M:Microsoft.AspNetCore.OData.Query.Expressions.QueryBinderContext.GetParameter(System.String)">
             <summary>
             Gets the parameter using parameter name.

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

@@ -273,6 +273,11 @@ public static IQueryable ApplyBind(this ISelectExpandBinder binder, IQueryable s
                 throw Error.ArgumentNull(nameof(context));
             }
 
+            if (string.IsNullOrEmpty(context.QueryProvider))
+            {
+                context.QueryProvider = source.Provider.GetType().Namespace;
+            }
+
             Type elementType = context.ElementClrType;
 
             LambdaExpression projectionLambda = binder.BindSelectExpand(selectExpandClause, context) as LambdaExpression;

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

@@ -100,6 +100,8 @@ public QueryBinderContext(QueryBinderContext context, ODataQuerySettings querySe
 
             ElementType = Model.GetEdmTypeReference(ElementClrType)?.Definition;
 
+            QueryProvider = context.QueryProvider;
+
             if (ElementType == null)
             {
                 throw new ODataException(Error.Format(SRResources.ClrTypeNotInModel, ElementClrType.FullName));
@@ -168,6 +170,11 @@ public QueryBinderContext(QueryBinderContext context, ODataQuerySettings querySe
         /// </summary>
         public Expression Source { get;set; }
 
+        /// <summary>
+        /// Gets or sets the query provider.
+        /// </summary>
+        internal string QueryProvider { get; set; }
+
         /// <summary>
         /// Gets the parameter using parameter name.
         /// </summary>

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

@@ -368,9 +368,23 @@ internal Expression ProjectElement(QueryBinderContext context, Expression source
             bool isSelectedAll = IsSelectAll(selectExpandClause);
             if (isSelectedAll)
             {
+                // If we have an EF query provider, then we remove the non-structural properties. The reason for this is to avoid 
+                // Creating an expression that will generate duplicate LEFT joins when a LEFT join already exists in the IQueryable 
+                // as observed here: https://github.com/OData/AspNetCoreOData/issues/497
+
+                Expression updatedExpression = null;
+                if (IsEfQueryProvider(context))
+                {
+                    updatedExpression = SelectExpandBinder.RemoveNonStructucalProperties(source, structuredType);
+                }
+                else 
+                {
+                    updatedExpression = source;
+                }
+
                 // Initialize property 'Instance' on the wrapper class
                 wrapperProperty = wrapperType.GetProperty("Instance");
-                wrapperTypeMemberAssignments.Add(Expression.Bind(wrapperProperty, source));
+                wrapperTypeMemberAssignments.Add(Expression.Bind(wrapperProperty, updatedExpression));
 
                 wrapperProperty = wrapperType.GetProperty("UseInstanceForProperties");
                 wrapperTypeMemberAssignments.Add(Expression.Bind(wrapperProperty, Expression.Constant(true)));
@@ -427,6 +441,51 @@ internal Expression ProjectElement(QueryBinderContext context, Expression source
             return Expression.MemberInit(Expression.New(wrapperType), wrapperTypeMemberAssignments);
         }
 
+        // Generates the expression
+        //      { Instance = new Customer() {Id = $it.Id, Name= $it.Name}}
+        private static Expression RemoveNonStructucalProperties(Expression source, IEdmStructuredType structuredType)
+        {
+            Expression updatedSource = null;
+
+            Type elementType = source.Type;
+            IEnumerable<IEdmStructuralProperty> structuralProperties = structuredType.StructuralProperties();
+
+            PropertyInfo[] props = elementType.GetProperties();
+            List<MemberBinding> bindings = new List<MemberBinding>();
+
+            foreach (PropertyInfo prop in props)
+            {
+                foreach (var sp in structuralProperties)
+                {
+                    if (sp.Name == prop.Name)
+                    {
+                        MemberExpression propertyExpression = Expression.Property(source, prop);
+                        bindings.Add(Expression.Bind(prop, propertyExpression));
+                        break;
+                    }
+                }
+            }
+
+            NewExpression newExpression = Expression.New(source.Type);
+            updatedSource = Expression.MemberInit(newExpression, bindings);
+
+            return updatedSource;     
+        }
+
+        private bool IsEfQueryProvider(QueryBinderContext context)
+        {
+            if (context.QueryProvider != null &&
+                context.QueryProvider == HandleNullPropagationOptionHelper.EntityFrameworkQueryProviderNamespace ||
+                context.QueryProvider == HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEF5 ||
+                context.QueryProvider == HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEF6 ||
+                context.QueryProvider == HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEFCore2)
+            {
+                return true;
+            }
+
+            return false;
+        }
+
         private static bool ParseComputedDynamicProperties(QueryBinderContext context, IList<DynamicPathSegment> dynamicPathSegments, bool isSelectedAll,
             out IList<string> computedProperties)
         {

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

@@ -13,7 +13,6 @@
 using System.Linq.Expressions;
 using System.Reflection;
 using System.Runtime.Serialization;
-using System.Xml.Linq;
 using Microsoft.AspNetCore.OData.Edm;
 using Microsoft.AspNetCore.OData.Query;
 using Microsoft.AspNetCore.OData.Query.Container;
@@ -209,6 +208,44 @@ public void Bind_GeneratedExpression_ContainsExpandedObject()
             Assert.Same(_queryable.First(), innerInnerCustomer.Instance);
         }
 
+        [Theory]
+        [InlineData(HandleNullPropagationOptionHelper.EntityFrameworkQueryProviderNamespace)]
+        [InlineData(HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEFCore2)]
+        [InlineData(HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEF5)]
+        [InlineData(HandleNullPropagationOptionHelper.ObjectContextQueryProviderNamespaceEF6)]
+        public void Bind_UsingEFQueryProvider_GeneratedExpression__DoesNot_ContainExpandedObject(string queryProvider)
+        {
+            // Arrange
+            SelectExpandQueryOption selectExpand = new SelectExpandQueryOption("Orders", "Orders,Orders($expand=Customer)", _context);
+
+            // Act
+            SelectExpandBinder binder = new SelectExpandBinder();
+            _queryBinderContext.QueryProvider = queryProvider;
+            IQueryable queryable = binder.ApplyBind(_queryable, selectExpand.SelectExpandClause, _queryBinderContext);
+
+            // Assert
+            IEnumerator enumerator = queryable.GetEnumerator();
+            Assert.True(enumerator.MoveNext());
+            var partialCustomer = Assert.IsAssignableFrom<SelectExpandWrapper<QueryCustomer>>(enumerator.Current);
+            Assert.False(enumerator.MoveNext());
+            Assert.Null(partialCustomer.Instance);
+            Assert.Equal("Microsoft.AspNetCore.OData.Tests.Query.Expressions.QueryCustomer", partialCustomer.InstanceType);
+            IEnumerable<SelectExpandWrapper<QueryOrder>> innerOrders = partialCustomer.Container
+                .ToDictionary(PropertyMapper)["Orders"] as IEnumerable<SelectExpandWrapper<QueryOrder>>;
+            Assert.NotNull(innerOrders);
+            SelectExpandWrapper<QueryOrder> partialOrder = innerOrders.Single();
+            
+            // We only write structural properties to the instance.
+            // This means that navigation properties on the instance property will be null
+            // when using any instance of EF query provider. 
+            Assert.Null(partialOrder.Instance.Customer);
+
+            object customer = partialOrder.Container.ToDictionary(PropertyMapper)["Customer"];
+            SelectExpandWrapper<QueryCustomer> innerInnerCustomer = Assert.IsAssignableFrom<SelectExpandWrapper<QueryCustomer>>(customer);
+
+            Assert.Null(innerInnerCustomer.Instance.Orders);
+        }
+
         [Fact]
         public void Bind_GeneratedExpression_CheckNullObjectWithinChainProjectionByKey()
         {