using System;

using System.Linq;

using System.Linq.Expressions;

public class Program

{

    public static void Main()

    {

        var someClass = new SomeClass

        {

            PropertyOne = "Value1",

            PropertyTwo = "Value2",

            PropertyThree = "Value3",

            PropertyFour = "Value4",

        };  

        var props = new string[] {"PropertyOne", "PropertyTwo" };

        Expression<Func<SomeClass, string>> keyFactoryExp = CreateExpression<SomeClass>(props);

        keyFactoryExp.Compile().Invoke(someClass).Dump();

    }

​

​

    static Expression<Func<T, string>> CreateExpression<T>(string[] props)

    {

        var par = Expression.Parameter(typeof(T));

        return Expression.Lambda<Func<T, string>>(Expression.Call(typeof(string).GetMethod("Join", new Type[] { typeof(string), typeof(object[]) }), Expression.Constant("|"),

            Expression.NewArrayInit(typeof(object), props.Select(prop => Expression.Property(par, prop)).ToArray())), par);

    }

​

    class SomeClass

    {

        public string PropertyOne { get; set; }

        public string PropertyTwo { get; set; }

        public string PropertyThree { get; set; }

        public string PropertyFour { get; set; }

    }

​

}