CsvConvertUsingAnonymousTypeTest.cs

using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace UnitTestProject1
{
    [TestClass]
    public class CsvConvertUsingAnonymousTypeTest
    {
        public class Hoge
        {
            public int P1 { get; set; }
            public string P2 { get; set; }
        }

        [TestMethod]
        public void CsvConvertUsingAnonymousType()
        {
            var entities = new[] { 
                new Hoge(){ P1 = 10, P2 = "Hoge" }, 
                new Hoge(){ P1 = 20, P2 = "Fuga" },
                new Hoge(){ P1 = 30, P2 = "Piyo" }
            };

            var csvWithHeader = entities.ToCsv(n => new { n.P1, n.P2, P3 = n.P1 + n.P2 }, true);

            csvWithHeader.Is(
@"P1,P2,P3
10,Hoge,10Hoge
20,Fuga,20Fuga
30,Piyo,30Piyo");

            var csvNoHeader = entities.ToCsv(n => new { n.P1, n.P2, P3 = n.P1 + n.P2 }, false);

            csvNoHeader.Is(
@"10,Hoge,10Hoge
20,Fuga,20Fuga
30,Piyo,30Piyo");

            var Var1 = "local";

            var csvSample1 = entities.ToCsv(n => new { n.P1, n.P2, P3 = n.P1 + n.P2, Var1 }, true);

            csvSample1.Is(
@"P1,P2,P3,Var1
10,Hoge,10Hoge,local
20,Fuga,20Fuga,local
30,Piyo,30Piyo,local");

        }
    }

    public static class Csv
    {
        public static string ToCsv<T, TResult>(this IEnumerable<T> items, Expression<Func<T, TResult>> exp, bool withHeader = true)
        {
            if (!(exp.Body is NewExpression)) throw new ArgumentException("Requires NewExpression.", "exp");

            var ctor = (NewExpression)exp.Body;

            var header = from _ in " " where withHeader select ctor.Members.Select(n => n.Name).ToArray();

            var lambda = Expression.Lambda<Func<T, object[]>>(Expression.NewArrayInit(typeof(object), ctor.Arguments.Select(n => Expression.Convert(n, typeof(object)))), exp.Parameters[0]).Compile();

            return string.Join("\r\n", header.Concat(items.Select(lambda)).Select(n => string.Join(",", n.Select(s => EscForCsv(s)))));
        }

        private static object EscForCsv(object value)
        {
            //TODO Implement.
            return value;
        }
    }

}