map array of list using automapper

Question

I'm trying to map an array of objects containing source classes, which has to be mapped destination classes.

class A
{
        public string Id { get; set; }
        public string Name { get; set; }
        public string Url { get; set; }
        public string Details { get; set; }
        public string Image { get; set; }
        public string Decription{ get; set;}
 }

class B
{
 public string Id { get; set; }
 public string Name { get; set; }
 public List<C> { get; set; }
}

class C{
  public string Url { get; set; }
  public string Details { get; set; }
  public string Image { get; set; }
  public string Decription{ get; set;}
}

I need to map from List of class B to List class A using auto mapper Kindly help

If there are three B objects, each of which contains a List of four C objects, how many A objects are you expecting to receive as a result of the mapping? — mjwills
– mjwills, Commented Aug 26, 2017 at 11:45
Possible duplicate of Possible to use AutoMapper to map one object to list of objects? — Joshua K
– Joshua K, Commented Aug 26, 2017 at 11:53
I didn't liked the explanation in the duplicate question, so I tried to explain it a little bit better. I hope I achieved this and it helps you to understand the way you have to go. — Joshua K
– Joshua K, Commented Aug 26, 2017 at 12:28

Joshua K · Accepted Answer · 2017-08-26 12:27:41Z

It's simple. You have to map the information in two steps.

First let's simplify your example:

class A {
    public string AttrB { get; set; }
    public string AttrC { get; set; }
}
class B {
    public string AttrB { get; set; }
}

class C {
    public string AttrC { get; set;}
}

To create one object of A from B and C you have to create two maps and use them after each other:

Mapper.CreateMap<B, A>();
Mapper.CreateMap<C, A>();

var c = new C { AttrC = "AttrCValue" };
var b = new B { AttrB = "AttrBValue" };
var a = Mapper.Map<A>(b); // a with the attribute values of b
Mapper.Map(c, a); // map the attribute values of c also into a

I think nothing new for you. But now comes the tricky part. It works with the same principle:

class A {
    public string AttrB { get; set; }
    public string AttrC { get; set; }
}
class B {
    public string AttrB { get; set; }
    public List<C> AttrBList { get; set; }
}

class C {
    public string AttrC { get; set;}
}

We need another map and a custom converter:

Mapper.CreateMap<B, A>();
Mapper.CreateMap<C, A>();
Mapper.CreateMap<B, IEnumerable<A>>().ConvertUsing<BConverter>();

class BConverter : ITypeConverter<B, IEnumerable<A>> {
    public IEnumerable<A> Convert(ResulutionContext ctx) {
        B b = (B)ctx.SourceValue;
        foreach(var aFromC in b.AttrBList.Select(c => Mapper.Map<A>(c))) { // map c attributes into an a object and return it (through Select it's a mapping for all items of the list AttrBList)
            Mapper.Map(b, aFromC); // push the attribute values from b to the aFromC object. Because this is inside the loop, it happens for every Item in the AttrBList array
            yield return aFromC;
        }
    }
}

Now you can use it:

var allAObjects = Mapper.Map<IEnumerable<A>>(listOfBObjects);

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