Cosmos: Fixes around array projection

Closes #33797

src/EFCore.Cosmos/Extensions/Internal/CosmosShapedQueryExpressionExtensions.cs

@@ -63,8 +63,7 @@ public static bool TryConvertToArray(
         {
             subquery.ApplyProjection();
 
-            // TODO: Should the type be an array, or enumerable/queryable?
-            var arrayClrType = projection.Type.MakeArrayType();
+            var arrayClrType = typeof(IEnumerable<>).MakeGenericType(projection.Type);
 
             switch (projection)
             {

src/EFCore.Cosmos/Query/Internal/CosmosProjectionBindingExpressionVisitor.cs

@@ -5,6 +5,8 @@
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Cosmos.Internal;
 using Microsoft.EntityFrameworkCore.Cosmos.Metadata.Internal;
+using Microsoft.EntityFrameworkCore.Cosmos.Storage.Internal;
+using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Query.Internal;
 
 namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal;
@@ -21,7 +23,9 @@ private static readonly MethodInfo GetParameterValueMethodInfo
         = typeof(CosmosProjectionBindingExpressionVisitor)
             .GetTypeInfo().GetDeclaredMethod(nameof(GetParameterValue))!;
 
+    private readonly CosmosQueryableMethodTranslatingExpressionVisitor _queryableMethodTranslatingExpressionVisitor;
     private readonly CosmosSqlTranslatingExpressionVisitor _sqlTranslator;
+    private readonly ITypeMappingSource _typeMappingSource;
     private readonly IModel _model;
     private SelectExpression _selectExpression;
     private bool _clientEval;
@@ -39,10 +43,14 @@ private static readonly MethodInfo GetParameterValueMethodInfo
     /// </summary>
     public CosmosProjectionBindingExpressionVisitor(
         IModel model,
-        CosmosSqlTranslatingExpressionVisitor sqlTranslator)
+        CosmosQueryableMethodTranslatingExpressionVisitor queryableMethodTranslatingExpressionVisitor,
+        CosmosSqlTranslatingExpressionVisitor sqlTranslator,
+        ITypeMappingSource typeMappingSource)
     {
         _model = model;
+        _queryableMethodTranslatingExpressionVisitor = queryableMethodTranslatingExpressionVisitor;
         _sqlTranslator = sqlTranslator;
+        _typeMappingSource = typeMappingSource;
         _selectExpression = null!;
     }
 
@@ -570,6 +578,50 @@ UnaryExpression unaryExpression
                             lambda);
                 }
             }
+            else if (method is { Name: nameof(Enumerable.ToList), IsGenericMethod: true }
+                     && method.DeclaringType == typeof(Enumerable)
+                     && methodCallExpression.Arguments is [var argument]
+                     && argument.Type.TryGetElementType(typeof(IQueryable<>)) != null)
+            {
+                if (_queryableMethodTranslatingExpressionVisitor.TranslateSubquery(argument) is not ShapedQueryExpression subquery
+                    || !subquery.TryConvertToArray(_typeMappingSource, out var array))
+                {
+                    throw new InvalidOperationException(CoreStrings.TranslationFailed(methodCallExpression.Print()));
+                }
+
+                // If ToList() was composed over a subquery with operators, the result here is an ArrayExpression (ARRAY(SELECT ...)), whose
+                // CLR Type is IEnumerable<T>. This can be directly used in the resulting ProjectingBindingExpression - the shaper will
+                // simply read the JSON results out successfully.
+                // But if ToList() is composed directly over an array property, that property could have type e.g. T[], which will be read
+                // in the shaper, and then the cast from T[] to List<T> will fail. As a result, wrap the array in an additional
+                // "reprojection" subquery, effectively to change the CLR type.
+                if (array is SqlExpression scalarArray
+                    && !(array.Type.IsGenericType && array.Type.GetGenericTypeDefinition() == typeof(IEnumerable<>)))
+                {
+                    Check.DebugAssert(
+                        array is not ScalarArrayExpression and not ObjectArrayExpression, "ArrayExpression should be IEnumerable");
+
+                    if (scalarArray is not { TypeMapping.ElementTypeMapping: CosmosTypeMapping elementTypeMapping })
+                    {
+                        throw new UnreachableException("Scalar array with no element type mapping");
+                    }
+
+                    // TODO: Proper alias management (#33894).
+                    var arrayReprojectionSubquery = SelectExpression.CreateForCollection(
+                        array, "i", new ScalarReferenceExpression("i", elementTypeMapping.ClrType, elementTypeMapping));
+                    arrayReprojectionSubquery.ApplyProjection();
+
+                    array = new ScalarArrayExpression(
+                        arrayReprojectionSubquery,
+                        methodCallExpression.Type, // List<>
+                        _typeMappingSource.FindMapping(methodCallExpression.Type, _model, elementTypeMapping));
+                }
+
+                return new ProjectionBindingExpression(
+                    _selectExpression,
+                    _selectExpression.AddToProjection(array),
+                    methodCallExpression.Type);
+            }
         }
 
         var @object = Visit(methodCallExpression.Object);

src/EFCore.Cosmos/Query/Internal/CosmosQueryableMethodTranslatingExpressionVisitor.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.EntityFrameworkCore.Cosmos.Internal;
 using Microsoft.EntityFrameworkCore.Cosmos.Metadata.Internal;
+using Microsoft.EntityFrameworkCore.Cosmos.Storage.Internal;
 using Microsoft.EntityFrameworkCore.Internal;
 
 namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal;
@@ -54,7 +55,7 @@ public CosmosQueryableMethodTranslatingExpressionVisitor(
             _methodCallTranslatorProvider,
             this);
         _projectionBindingExpressionVisitor =
-            new CosmosProjectionBindingExpressionVisitor(_queryCompilationContext.Model, _sqlTranslator);
+            new CosmosProjectionBindingExpressionVisitor(_queryCompilationContext.Model, this, _sqlTranslator, _typeMappingSource);
         _subquery = false;
     }
 
@@ -81,7 +82,7 @@ protected CosmosQueryableMethodTranslatingExpressionVisitor(
             _methodCallTranslatorProvider,
             parentVisitor);
         _projectionBindingExpressionVisitor =
-            new CosmosProjectionBindingExpressionVisitor(_queryCompilationContext.Model, _sqlTranslator);
+            new CosmosProjectionBindingExpressionVisitor(_queryCompilationContext.Model, this, _sqlTranslator, _typeMappingSource);
         _subquery = true;
     }
 
@@ -1125,8 +1126,10 @@ protected override ShapedQueryExpression TranslateSelect(ShapedQueryExpression s
             // ElementAtOrDefault over an array of scalars
             case SqlExpression scalarArray when projection is SqlExpression element:
             {
-                var slice = _sqlExpressionFactory.Function(
-                    "ARRAY_SLICE", [scalarArray, translatedCount], scalarArray.Type, scalarArray.TypeMapping);
+                var arrayType = typeof(IEnumerable<>).MakeGenericType(projection.Type);
+                var arrayTypeMapping = _typeMappingSource.FindMapping(arrayType, _queryCompilationContext.Model, element.TypeMapping);
+
+                var slice = _sqlExpressionFactory.Function("ARRAY_SLICE", [scalarArray, translatedCount], arrayType, arrayTypeMapping);
 
                 // TODO: Proper alias management (#33894). Ideally reach into the source of the original SelectExpression and use that alias.
                 var translatedSelect = SelectExpression.CreateForCollection(
@@ -1139,8 +1142,10 @@ protected override ShapedQueryExpression TranslateSelect(ShapedQueryExpression s
             // ElementAtOrDefault over an array os structural types
             case not null when projectedStructuralTypeShaper is not null:
             {
+                var arrayType = typeof(IEnumerable<>).MakeGenericType(projectedStructuralTypeShaper.Type);
+
                 // TODO: Proper alias management (#33894).
-                var slice = new ObjectFunctionExpression("ARRAY_SLICE", [array, translatedCount], projectedStructuralTypeShaper.Type);
+                var slice = new ObjectFunctionExpression("ARRAY_SLICE", [array, translatedCount], arrayType);
                 var translatedSelect = SelectExpression.CreateForCollection(
                     slice,
                     "i",
@@ -1585,7 +1590,7 @@ when methodCallExpression.TryGetIndexerArguments(_queryCompilationContext.Model,
         // value conversion). #34026.
         var elementClrType = inlineQueryRootExpression.ElementType;
         var elementTypeMapping = _typeMappingSource.FindMapping(elementClrType)!;
-        var arrayTypeMapping = _typeMappingSource.FindMapping(elementClrType.MakeArrayType()); // TODO: IEnumerable?
+        var arrayTypeMapping = _typeMappingSource.FindMapping(typeof(IEnumerable<>).MakeGenericType(elementClrType));
         var inlineArray = new ArrayConstantExpression(elementClrType, translatedItems, arrayTypeMapping);
 
         // TODO: Do proper alias management: #33894
@@ -1614,7 +1619,7 @@ when methodCallExpression.TryGetIndexerArguments(_queryCompilationContext.Model,
         // TODO: Temporary hack - need to perform proper derivation of the array type mapping from the element (e.g. for
         // value conversion). #34026.
         var elementClrType = parameterQueryRootExpression.ElementType;
-        var arrayTypeMapping = _typeMappingSource.FindMapping(elementClrType.MakeArrayType()); // TODO: IEnumerable?
+        var arrayTypeMapping = _typeMappingSource.FindMapping(typeof(IEnumerable<>).MakeGenericType(elementClrType));
         var elementTypeMapping = _typeMappingSource.FindMapping(elementClrType)!;
         var sqlParameterExpression = new SqlParameterExpression(parameterQueryRootExpression.ParameterExpression, arrayTypeMapping);
 
@@ -1683,13 +1688,17 @@ when methodCallExpression.TryGetIndexerArguments(_queryCompilationContext.Model,
             && source2.TryConvertToArray(_typeMappingSource, out var array2, out var projection2, ignoreOrderings)
             && projection1.Type == projection2.Type)
         {
+            var arrayType = typeof(IEnumerable<>).MakeGenericType(projection1.Type);
+
             // Set operation over arrays of scalars
             if (projection1 is SqlExpression sqlProjection1
                 && projection2 is SqlExpression sqlProjection2
-                && (sqlProjection1.TypeMapping ?? sqlProjection2.TypeMapping) is CoreTypeMapping typeMapping)
+                && (sqlProjection1.TypeMapping ?? sqlProjection2.TypeMapping) is CosmosTypeMapping typeMapping)
             {
+                var arrayTypeMapping = _typeMappingSource.FindMapping(arrayType, _queryCompilationContext.Model, typeMapping);
+
                 // TODO: Proper alias management (#33894).
-                var translation = _sqlExpressionFactory.Function(functionName, [array1, array2], projection1.Type, typeMapping);
+                var translation = _sqlExpressionFactory.Function(functionName, [array1, array2], arrayType, arrayTypeMapping);
                 var select = SelectExpression.CreateForCollection(
                     translation, "i", new ScalarReferenceExpression("i", projection1.Type, typeMapping));
                 return source1.UpdateQueryExpression(select);
@@ -1701,7 +1710,7 @@ when methodCallExpression.TryGetIndexerArguments(_queryCompilationContext.Model,
                 && structuralType1 == structuralType2)
             {
                 // TODO: Proper alias management (#33894).
-                var translation = new ObjectFunctionExpression(functionName, [array1, array2], projection1.Type);
+                var translation = new ObjectFunctionExpression(functionName, [array1, array2], arrayType);
                 var select = SelectExpression.CreateForCollection(
                     translation, "i", new ObjectReferenceExpression((IEntityType)structuralType1, "i"));
                 return CreateShapedQueryExpression(select, structuralType1.ClrType);

src/EFCore.Cosmos/Query/Internal/Expressions/ScalarAccessExpression.cs

@@ -13,6 +13,7 @@ namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal;
 ///     any release. You should only use it directly in your code with extreme caution and knowing that
 ///     doing so can result in application failures when updating to a new Entity Framework Core release.
 /// </remarks>
+[DebuggerDisplay("{Microsoft.EntityFrameworkCore.Query.ExpressionPrinter.Print(this), nq}")]
 public class ScalarAccessExpression(Expression @object, string propertyName, Type clrType, CoreTypeMapping? typeMapping)
     : SqlExpression(clrType, typeMapping), IAccessExpression
 {

src/EFCore.Cosmos/Query/Internal/Expressions/SelectExpression.cs

@@ -322,27 +322,9 @@ public virtual void ReplaceProjectionMapping(IDictionary<ProjectionMember, Expre
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    public virtual int AddToProjection(SqlExpression sqlExpression)
+    public virtual int AddToProjection(Expression sqlExpression)
         => AddToProjection(sqlExpression, null);
 
-    /// <summary>
-    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
-    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
-    ///     any release. You should only use it directly in your code with extreme caution and knowing that
-    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
-    /// </summary>
-    public virtual int AddToProjection(EntityProjectionExpression entityProjection)
-        => AddToProjection(entityProjection, null);
-
-    /// <summary>
-    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
-    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
-    ///     any release. You should only use it directly in your code with extreme caution and knowing that
-    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
-    /// </summary>
-    public virtual int AddToProjection(ObjectArrayAccessExpression objectArrayAccess)
-        => AddToProjection(objectArrayAccess, null);
-
     private int AddToProjection(Expression expression, string? alias)
     {
         var existingIndex = _projection.FindIndex(pe => pe.Expression.Equals(expression));

src/EFCore.Cosmos/Query/Internal/SqlExpressionFactory.cs

@@ -165,7 +165,7 @@ private SqlExpression ApplyTypeMappingOnSqlBinary(
                 // TODO: This infers based on the CLR type; need to properly infer based on the element type mapping
                 // TODO: being applied here (e.g. WHERE @p[1] = c.PropertyWithValueConverter). #34026
                 var arrayTypeMapping = left.TypeMapping
-                    ?? (typeMapping is null ? null : typeMappingSource.FindMapping(typeMapping.ClrType.MakeArrayType()));
+                    ?? (typeMapping is null ? null : typeMappingSource.FindMapping(typeof(IEnumerable<>).MakeGenericType(typeMapping.ClrType)));
                 return new SqlBinaryExpression(
                     ExpressionType.ArrayIndex,
                     ApplyTypeMapping(left, arrayTypeMapping),
@@ -290,7 +290,7 @@ private InExpression ApplyTypeMappingOnIn(InExpression inExpression)
             var arrayClrType = arrayExpression.Type switch
             {
                 var t when t.TryGetSequenceType() != typeof(object) => t,
-                { IsArray: true } => itemExpression.Type.MakeArrayType(),
+                { IsArray: true } => typeof(IEnumerable<>).MakeGenericType(itemExpression.Type),
                 { IsConstructedGenericType: true, GenericTypeArguments.Length: 1 } t
                     => t.GetGenericTypeDefinition().MakeGenericType(itemExpression.Type),
                 _ => throw new InvalidOperationException(

test/EFCore.Cosmos.FunctionalTests/Query/OwnedQueryCosmosTest.cs

@@ -309,8 +309,8 @@ public override Task Where_owned_collection_navigation_ToList_Count(bool async)
             async, async a =>
             {
                 // TODO: #34011
-                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets persisted
-                // as null instead of [].
+                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets
+                // persisted as null instead of [] when there are no Details. So we change the Count we check to 1.
                 await AssertQuery(
                     a,
                     ss => ss.Set<OwnedPerson>()
@@ -323,7 +323,7 @@ await AssertQuery(
 
                 AssertSql(
                     """
-SELECT a
+SELECT a["Details"]
 FROM root c
 JOIN a IN c["Orders"]
 WHERE (c["Discriminator"] IN ("OwnedPerson", "Branch", "LeafB", "LeafA") AND (ARRAY_LENGTH(a["Details"]) = 1))
@@ -336,8 +336,8 @@ public override Task Where_collection_navigation_ToArray_Count(bool async)
             async, async a =>
             {
                 // TODO: #34011
-                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets persisted
-                // as null instead of [].
+                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets
+                // persisted as null instead of [] when there are no Details. So we change the Count we check to 1.
                 await AssertQuery(
                     a,
                     ss => ss.Set<OwnedPerson>()
@@ -363,8 +363,8 @@ public override Task Where_collection_navigation_AsEnumerable_Count(bool async)
             async, async a =>
             {
                 // TODO: #34011
-                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets persisted
-                // as null instead of [].
+                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets
+                // persisted as null instead of [] when there are no Details. So we change the Count we check to 1.
                 await AssertQuery(
                     a,
                     ss => ss.Set<OwnedPerson>()
@@ -390,8 +390,8 @@ public override Task Where_collection_navigation_ToList_Count_member(bool async)
             async, async a =>
             {
                 // TODO: #34011
-                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets persisted
-                // as null instead of [].
+                // We override this test because the test data for this class gets saved incorrectly - the Order.Details collection gets
+                // persisted as null instead of [] when there are no Details. So we change the Count we check to 1.
                 await AssertQuery(
                     a,
                     ss => ss.Set<OwnedPerson>()
@@ -404,7 +404,7 @@ await AssertQuery(
 
                 AssertSql(
                     """
-SELECT a
+SELECT a["Details"]
 FROM root c
 JOIN a IN c["Orders"]
 WHERE (c["Discriminator"] IN ("OwnedPerson", "Branch", "LeafB", "LeafA") AND (ARRAY_LENGTH(a["Details"]) = 1))