Clever Geek Handbook

Outer Joins and Linq

So I have the following code:

  return from a in DBContext.Acts
         join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
         from artist in art.DefaultIfEmpty()

         select new Shared.DO.Act
         {
             ID = a.ID,
             Name = a.Name,
             Artist = new Shared.DO.Artist
             {
                 ID = artist.ID,
                 Name = artist.Name
             },
             GigId = a.GigID
         };

This loads the action object and adapts it from the linq object to the act object of the domain object.

As you can see, I've defined an outer artist connection to interact with.

I did this because I always need an act, whether or not it has an artist.

This works really well if the act actually has an artist.

If it doesn't, then the code dies. This is the culprit:

 Artist = new Shared.DO.Artist
          {
              ID = artist.ID,
              Name = artist.Name
          },

If I remove it, it will be fine. Can I do what I am trying to do?

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3 answers 


           Artist = new Shared.DO.Artist
           {
               ID = artist == null ? Guid.NewGuid() : artist.ID,
               Name = artist == null ? string.Empty : artist.Name
           }


Alternatively, add a constructor to Shared.DO.Artist that displays the Linq Artist view. The constructor can check for null and do all the initialization.

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Actually ... this seems like the best answer for me ....



Artist = artist == null ? null : new Shared.DO.Artist
                    {
                       ID =  artist.ID,
                       Name = artist.Name
                    },
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You want to create a new object by calling the constructor. Remove Artist = and then replace {} with ().

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