using System;

using System.Collections.ObjectModel;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

​

namespace ExpressionVisitorTests

{

​

    public class Program

    {

        public static void Main()

        {

            var colourRepository = new ColourRepository();

            var result = colourRepository.GetWhere(c => c.Name == "Red");

            Console.WriteLine(result.Count());

        }

    }

    public class DtoColour {

        public DtoColour(string name)

        {

            Name = name;

        }

        public string Name { get; set; }

    }

    public class DomainColour {

        public DomainColour(string name)

        {

            Name = name;

        }

        public string Name { get; set; }

    }

    public class ColourRepository {

        private IList<DtoColour> Colours { get; set; } 

        public ColourRepository()

        {

            Colours = new List<DtoColour>()

                {

                    new DtoColour("Red"),

                    new DtoColour("Blue"),

                    new DtoColour("Yellow")

                };

        }

        public IEnumerable<DomainColour> GetWhere(Expression<Func<DomainColour, bool>> predicate)

        {

            var coonvertedPred = MyExpressionVisitor.Convert(predicate);

            return Colours.Where(coonvertedPred).Select(c => new DomainColour(c.Name)).ToList();

        }

    }

    public class MyExpressionVisitor : ExpressionVisitor

    {

        private ReadOnlyCollection<ParameterExpression> _parameters;

        public static Func<DtoColour, bool> Convert<T>(Expression<T> root)

        {

            var visitor = new MyExpressionVisitor();

            var expression = (Expression<Func<DtoColour, bool>>)visitor.Visit(root);

            return expression.Compile();

        }

​

        protected override Expression VisitParameter(ParameterExpression node)

        {

            return (_parameters != null)? _parameters.FirstOrDefault(p => p.Name == node.Name) :

                   (node.Type == typeof(DomainColour) ? Expression.Parameter(typeof(DtoColour), node.Name) : node);

        }

        protected override Expression VisitLambda<T>(Expression<T> node)

        {

            _parameters = VisitAndConvert<ParameterExpression>(node.Parameters, "VisitLambda");

            return Expression.Lambda(Visit(node.Body), _parameters);

        }

​

        protected override Expression VisitMember(MemberExpression node)

        {

            if (node.Member.DeclaringType == typeof(DomainColour))

            {

                return Expression.MakeMemberAccess(Visit(node.Expression), typeof(DtoColour).GetProperty(node.Member.Name));

            }

            return base.VisitMember(node);

        }

    }

}