AutoMapper - Retrieve a different field from a linked source table than the one that links it - automapper

Question

I have the following table structure that mixes legacy fields with an updated schema:
Coaster
Id (Int)
ParkId (Int)
Park
Id (int)
UniqueId (Guid)
So, the Coaster and Park tables are linked using the Park.Id field. The UniqueId field is not currently used in the old schema. We are migrating to a clean DB using AutoMapper, and this new schema looks like this:
Coaster
Id (Int)
ParkId (Guid)
Park
Id (Guid)
The problem I am having is doing this using AutoMapper. I've been experimenting with this code:
private ModelMapper()
{
Mapper.Initialize(x =>
{
x.AddProfile<ConvertersMappingProfile>();
});
}
// This is the part that I'm trying to work out
public ConvertersMappingProfile()
{
CreateMap<Park, NewSchema.Park>()
.ForMember(dst => dst.Id, map => map.MapFrom(src => src.ParkId));
}
In the new schema, the Park table's Id matches the old schema's UniqueId.
My question is: Because in the old schema there is no direct link to the UniqueId value of the Park table, how to do I get that value to map to the new schema using the Coaster.ParkId field to Park.Id field mapping?

Answer 1

I used a custom resolve to fix the problem. So I created my resolver, which pulls up a list of the items in the database (which is typically pretty small) to get all the values from the table I need, and retrieves the value. (Pre-refactored code):
public class ParkResolver : IValueResolver<Original.Park, New.Park, string> {
public string Resolve(Original.Park source, New.Park dest, string destMember, ResolutionContext context) {
List<Original.Park> list = new List<Original.Park>();
using (IDbConnection con = new SQLiteConnection(#"Data Source=C:\Users\Me\Documents\Parks.sql;")) {
con.Open();
list = con.Query<Original.Park>($"SELECT * FROM Parks WHERE Id = {source.ParkId}").ToList();
con.Close();
}
return list.FirstOrDefault().UniqueId;
}
}
And I call my custom resolver for the tables I am mapping:
CreateMap<Original.Park, New.Park>()
.ForMember(dst => dst.ParkId, map => map.MapFrom(new ParkResolver()));
Hopefully that will help someone else.