Query: Map projection properly when joining 2 tables

When joining 2 tables in relational, we lift the table from inner select expression and copy over projections. If one of this projection is same as any outer projection then we reuse the same projection. That means the associated indexes in inner shaper will go to different indexes rather than in linear fashion.
Fix is to remember which index each projection went and use that rather than applying an offset.

Resolves #19616

src/EFCore.Relational/Query/SqlExpressions/SelectExpression.cs

@@ -914,9 +914,11 @@ public Expression ApplyCollectionJoin(
             }
 
             var indexOffset = _projection.Count;
-            foreach (var projection in innerSelectExpression.Projection)
+            var innerProjectionCount = innerSelectExpression.Projection.Count;
+            var indexMap = new int[innerProjectionCount];
+            for (var i = 0; i < innerProjectionCount; i++)
             {
-                AddToProjection(MakeNullable(projection.Expression));
+                indexMap[i] = AddToProjection(MakeNullable(innerSelectExpression.Projection[i].Expression));
             }
 
             foreach (var identifier in innerSelectExpression._identifier.Concat(innerSelectExpression._childIdentifiers))
@@ -926,7 +928,10 @@ public Expression ApplyCollectionJoin(
                 AppendOrdering(new OrderingExpression(updatedColumn, ascending: true));
             }
 
-            var shaperRemapper = new ShaperRemappingExpressionVisitor(this, innerSelectExpression, indexOffset);
+            var shaperRemapper = AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue19616", out var isEnabled)
+                && isEnabled
+                ? new ShaperRemappingExpressionVisitor(this, innerSelectExpression, indexOffset)
+                : new ShaperRemappingExpressionVisitor(this, innerSelectExpression, indexMap);
             innerShaper = shaperRemapper.Visit(innerShaper);
             selfIdentifier = shaperRemapper.Visit(selfIdentifier);
 
@@ -961,21 +966,32 @@ private class ShaperRemappingExpressionVisitor : ExpressionVisitor
             private readonly SelectExpression _queryExpression;
             private readonly SelectExpression _innerSelectExpression;
             private readonly int _offset;
+            private readonly int[] _indexMap;
 
-            public ShaperRemappingExpressionVisitor(SelectExpression queryExpression, SelectExpression innerSelectExpression, int offset)
+            public ShaperRemappingExpressionVisitor(
+                SelectExpression queryExpression, SelectExpression innerSelectExpression, int offset)
             {
                 _queryExpression = queryExpression;
                 _innerSelectExpression = innerSelectExpression;
                 _offset = offset;
             }
 
+            public ShaperRemappingExpressionVisitor(
+                SelectExpression queryExpression, SelectExpression innerSelectExpression, int[] indexMap)
+            {
+                _queryExpression = queryExpression;
+                _innerSelectExpression = innerSelectExpression;
+                _indexMap = indexMap;
+            }
+
             protected override Expression VisitExtension(Expression extensionExpression)
             {
                 if (extensionExpression is ProjectionBindingExpression projectionBindingExpression)
                 {
                     var oldIndex = (int)GetProjectionIndex(projectionBindingExpression);
+                    var newIndex = _indexMap?[oldIndex] ?? oldIndex + _offset;
 
-                    return new ProjectionBindingExpression(_queryExpression, oldIndex + _offset, projectionBindingExpression.Type);
+                    return new ProjectionBindingExpression(_queryExpression, newIndex, projectionBindingExpression.Type);
                 }
 
                 if (extensionExpression is EntityShaperExpression entityShaper)
@@ -985,7 +1001,8 @@ protected override Expression VisitExtension(Expression extensionExpression)
                     var indexMap = new Dictionary<IProperty, int>();
                     foreach (var keyValuePair in oldIndexMap)
                     {
-                        indexMap[keyValuePair.Key] = keyValuePair.Value + _offset;
+                        var oldIndex = keyValuePair.Value;
+                        indexMap[keyValuePair.Key] = _indexMap?[oldIndex] ?? oldIndex + _offset;
                     }
 
                     return new EntityShaperExpression(

test/EFCore.Cosmos.FunctionalTests/Query/SimpleQueryCosmosTest.Select.cs

@@ -921,5 +921,11 @@ public override Task LastOrDefault_member_access_in_projection_translates_to_ser
         {
             return base.LastOrDefault_member_access_in_projection_translates_to_server(isAsync);
         }
+
+        [ConditionalTheory(Skip = "Issue#17246")]
+        public override Task Projecting_multiple_collection_with_same_constant_works(bool async)
+        {
+            return base.Projecting_multiple_collection_with_same_constant_works(async);
+        }
     }
 }

test/EFCore.Specification.Tests/Query/SimpleQueryTestBase.Select.cs

@@ -1492,5 +1492,25 @@ public CustomerWrapper2(Customer customer)
             public string City { get; set; }
             public Customer Customer { get; }
         }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task Projecting_multiple_collection_with_same_constant_works(bool async)
+        {
+            return AssertQuery(
+                async,
+                ss => ss.Set<Customer>().Where(c => c.CustomerID == "ALFKI")
+                    .Select(c => new
+                    {
+                        O1 = c.Orders.Select(e => new { Value = 1 }),
+                        O2 = c.Orders.Select(e => new { AnotherValue = 1 })
+                    }),
+                assertOrder: true, //single element
+                elementAsserter: (e, a) =>
+                {
+                    AssertCollection(e.O1, a.O1, ordered: true);
+                    AssertCollection(e.O2, a.O2, ordered: true);
+                });
+        }
     }
 }

test/EFCore.SqlServer.FunctionalTests/Query/SimpleQuerySqlServerTest.Select.cs

@@ -1227,5 +1227,18 @@ FROM [Orders] AS [o]
 FROM [Customers] AS [c]
 WHERE [c].[CustomerID] LIKE N'A%'");
         }
+
+        public override async Task Projecting_multiple_collection_with_same_constant_works(bool async)
+        {
+            await base.Projecting_multiple_collection_with_same_constant_works(async);
+
+            AssertSql(
+                @"SELECT [c].[CustomerID], 1, [o].[OrderID], [o0].[OrderID]
+FROM [Customers] AS [c]
+LEFT JOIN [Orders] AS [o] ON [c].[CustomerID] = [o].[CustomerID]
+LEFT JOIN [Orders] AS [o0] ON [c].[CustomerID] = [o0].[CustomerID]
+WHERE [c].[CustomerID] = N'ALFKI'
+ORDER BY [c].[CustomerID], [o].[OrderID], [o0].[OrderID]");
+        }
     }
 }