Fix to #32911 - ComplexProperty with AsSplitQuery

Problem was that when we lift structural type projection during pushdown, if that projection contains complex types with the same column names (e.g. cross join of same entities - it's perfectly fine to do in a vacuum, we just alias the columns whose names are repeated) we would lift the projection incorrectly.
What we do is go through all the properties, apply the corresponding columns to the selectExpression if needed and generate StructuralTypeProjection object if the projection needs to be applied one level up. For complex types we would generate a shaper expression and then run it through the same process, BUT the nested complex properties would be added to a flat structure along with the primitive properties, rather than in separate cache dedicated for complex property shapers.
This was wrong and not what we expected to see, when processing this structure one level up (i.e. when applying projection to the outer select)

SELECT [applying_this_projection_was_wrong]
FROM
(
    SELECT c.Id, c.Name, c.ComplexProp, o.ComplexProp as ComplexProp0
    FROM Customers as c
    JOIN Orders as o ON ...
) as s

i.e. applying projection once worked fine, but doing it second time did not. The reason why is that we expected to see information about the complex type shape in the complex property shaper cache, rather than flat structure for primitives, but it wasn't there. So we assumed this is the first time we the projection is being applied, so we conjure up the complex type shaper based on table alias and IColumn metadata. This results in a situation, where complex property that was aliased is never picked. So we end up with:

SELECT s.Id, s.Name, s.ComplexProp -- we would also try to add s.ComplexProp again, instead of s.ComplexProp0 but of course we don't add same thing twice
FROM
(
    SELECT c.Id, c.Name, c.ComplexProp, o.ComplexProp as ComplexProp0
    FROM Customers as c
    JOIN Orders as o ON ...
) as s

This leads to bad data - two different objects with distinct data in them are mapped to the same column in the database.

Fix is to property build a complex type shaper structure when applying projection instead, so the structure we generate matches expectations. Also modified VisitChildren and MakeNullable methods on StructuralTypeProjectionExpression to process/preserve complex type cache information, which was previously gobbled up/ignored.

Fixes #32911

Author: maumar

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

@@ -2077,20 +2077,21 @@ void HandleStructuralTypeProjection(
                         projection1.StructuralType.DisplayName(), projection2.StructuralType.DisplayName()));
             }
 
-            var propertyExpressions = new Dictionary<IProperty, ColumnExpression>();
-
-            ProcessStructuralType(projection1, projection2);
+            var resultProjection = ProcessStructuralType(projection1, projection2);
+            _projectionMapping[projectionMember] = resultProjection;
 
-            void ProcessStructuralType(
-                StructuralTypeProjectionExpression nestedProjection1,
-                StructuralTypeProjectionExpression nestedProjection2)
+            StructuralTypeProjectionExpression ProcessStructuralType(
+                StructuralTypeProjectionExpression structuralProjection1,
+                StructuralTypeProjectionExpression structuralProjection2)
             {
-                var type = nestedProjection1.StructuralType;
+                var propertyExpressions = new Dictionary<IProperty, ColumnExpression>();
+                var complexPropertyCache = new Dictionary<IComplexProperty, StructuralTypeShaperExpression>();
+                var type = structuralProjection1.StructuralType;
 
                 foreach (var property in type.GetAllPropertiesInHierarchy())
                 {
-                    var column1 = nestedProjection1.BindProperty(property);
-                    var column2 = nestedProjection2.BindProperty(property);
+                    var column1 = structuralProjection1.BindProperty(property);
+                    var column2 = structuralProjection2.BindProperty(property);
                     var alias = GenerateUniqueColumnAlias(column1.Name);
                     var innerProjection = new ProjectionExpression(column1, alias);
                     select1._projection.Add(innerProjection);
@@ -2127,7 +2128,7 @@ void ProcessStructuralType(
                         // If the top-level projection - not the current nested one - is a complex type and not an entity type, then add
                         // all its columns to the "otherExpressions" list (i.e. columns not part of a an entity primary key). This is
                         // the same as with a non-structural type projection.
-                        else if (projection1.StructuralType is IComplexType)
+                        else if (type is IComplexType)
                         {
                             var outerTypeMapping = column1.TypeMapping ?? column1.TypeMapping;
                             if (outerTypeMapping == null)
@@ -2141,52 +2142,62 @@ void ProcessStructuralType(
                     }
                 }
 
-                foreach (var complexProperty in GetAllComplexPropertiesInHierarchy(nestedProjection1.StructuralType))
+                foreach (var complexProperty in GetAllComplexPropertiesInHierarchy(type))
                 {
-                    ProcessStructuralType(
-                        (StructuralTypeProjectionExpression)nestedProjection1.BindComplexProperty(complexProperty).ValueBufferExpression,
-                        (StructuralTypeProjectionExpression)nestedProjection2.BindComplexProperty(complexProperty).ValueBufferExpression);
-                }
-            }
+                    var complexPropertyShaper1 = structuralProjection1.BindComplexProperty(complexProperty);
+                    var complexPropertyShaper2 = structuralProjection2.BindComplexProperty(complexProperty);
 
-            Check.DebugAssert(
-                projection1.TableMap.Count == projection2.TableMap.Count,
-                "Set operation over entity projections with different table map counts");
-            Check.DebugAssert(
-                projection1.TableMap.Keys.All(t => projection2.TableMap.ContainsKey(t)),
-                "Set operation over entity projections with table map discrepancy");
+                    var resultComplexProjection = ProcessStructuralType(
+                        (StructuralTypeProjectionExpression)complexPropertyShaper1.ValueBufferExpression,
+                        (StructuralTypeProjectionExpression)complexPropertyShaper2.ValueBufferExpression);
 
-            var tableMap = projection1.TableMap.ToDictionary(kvp => kvp.Key, _ => setOperationAlias);
+                    var resultComplexShaper = new RelationalStructuralTypeShaperExpression(
+                        complexProperty.ComplexType,
+                        resultComplexProjection,
+                        resultComplexProjection.IsNullable);
 
-            var discriminatorExpression = projection1.DiscriminatorExpression;
-            if (projection1.DiscriminatorExpression != null
-                && projection2.DiscriminatorExpression != null)
-            {
-                var alias = GenerateUniqueColumnAlias(DiscriminatorColumnAlias);
-                var innerProjection = new ProjectionExpression(projection1.DiscriminatorExpression, alias);
-                select1._projection.Add(innerProjection);
-                select2._projection.Add(new ProjectionExpression(projection2.DiscriminatorExpression, alias));
-                discriminatorExpression = CreateColumnExpression(innerProjection, setOperationAlias);
-            }
+                    complexPropertyCache[complexProperty] = resultComplexShaper;
+                }
 
-            var outerProjection = new StructuralTypeProjectionExpression(
-                projection1.StructuralType, propertyExpressions, tableMap, nullable: false, discriminatorExpression);
+                Check.DebugAssert(
+                    structuralProjection1.TableMap.Count == structuralProjection2.TableMap.Count,
+                    "Set operation over entity projections with different table map counts");
+                Check.DebugAssert(
+                    structuralProjection1.TableMap.Keys.All(t => structuralProjection2.TableMap.ContainsKey(t)),
+                    "Set operation over entity projections with table map discrepancy");
 
-            if (outerIdentifiers.Length > 0 && outerProjection is { StructuralType: IEntityType entityType })
-            {
-                var primaryKey = entityType.FindPrimaryKey();
+                var tableMap = projection1.TableMap.ToDictionary(kvp => kvp.Key, _ => setOperationAlias);
 
-                // We know that there are existing identifiers (see condition above); we know we must have a key since a keyless
-                // entity type would have wiped the identifiers when generating the join.
-                Check.DebugAssert(primaryKey != null, "primary key is null.");
-                foreach (var property in primaryKey.Properties)
+                var discriminatorExpression = structuralProjection1.DiscriminatorExpression;
+                if (structuralProjection1.DiscriminatorExpression != null
+                    && structuralProjection2.DiscriminatorExpression != null)
                 {
-                    entityProjectionIdentifiers.Add(outerProjection.BindProperty(property));
-                    entityProjectionValueComparers.Add(property.GetKeyValueComparer());
+                    var alias = GenerateUniqueColumnAlias(DiscriminatorColumnAlias);
+                    var innerProjection = new ProjectionExpression(structuralProjection1.DiscriminatorExpression, alias);
+                    select1._projection.Add(innerProjection);
+                    select2._projection.Add(new ProjectionExpression(structuralProjection2.DiscriminatorExpression, alias));
+                    discriminatorExpression = CreateColumnExpression(innerProjection, setOperationAlias);
                 }
-            }
 
-            _projectionMapping[projectionMember] = outerProjection;
+                var outerProjection = new StructuralTypeProjectionExpression(
+                    type, propertyExpressions, complexPropertyCache, tableMap, nullable: false, discriminatorExpression);
+
+                if (outerIdentifiers.Length > 0 && outerProjection is { StructuralType: IEntityType entityType })
+                {
+                    var primaryKey = entityType.FindPrimaryKey();
+
+                    // We know that there are existing identifiers (see condition above); we know we must have a key since a keyless
+                    // entity type would have wiped the identifiers when generating the join.
+                    Check.DebugAssert(primaryKey != null, "primary key is null.");
+                    foreach (var property in primaryKey.Properties)
+                    {
+                        entityProjectionIdentifiers.Add(outerProjection.BindProperty(property));
+                        entityProjectionValueComparers.Add(property.GetKeyValueComparer());
+                    }
+                }
+
+                return outerProjection;
+            }
         }
 
         string GenerateUniqueColumnAlias(string baseAlias)
@@ -2560,10 +2571,10 @@ public static StructuralTypeShaperExpression GenerateComplexPropertyShaperExpres
         // We do not support complex type splitting, so we will only ever have a single table/view mapping to it.
         // See Issue #32853 and Issue #31248
         var complexTypeTable = complexProperty.ComplexType.GetViewOrTableMappings().Single().Table;
-        if (!containerProjection.TableMap.TryGetValue(complexTypeTable, out var tableReferenceExpression))
+        if (!containerProjection.TableMap.TryGetValue(complexTypeTable, out var tableAlias))
         {
             complexTypeTable = complexProperty.ComplexType.GetDefaultMappings().Single().Table;
-            tableReferenceExpression = containerProjection.TableMap[complexTypeTable];
+            tableAlias = containerProjection.TableMap[complexTypeTable];
         }
         var isComplexTypeNullable = containerProjection.IsNullable || complexProperty.IsNullable;
 
@@ -2581,14 +2592,14 @@ public static StructuralTypeShaperExpression GenerateComplexPropertyShaperExpres
             // TODO: Reimplement EntityProjectionExpression via TableMap, and then use that here
             var column = complexTypeTable.FindColumn(property)!;
             propertyExpressionMap[property] = CreateColumnExpression(
-                property, column, tableReferenceExpression, isComplexTypeNullable || column.IsNullable);
+                property, column, tableAlias, isComplexTypeNullable || column.IsNullable);
         }
 
         // The table map of the target complex type should only ever contains a single table (no table splitting).
         // If the source is itself a complex type (nested complex type), its table map is already suitable and we can just pass it on.
         var newTableMap = containerProjection.TableMap.Count == 1
             ? containerProjection.TableMap
-            : new Dictionary<ITableBase, string> { [complexTypeTable] = tableReferenceExpression };
+            : new Dictionary<ITableBase, string> { [complexTypeTable] = tableAlias };
 
         Check.DebugAssert(newTableMap.Single().Key == complexTypeTable, "Bad new table map");
 
@@ -3530,33 +3541,35 @@ StructuralTypeProjectionExpression LiftEntityProjectionFromSubquery(
             string subqueryAlias)
         {
             var propertyExpressions = new Dictionary<IProperty, ColumnExpression>();
+            var complexPropertyCache = new Dictionary<IComplexProperty, StructuralTypeShaperExpression>();
 
-            HandleTypeProjection(projection);
-
-            void HandleTypeProjection(StructuralTypeProjectionExpression typeProjection)
+            foreach (var property in projection.StructuralType.GetAllPropertiesInHierarchy())
             {
-                foreach (var property in typeProjection.StructuralType.GetAllPropertiesInHierarchy())
+                // json entity projection (i.e. JSON entity that was transformed into query root) may have synthesized keys
+                // but they don't correspond to any columns - we need to skip those
+                if (projection is { StructuralType: IEntityType entityType }
+                    && entityType.IsMappedToJson()
+                    && property.IsOrdinalKeyProperty())
                 {
-                    // json entity projection (i.e. JSON entity that was transformed into query root) may have synthesized keys
-                    // but they don't correspond to any columns - we need to skip those
-                    if (typeProjection is { StructuralType: IEntityType entityType }
-                        && entityType.IsMappedToJson()
-                        && property.IsOrdinalKeyProperty())
-                    {
-                        continue;
-                    }
-
-                    var innerColumn = typeProjection.BindProperty(property);
-                    var outerColumn = subquery.GenerateOuterColumn(subqueryAlias, innerColumn);
-                    projectionMap[innerColumn] = outerColumn;
-                    propertyExpressions[property] = outerColumn;
+                    continue;
                 }
 
-                foreach (var complexProperty in GetAllComplexPropertiesInHierarchy(typeProjection.StructuralType))
-                {
-                    HandleTypeProjection(
-                        (StructuralTypeProjectionExpression)typeProjection.BindComplexProperty(complexProperty).ValueBufferExpression);
-                }
+                var innerColumn = projection.BindProperty(property);
+                var outerColumn = subquery.GenerateOuterColumn(subqueryAlias, innerColumn);
+
+                projectionMap[innerColumn] = outerColumn;
+                propertyExpressions[property] = outerColumn;
+            }
+
+            foreach (var complexProperty in GetAllComplexPropertiesInHierarchy(projection.StructuralType))
+            {
+                var complexPropertyShaper = projection.BindComplexProperty(complexProperty);
+
+                var complexTypeProjectionExpression = LiftEntityProjectionFromSubquery(
+                    (StructuralTypeProjectionExpression)complexPropertyShaper.ValueBufferExpression,
+                    subqueryAlias);
+
+                complexPropertyCache[complexProperty] = complexPropertyShaper.Update(complexTypeProjectionExpression);
             }
 
             ColumnExpression? discriminatorExpression = null;
@@ -3570,7 +3583,7 @@ void HandleTypeProjection(StructuralTypeProjectionExpression typeProjection)
             var tableMap = projection.TableMap.ToDictionary(kvp => kvp.Key, _ => subqueryAlias);
 
             var newEntityProjection = new StructuralTypeProjectionExpression(
-                projection.StructuralType, propertyExpressions, tableMap, nullable: false, discriminatorExpression);
+                projection.StructuralType, propertyExpressions, complexPropertyCache, tableMap, nullable: false, discriminatorExpression);
 
             if (projection.StructuralType is IEntityType entityType2)
             {