How to convert parent collection object to child collection object without looping in C#?

Question

I have following object structure where B is derived from A and I am getting input as List<A> with lots of records. I want to convert thatList<A> to List<B> with easy steps (without looping). What is the best way to achieve the same.

Note: I don't want to use AutoMapper.

    public class A
    {
        public A() { }
        public virtual string Name
        {
            get;
            set;
        }
    }

    public class B : A
    {
        public B()
            : base()
        {
        }
        private string _name;
        public override string Name
        {
            get
            {
                return _name;
            }
            set
            {
                _name = string.Concat("Hello ", base.Name);
            }
        }

        public string Id
        {
            get { return "101"; }
        }
    }

If `List` actually contains objects of only type `B`, then you can just use LINQ Cast `List listB = listA.Cast().ToList()`. — Yeldar Kurmangaliyev, May 24 '17 at 04:25
I already tried that its giving - Unable to cast object of type 'A' to type 'B'. exception. — Sumit Deshpande, May 24 '17 at 04:27
Try creating the list of B and adding the range of listA.Cast(). — russelrillema, May 24 '17 at 04:29
Tried your suggestion - var listA = new List { new A { Name = "John" }, new A { Name = "Peter" }, new A { Name = "Julia" } }; List listB = new List().AddRange(listA); Not working — Sumit Deshpande, May 24 '17 at 04:34
@SumitDeshpande What is the reason you want to create list of `Base Class` and than get list of `Derived Class`? — Samvel Petrosov, May 24 '17 at 04:38
I am getting List of Base class as Input and I want to build my derived class by massaging few Base class properties. E.g. Name property, suppose if Base has Name=”John” then in B class I want “Hello John” that’s the difference. — Sumit Deshpande, May 24 '17 at 04:49
You can cast (B)ear as (A)nimal, but not (A)nimal as (B)ear, because an animal is not necessarily a bear. You need to do `List ListA = new List();` then you can properly cast `ListA` to `List`. Otherwise, you need to convert the `A` into `B` explicitly. — kurakura88, May 24 '17 at 05:03

score 2 · Accepted Answer · answered May 24 '17 at 04:54

2

You can do this by declaring constructor for class B from class A in this way:

public B(A a):base()
{
    this._name = a.Name;
}

And than do this:

var listA = new List<A> { new A { Name = "John" }, new A { Name = "Peter" }, new A { Name = "Julia" } }; 
List<B> listB = listA.Select(x=> new B(x)).ToList();

answered May 24 '17 at 04:54

Samvel Petrosov

7,580
2
22
46

I actually don't want to use loop but I think your solution is correct we have to run linq query to achieve the same. – Sumit Deshpande May 24 '17 at 17:03

score 0 · Answer 2 · answered May 24 '17 at 04:30

0

Based on the comments this is the output, though I still don't really understand the point.

        List<A> thisIsA = new List<A>();

        thisIsA.Add(new B());

        List<B> thisIsB = new List<B>();
        thisIsB.AddRange(thisIsA.Cast<B>());

answered May 24 '17 at 04:30

russelrillema

452
7
14

this will throw Exception if in `thisIsA` exists instance of `class A` – Samvel Petrosov May 24 '17 at 04:31
It will which is why I say I don't full understand the point but based on the OP thisIsA in this context will never hold an instance of class A – russelrillema May 24 '17 at 04:34
look at his example in the comments thisIsA has only instances of A – Samvel Petrosov May 24 '17 at 04:36
I don't know if this post would be of any help https://stackoverflow.com/a/16534314/1521076 – ccStars May 24 '17 at 04:43

How to convert parent collection object to child collection object without looping in C#?

2 Answers2