How to deal with relational entity mapping in AutoMapper? - entity-framework

Question

Our Entity model has navigation properties:
public class Course
{
public Guid Id { get; set; }
...
public Guid InstructorId { get; set; }
public virtual Instructor Instructor { get; set; }
public virtual ICollection<Instructor> Coinstructors { get; set; }
}
That is, a course have one instructor and multiple coinstructors.
My view model has the id's of those instructors.
public class CourseCreateModel
{
...
public InstructorModel Instructor { get; set; }
public IEnumerable<InstructorModel> Coinstructors { get; set; }
}
The InstructorModel contains the Id:
public class InstructorModel
{
public Guid Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
To make the data transfer from our DTO CourseCreateModel into the domain model Course, we can map the instructor easily because there is a InstructorId in the domain model:
Mapper.CreateMap<CourseCreateModel, Course>()
.ForMember(dest => dest.InstructorId, opts => opts.MapFrom(src => src.Instructor.Id))
...;
But how to map Coinstructors? We can get an array of coinstructor's id. But how to do the mapping?

Answer 1

I believe you have two options:
Option nr. 1 :
.ForMember(c=>c.Coinstructors,op=>op.MapFrom(v=>v.Coinstructorids.Select(c=>new Instructor(){Id=c})))
where Coinstructorids = List<int>();
Option nr. 2:
Create an custom resolver:
public class CustomConvert : ValueResolver<IList<int>, IList<Instructor>>
{
protected override string ResolveCore(IList<int> source)
{
string result = new List<Instructor>();
foreach (var item in source)
{
result.Add(new Instructor() {Id = item});
}
return result;
}
}
and the use it :
.ForMember(c => c.Coinstructors, op => op.ResolveUsing<CustomConvert>().FromMember(c => c.Coinstructorids));
where Coinstructorids = List<int>();