How to pass context values to Automapper Map?

Question

I using Automapper. I have two classes: TypeA with single property; TypeB with two properties, one of them have private setter and value for this property is passed via constructor. TypeB have no default constructor.

Question: is it possible to configure Automapper to convert TypeA to TypeB.

public class TypeA
{
    public string Property1 { get; set; }
}

public class TypeB
{
    public TypeB(int contextId)
    { ContextId = contextId; }

    public string Property1 { get; set; }

    public int ContextId { get; private set; }
}

public class Context
{
    private int _id;

    public void SomeMethod()
    {
        TypeA instanceOfA = new TypeA() { Property1 = "Some string" };

        // How to configure Automapper so, that it uses constructor of TypeB 
        // and passes "_id" field value into this constructor?

        // Not work, since "contextId" must be passed to constructor of TypeB
        TypeB instanceOfB = Mapper.Map<TypeB>(instanceOfA);

        // Goal is to create folowing object
        instanceOfB = new TypeB(_id) { Property1 = instanceOfA.Property1 };
    }
}

Answer 1

You can use one of the ConstructUsing overloads to tell AutoMapper which constructor should it use

TypeA instanceOfA = new TypeA() { Property1 = "Some string" };
_id = 3;            

Mapper.CreateMap<TypeA, TypeB>().ConstructUsing((TypeA a) => new TypeB(_id));    
TypeB instanceOfB = Mapper.Map<TypeB>(instanceOfA);

// instanceOfB.Property1 will be "Some string"
// instanceOfB.ContextId will be 3

As an alternative solution you can create your TypeB by hand the AutoMapper can fill in the rest of the properties":

TypeA instanceOfA = new TypeA() { Property1 = "Some string" };
 _id = 3;            

Mapper.CreateMap<TypeA, TypeB>();

TypeB instanceOfB = new TypeB(_id);
Mapper.Map<TypeA, TypeB>(instanceOfA, instanceOfB);

// instanceOfB.Property1 will be "Some string"
// instanceOfB.ContextId will be 3