Best way to create a map between two entities with a third one from another context

Question

Hi I'd like to create a map between two entities (source: User, target: UserInfosDto) while one member of the target DTO (UserItemPreference) needs info from a third entity inside another context.

public class UserInfosDto
{
    //public int UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }

    public UserItemPreferencesDto UserItemPreferences { get; set; }
}
public class UserItemPreferencesDto
{
    public bool SeeActuality { get; set; }
    public bool IsInEditorMode { get; set; }
}
public class User
{
    public string IdentityId { get; set; }
    //...
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
}

public class UserIdentity
{
    public string IdentityId { get; set; }
    //...  
    public bool SeeActuality { get; set; }
    public bool IsInEditorMode { get; set; }  
}

User and UserIdentity come from different databases but have a common property IdentityId. I thought about using ITypeConverter in which I would inject the UserIdentity dbContext. Problem is that I can't find a way to use ITypeConverter on one member only.

Answer 1

Use an IValueResolver instead, which allows to resolve separate members instead of full types.

For your case above it will look like

public class UserItemPreferencesResolver
    : IValueResolver<User, UserInfosDto, UserItemPreferencesDto>
{
    private readonly UserEntityDbContext _dbContext;

    public UserItemPreferencesResolver(UserEntityDbContext dbContext)
    {
        _dbContext = dbContext;
    }

    public UserItemPreferencesDto Resolve(
        User source,
        UserInfosDto destination,
        UserItemPreferencesDto destinationMember,
        ResolutionContext context
        )
    {
        UserItemPreferencesDto preferences = /* resolve from _dbContext (and transform) */
        return preferences;
    }
}

Your create the mapping via

CreateMap<User, UserInfosDto>()
    .ForMember(
        dest => dest.UserItemPreferences, 
        opt => opt.MapFrom<UserItemPreferencesResolver>()
    );