Automapper and Linq with joined tables, populating ViewModel properties

Question

Having just figured out how to populate my ViewModel from a model using Automapper, I am now onto the next challenge – populating the ViewModel properties from a joined table.

The image below depicts my simple database.

enter image description here

My ViewModel class is defined as:

public class PersonViewModel
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Nullable<int> Age { get; set; }
    public Nullable<int> SuffixId { get; set; }
    public string PersonStatus { get; set; }
    public string PersonPreference { get; set; }

    public virtual Suffix Suffix { get; set; }
}    enter code here

Note the additional fields of PersonStatus and PersonPreference that will come from joining PersonInfo to Person. Here is the code I use to instantiate my mapping configuration:

        Mapper.CreateMap<PersonViewModel, Person>();
        Mapper.CreateMap<Person, PersonViewModel>();

And now the code to populate the ViewModel

        List<PersonViewModel> persons = null;
        using (var context = new DemoEntities())
        {
            persons = (from p in context.People.AsEnumerable()
                       join i in context.PersonInfoes on p.Id equals i.PersonId
                    select Mapper.Map<PersonViewModel>(p)).ToList();
            return persons;
        }

How would I populate the two joined properties (PersonStatus and PersonPreference) from this setup?

Thanks in advance!

Why are you joining PersonInfoes at all? EF will handle this for you automatically and automapper will map it. — Scottie, Nov 27 '13 at 22:44
First a few questions: why the `AsEnumerable()` and how do you get one (of many) `PersonInfo`s? — Gert Arnold, Nov 27 '13 at 22:45
Well, first, it's just a simple example I threw together so that I could pose the question. But Scottie, you say that AM will do it automatically. Can you elaborate? btw, person to personinfo is actually 1 to 1, not 1 to many. I'm trying to simulate a business rule we have on another system with this example. Gert, I was running into an error without the AsEnumerable(), I found this link which helped me resolve it: http://stackoverflow.com/questions/14770941/linq-and-automapper — gilpach, Nov 27 '13 at 22:55

score 4 · Accepted Answer · edited May 23 '17 at 11:48

AutoMapper can automatically flatten an object structure if the source and target classes meet some requirements.

The source class, the class that the mapping starts from, should have reference property to the related class. In you case: Person.PersonInfo (1:1, but n:1 will also work).¹
The target class should contain property names that allow AutoMapper to resolve the property path to the referenced object. in your case: PersonViewModel.PersonInfoStatus, so AutoMapper will see that there's a property PersonInfo in the source object and a property Status in the referenced object.

If you've got these things in place, you can do

persons = context.People.Project().To<PersonViewModel>().ToList();

The Project().To syntax is a relatively new API that allows working on IQueryables. For more details see Does AutoMapper support Linq?.

You will see that this sends a JOIN query to the database.

¹AutoMapper can also aggregate/flatten associated collections, but that's a different chapter.

Automapper and Linq with joined tables, populating ViewModel properties

1 Answers1