Question

I’d like to be able to project/map properties from either of 2 child classes.
Imagine a parent class that has 2 child classes, either of 1 which points to a child class. Each child class must map to properties on the model class.

However, if child class 1 is null then it shouldn’t map across to the model it should map class 2 properties instead.

It’s like what I want to do here except do it across a whole class of properties rather than 1 property:

Conditonal projection

I was hoping I don’t have to create a CustomResolver for each class property and whether there is a better way of achieving this. Imagine that the child classes have 10 identical properties each, all I want to do is switch the map depending on which child class is populated.

public class Message
{
     public string Comment { get; set; }
     public Inbound? InboundMessage { get; set; }
     public Outbound? OutboundMessage { get; set; }
}

public class Inbound
{
     public string Body { get; set; }
    // 10 properties...
}

public class Outbound
{
     public string Body { get; set; }
    // 10 properties...
}


public class MessageModel
{
     public string Comment { get; set; }
     public string Body { get; set; }
    // 10 properties....
}

Answer 1

Surprised no-one had an answer to this so answered myself by the time I worked out what to do.

If you have the need to conditionally map properties depending on whether a child class is populated or not, or any other logic for the whole class for that matter, then you can use a TypeConverter.

Inside the TypeConverter, you test the source parameter in the ConvertCore function, and then call Mapper.Map on the correct source to pass the child class properties out to the model.

The return from mapper can be then returned back out which will be the destination.
I never realised that you can still call Mapper.Map() even in the TypeConverter.