AutoMapper - Map and add elements to list conditionally

Question

I have a unique requirement when mapping some elements using AutoMapper.

I am not finding any effective solution with built scenarios:

1. I want to add phone number details to the contacts list if the phone number is not null.
2. I want to add email address details to the contacts list if the email is not null.

CreateMap<UserModel, UserDefinition>()
              .ForMember(d => d.Id, o => o.Ignore()) 
              .ForMember(d => d.UserName, o => o.MapFrom(s => s.Username))
              .ForMember(d => d.Contacts, o =>  
                  new List<UserContactDefinition>()
                  {
                      o.MapFrom(s => !string.IsNullOrWhiteSpace(s.PhoneNumber) ?
                      new UserContactDefinition
                      {
                          Type = ContactType.Phone,
                          IsPrimary = true,
                          Label = s.PhoneType,
                          Value = s.PhoneNumber
                      }: null,
                      o.MapFrom(s => !string.IsNullOrWhiteSpace(s.ContactEmail) ?
                       new UserContactDefinition
                       {
                           Type = ContactType.Email,
                           IsPrimary = true,
                           Label = s.EmailType,
                           Value = s.Email
                       }: null
                  }                   
              ); 

This code is not working and I don't want to add empty elements if there is no value.

Any leads to this?

Answer 1

For your scenario, you need the Custom Value Resolver to map the destination member for the Contacts property.

1. Implement UserContactDefinitionListResolver custom value resolver.

public class UserContactDefinitionListResolver : IValueResolver<UserModel, UserDefinition, List<UserContactDefinition>>
{
    public List<UserContactDefinition> Resolve(UserModel src, UserDefinition dst, List<UserContactDefinition> dstMember, ResolutionContext ctx)
    {
        dstMember = new List<UserContactDefinition>();
        
        if (!string.IsNullOrWhiteSpace(src.PhoneNumber))
            dstMember.Add(new UserContactDefinition
            {
                Type = ContactType.Phone,
                IsPrimary = true,
                Label = src.PhoneType,
                Value = src.PhoneNumber
            });
            
        if (!string.IsNullOrWhiteSpace(src.ContactEmail))
            dstMember.Add(new UserContactDefinition
            {
                Type = ContactType.Email,
                IsPrimary = true,
                Label = src.EmailType,
                Value = src.ContactEmail
            });
        
        return dstMember;
    }
}

2. Add mapping configuration/profile for the member Contacts to use the UserContactDefinitionListResolver.

CreateMap<UserModel, UserDefinition>()
    .ForMember(d => d.Id, o => o.Ignore())
    .ForMember(d => d.UserName, o => o.MapFrom(s => s.Username))
    .ForMember(d => d.Contacts, o => o.MapFrom(new UserContactDefinitionListResolver()));

Demo @ .NET Fiddle