Additional refactoring of Null Semantics

src/EFCore.Relational/Query/FromSqlParameterApplyingExpressionVisitor.cs

@@ -0,0 +1,134 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Data.Common;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq.Expressions;
+using Microsoft.EntityFrameworkCore.Internal;
+using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
+using Microsoft.EntityFrameworkCore.Storage;
+using Microsoft.EntityFrameworkCore.Storage.Internal;
+using Microsoft.EntityFrameworkCore.Utilities;
+
+namespace Microsoft.EntityFrameworkCore.Query
+{
+    public class FromSqlParameterApplyingExpressionVisitor : ExpressionVisitor
+    {
+        private readonly IDictionary<FromSqlExpression, Expression> _visitedFromSqlExpressions
+            = new Dictionary<FromSqlExpression, Expression>(ReferenceEqualityComparer.Instance);
+
+        private readonly ISqlExpressionFactory _sqlExpressionFactory;
+        private readonly ParameterNameGenerator _parameterNameGenerator;
+        private readonly IReadOnlyDictionary<string, object> _parametersValues;
+
+        public FromSqlParameterApplyingExpressionVisitor(
+            [NotNull] ISqlExpressionFactory sqlExpressionFactory,
+            [NotNull] ParameterNameGenerator parameterNameGenerator,
+            [NotNull] IReadOnlyDictionary<string, object> parametersValues)
+        {
+            Check.NotNull(sqlExpressionFactory, nameof(sqlExpressionFactory));
+            Check.NotNull(parameterNameGenerator, nameof(parameterNameGenerator));
+            Check.NotNull(parametersValues, nameof(parametersValues));
+
+            _sqlExpressionFactory = sqlExpressionFactory;
+            _parameterNameGenerator = parameterNameGenerator;
+            _parametersValues = parametersValues;
+        }
+
+        public override Expression Visit(Expression expression)
+        {
+            if (expression is FromSqlExpression fromSql)
+            {
+                if (!_visitedFromSqlExpressions.TryGetValue(fromSql, out var updatedFromSql))
+                {
+                    switch (fromSql.Arguments)
+                    {
+                        case ParameterExpression parameterExpression:
+                            var parameterValues = (object[])_parametersValues[parameterExpression.Name];
+
+                            var subParameters = new List<IRelationalParameter>(parameterValues.Length);
+                            // ReSharper disable once ForCanBeConvertedToForeach
+                            for (var i = 0; i < parameterValues.Length; i++)
+                            {
+                                var parameterName = _parameterNameGenerator.GenerateNext();
+                                if (parameterValues[i] is DbParameter dbParameter)
+                                {
+                                    if (string.IsNullOrEmpty(dbParameter.ParameterName))
+                                    {
+                                        dbParameter.ParameterName = parameterName;
+                                    }
+                                    else
+                                    {
+                                        parameterName = dbParameter.ParameterName;
+                                    }
+
+                                    subParameters.Add(new RawRelationalParameter(parameterName, dbParameter));
+                                }
+                                else
+                                {
+                                    subParameters.Add(
+                                        new TypeMappedRelationalParameter(
+                                            parameterName,
+                                            parameterName,
+                                            _sqlExpressionFactory.GetTypeMappingForValue(parameterValues[i]),
+                                            parameterValues[i]?.GetType().IsNullableType()));
+                                }
+                            }
+
+                            updatedFromSql = new FromSqlExpression(
+                                fromSql.Sql,
+                                Expression.Constant(
+                                    new CompositeRelationalParameter(
+                                        parameterExpression.Name,
+                                        subParameters)),
+                                fromSql.Alias);
+
+                            _visitedFromSqlExpressions[fromSql] = updatedFromSql;
+                            break;
+
+                        case ConstantExpression constantExpression:
+                            var existingValues = (object[])constantExpression.Value;
+                            var constantValues = new object[existingValues.Length];
+                            for (var i = 0; i < existingValues.Length; i++)
+                            {
+                                var value = existingValues[i];
+                                if (value is DbParameter dbParameter)
+                                {
+                                    var parameterName = _parameterNameGenerator.GenerateNext();
+                                    if (string.IsNullOrEmpty(dbParameter.ParameterName))
+                                    {
+                                        dbParameter.ParameterName = parameterName;
+                                    }
+                                    else
+                                    {
+                                        parameterName = dbParameter.ParameterName;
+                                    }
+
+                                    constantValues[i] = new RawRelationalParameter(parameterName, dbParameter);
+                                }
+                                else
+                                {
+                                    constantValues[i] = _sqlExpressionFactory.Constant(
+                                        value, _sqlExpressionFactory.GetTypeMappingForValue(value));
+                                }
+                            }
+
+                            updatedFromSql = new FromSqlExpression(
+                                fromSql.Sql,
+                                Expression.Constant(constantValues, typeof(object[])),
+                                fromSql.Alias);
+
+                            _visitedFromSqlExpressions[fromSql] = updatedFromSql;
+                            break;
+                    }
+                }
+
+                return updatedFromSql;
+            }
+
+            return base.Visit(expression);
+        }
+    }
+}