using System;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

public class Program

{

    public static void Main()

    {

        var p = new Parent() { Children = new List<ChildA>() };

        var child1 = new ChildA() { Name = "Joe" };

        var child2 = new ChildA() { Name = "Sarah" };

        var child3 = new ChildA() { Name = "Mike" };

//      var child4 = new ChildB() { Name = "Joe" };

//      var child5 = new ChildB() { Name = "Sarah" };

//      var child6 = new ChildB() { Name = "Mike" };

        p.Children.Add(child1);

        p.Children.Add(child2);

        p.Children.Add(child3);

//      p.Children.Add(child4);

//      p.Children.Add(child5);

//      p.Children.Add(child6);

        var spec = new Specification<Parent>();

        Expression<Func<Parent, IList<ChildA>>> exp1 = x => x.Children.Where(c => c.Name == "Joe").ToList(); 

        LambdaExpression e = exp1;

        p.Children.Select<ChildA>(e);

    }

}

​

public abstract class Child {}

​

public class Parent

{

    public List<ChildA> Children;

}

​

public class Specification<T> where T : Parent

{

    public Expression<Func<T, IList<Y>>> CreateExpression<Y>(Expression<Func<T, IList<Child>>> toBeConverted)

    {

        return toBeConverted as Expression<Func<T, IList<Y>>>;

    }

}

​

public class ChildA : Child

{

    public string Name { get; set; }

}

​

public class ChildB : Child

{

    public string Name { get; set; }

}

​

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​

        //var spec = new Specification<Parent, ChildA>() ;

        //Type t1 = typeof(Specification<Parent,Child>);

        /*if (spec.GetType() == t1)

        {

            Console.WriteLine("Hello world");

        }

        else

        {

            Console.WriteLine($"spec type: {spec.GetType()}, t1 type: {t1}");

        }*/

        //Expression<Func<Parent, IList<Child>>> temp = x => x.Children;

        //MemberExpression me = Expression.Field(Expression.Constant(p), nameof(p.Children));

        //ParameterExpression x = Expression.Parameter(typeof(Parent), "x");

        //Expression.

        //Expression body = Expression.Call(

        //  x,

        //  ,

        //  Expression.Constant(p)

        //);