ExpressionHelper.cs

// 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.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Web.Mvc.ExpressionUtil;
using System.Web.Mvc.Properties;

namespace System.Web.Mvc
{
    public static class ExpressionHelper
    {
        public static string GetExpressionText(string expression)
        {
            return
                String.Equals(expression, "model", StringComparison.OrdinalIgnoreCase)
                    ? String.Empty // If it's exactly "model", then give them an empty string, to replicate the lambda behavior
                    : expression;
        }

        public static string GetExpressionText(LambdaExpression expression)
        {
            // Split apart the expression string for property/field accessors to create its name
            Stack<string> nameParts = new Stack<string>();
            Expression part = expression.Body;

            while (part != null)
            {
                if (part.NodeType == ExpressionType.Call)
                {
                    MethodCallExpression methodExpression = (MethodCallExpression)part;

                    if (!IsSingleArgumentIndexer(methodExpression))
                    {
                        // Unsupported
                        break;
                    }

                    nameParts.Push(
                        GetIndexerInvocation(
                            methodExpression.Arguments.Single(),
                            expression.Parameters.ToArray()));

                    part = methodExpression.Object;
                }
                else if (part.NodeType == ExpressionType.ArrayIndex)
                {
                    BinaryExpression binaryExpression = (BinaryExpression)part;

                    nameParts.Push(
                        GetIndexerInvocation(
                            binaryExpression.Right,
                            expression.Parameters.ToArray()));

                    part = binaryExpression.Left;
                }
                else if (part.NodeType == ExpressionType.MemberAccess)
                {
                    MemberExpression memberExpressionPart = (MemberExpression)part;
                    var name = memberExpressionPart.Member.Name;

                    // If identifier contains "__", it is "reserved for use by the implementation" and likely compiler-
                    // or Razor-generated e.g. the name of a field in a delegate's generated class.
                    if (name.Contains("__"))
                    {
                        // Exit loop. Should have the entire name because previous MemberAccess has same name as the
                        // leftmost expression node (a variable).
                        break;
                    }

                    nameParts.Push("." + name);
                    part = memberExpressionPart.Expression;
                }
                else if (part.NodeType == ExpressionType.Parameter)
                {
                    // Dev10 Bug #907611
                    // When the expression is parameter based (m => m.Something...), we'll push an empty
                    // string onto the stack and stop evaluating. The extra empty string makes sure that
                    // we don't accidentally cut off too much of m => m.Model.
                    nameParts.Push(String.Empty);

                    // Exit loop. Have the entire name because the parameter cannot be used as an indexer; always the
                    // leftmost expression node.
                    break;
                }
                else
                {
                    // Unsupported
                    break;
                }
            }

            // If parts start with "model", then strip that part away.
            if (nameParts.Count > 0 && String.Equals(nameParts.Peek(), ".model", StringComparison.OrdinalIgnoreCase))
            {
                nameParts.Pop();
            }

            if (nameParts.Count > 0)
            {
                return nameParts.Aggregate((left, right) => left + right).TrimStart('.');
            }

            return String.Empty;
        }

        private static string GetIndexerInvocation(Expression expression, ParameterExpression[] parameters)
        {
            Expression converted = Expression.Convert(expression, typeof(object));
            ParameterExpression fakeParameter = Expression.Parameter(typeof(object), null);
            Expression<Func<object, object>> lambda = Expression.Lambda<Func<object, object>>(converted, fakeParameter);
            Func<object, object> func;

            try
            {
                func = CachedExpressionCompiler.Process(lambda);
            }
            catch (InvalidOperationException ex)
            {
                throw new InvalidOperationException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.ExpressionHelper_InvalidIndexerExpression,
                        expression,
                        parameters[0].Name),
                    ex);
            }

            return "[" + Convert.ToString(func(null), CultureInfo.InvariantCulture) + "]";
        }

        internal static bool IsSingleArgumentIndexer(Expression expression)
        {
            MethodCallExpression methodExpression = expression as MethodCallExpression;
            if (methodExpression == null || methodExpression.Arguments.Count != 1)
            {
                return false;
            }

            return methodExpression.Method
                .DeclaringType
                .GetDefaultMembers()
                .OfType<PropertyInfo>()
                .Any(p => p.GetGetMethod() == methodExpression.Method);
        }
    }
}