Skips normalization of array[index].Property to array.Select(e => e.P…

…roperty).ElementAt(index), because it messes-up our JSON-Array handling in `MySqlSqlTranslatingExpressionVisitor`. See dotnet/efcore#30386.

src/EFCore.MySql/Extensions/MySqlServiceCollectionExtensions.cs

@@ -130,6 +130,7 @@ public static IServiceCollection AddEntityFrameworkMySql([NotNull] this IService
                 //.TryAdd<IValueConverterSelector, MySqlValueConverterSelector>()
                 .TryAdd<IQueryCompilationContextFactory, MySqlQueryCompilationContextFactory>()
                 .TryAdd<IQueryTranslationPostprocessorFactory, MySqlQueryTranslationPostprocessorFactory>()
+                .TryAdd<IQueryTranslationPreprocessorFactory, MySqlQueryTranslationPreprocessorFactory>()
                 .TryAdd<IMigrationsModelDiffer, MySqlMigrationsModelDiffer>()
                 .TryAdd<IMigrator, MySqlMigrator>()
                 .TryAddProviderSpecificServices(m => m

src/EFCore.MySql/Query/ExpressionVisitors/Internal/MySqlQueryTranslationPreprocessor.cs

@@ -0,0 +1,38 @@
+// Copyright (c) Pomelo Foundation. All rights reserved.
+// Licensed under the MIT. See LICENSE in the project root for license information.
+
+using System.Linq.Expressions;
+using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
+
+namespace Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal;
+
+public class MySqlQueryTranslationPreprocessor : RelationalQueryTranslationPreprocessor
+{
+    private readonly RelationalQueryCompilationContext _relationalQueryCompilationContext;
+
+    public MySqlQueryTranslationPreprocessor(
+        QueryTranslationPreprocessorDependencies dependencies,
+        RelationalQueryTranslationPreprocessorDependencies relationalDependencies,
+        QueryCompilationContext queryCompilationContext)
+        : base(dependencies, relationalDependencies, queryCompilationContext)
+    {
+        _relationalQueryCompilationContext = (RelationalQueryCompilationContext)queryCompilationContext;
+    }
+
+    /// <summary>
+    /// Workaround https://github.com/dotnet/efcore/issues/30386.
+    /// </summary>
+    public override Expression NormalizeQueryableMethod(Expression expression)
+    {
+        // Implementation of base (RelationalQueryTranslationPreprocessor).
+        expression = new RelationalQueryMetadataExtractingExpressionVisitor(_relationalQueryCompilationContext).Visit(expression);
+
+        // Implementation of base.base (QueryTranslationPreprocessor), using `MySqlQueryableMethodNormalizingExpressionVisitor` instead of
+        // `QueryableMethodNormalizingExpressionVisitor` directly.
+        expression = new MySqlQueryableMethodNormalizingExpressionVisitor(QueryCompilationContext).Normalize(expression);
+        expression = ProcessQueryRoots(expression);
+
+        return expression;
+    }
+}

src/EFCore.MySql/Query/ExpressionVisitors/Internal/MySqlQueryTranslationPreprocessorFactory.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Pomelo Foundation. All rights reserved.
+// Licensed under the MIT. See LICENSE in the project root for license information.
+
+using Microsoft.EntityFrameworkCore.Query;
+
+namespace Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal;
+
+public class MySqlQueryTranslationPreprocessorFactory : IQueryTranslationPreprocessorFactory
+{
+    private readonly QueryTranslationPreprocessorDependencies _dependencies;
+    private readonly RelationalQueryTranslationPreprocessorDependencies _relationalDependencies;
+
+    public MySqlQueryTranslationPreprocessorFactory(
+        QueryTranslationPreprocessorDependencies dependencies,
+        RelationalQueryTranslationPreprocessorDependencies relationalDependencies)
+    {
+        _dependencies = dependencies;
+        _relationalDependencies = relationalDependencies;
+    }
+
+    public virtual QueryTranslationPreprocessor Create(QueryCompilationContext queryCompilationContext)
+        => new MySqlQueryTranslationPreprocessor(
+            _dependencies,
+            _relationalDependencies,
+            queryCompilationContext);
+}

src/EFCore.MySql/Query/ExpressionVisitors/Internal/MySqlQueryableMethodNormalizingExpressionVisitor.cs

@@ -0,0 +1,74 @@
+// Copyright (c) Pomelo Foundation. All rights reserved.
+// Licensed under the MIT. See LICENSE in the project root for license information.
+
+using System;
+using System.Linq.Expressions;
+using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
+
+namespace Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal;
+
+/// <summary>
+/// Skips normalization of array[index].Property to array.Select(e => e.Property).ElementAt(index),
+/// because it messes-up our JSON-Array handling in `MySqlSqlTranslatingExpressionVisitor`.
+/// See https://github.com/dotnet/efcore/issues/30386.
+/// </summary>
+public class MySqlQueryableMethodNormalizingExpressionVisitor : QueryableMethodNormalizingExpressionVisitor
+{
+    public MySqlQueryableMethodNormalizingExpressionVisitor(QueryCompilationContext queryCompilationContext)
+        : base(queryCompilationContext)
+    {
+    }
+
+    protected override Expression VisitBinary(BinaryExpression binaryExpression)
+    {
+        // Convert array[x] to array.ElementAt(x)
+        if (binaryExpression is
+            {
+                NodeType: ExpressionType.ArrayIndex,
+                Left: var source,
+                Right: var index
+            })
+        {
+            return binaryExpression;
+
+            // Original (base) implementation:
+            //
+            // return VisitMethodCall(
+            //     Expression.Call(
+            //         ElementAtMethodInfo.MakeGenericMethod(source.Type.GetSequenceType()), source, index));
+        }
+
+        return base.VisitBinary(binaryExpression);
+    }
+
+    protected override Expression VisitMethodCall(MethodCallExpression methodCallExpression)
+    {
+        // Normalize list[x] to list.ElementAt(x)
+        if (methodCallExpression is
+            {
+                Method:
+                {
+                    Name: "get_Item",
+                    IsStatic: false,
+                    DeclaringType: Type declaringType
+                },
+                Object: Expression indexerSource,
+                Arguments: [var index]
+            }
+            && declaringType.GetInterface("IReadOnlyList`1") is not null)
+        {
+            return methodCallExpression;
+
+            // Original (base) implementation:
+            //
+            // return VisitMethodCall(
+            //     Expression.Call(
+            //         ElementAtMethodInfo.MakeGenericMethod(indexerSource.Type.GetSequenceType()),
+            //         indexerSource,
+            //         index));
+        }
+
+        return base.VisitMethodCall(methodCallExpression);
+    }
+}