using System;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Dynamic.Core;

public class Program

{

    public static void Main()

    {

        // Make a list of Person

        List<Person> people = new List<Person>();

        people.Add(new Person(){

            Id = 999,

            FirstName = "Firsty",

            LastName = "Lasty",

            Address = new Address(){

                Id = 888,

                AddressLine1 = "123 Road St.",

                AddressLine2 = "Placetown",

                City = "BigCity",

                Postcode = "A12 3BC"

            }

        });

        IQueryable<Person> peopleQueryable = people.AsQueryable();

        // The dynamic linq string with projection to return only Person.Id, Person.FirstName and person.Address

        // The results will include all properties of Address.

        // QUESTION: How to project the properties of Address? For example, just the Id and City properties 

        string dynamicSelect = "new Person(Id, FirstName, Address)";

        IEnumerable<Person> result = (IEnumerable<Person>)peopleQueryable.Select(dynamicSelect);

        foreach(var person in result)

        {

            // LastName is not included in the project so is null. As expected

            Console.WriteLine(string.Format("Id: {0}, FirstName: {1}, LastName: {2}", person.Id, person.FirstName ?? "null", person.LastName ?? "null"));

            // All Address properties are populated

            var address = person.Address;

            Console.WriteLine(string.Format("Id:{0}, AddressLine1:{1}, AddressLine2: {2}, City: {3}, Postcode:{4}", address.Id, address.AddressLine1 ?? "null", address.AddressLine2 ?? "null", address.City ?? "null", address.Postcode ?? "null"));

        }

    }

}

​

public class Person

{

    public int Id {get;set;}

    public string FirstName {get;set;}

    public string LastName {get;set;}

    public Address Address {get;set;}

}

​

public class Address

{

    public int Id {get;set;}

    public string AddressLine1 {get;set;}

    public string AddressLine2 {get;set;}

    public string City {get;set;}

    public string Postcode {get;set;}

}