Convert DbSetT to different data type in EF - Linq

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Convert DbSetT to different data type in EF - Linq

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#2 by (0 votes)

1

I'm working on an expression Linq in which I get an object of DBContext , and I want to convert it into an object of ViewModel

My ViewModel receives as parameter an object obtained from DBContext to work the information and return it completely

public class Obj1 // Objeto obtenido de la base de datos
{
   public int id { get; set; }
   public string Param { get; set; }
   public string Param2 { get; set; }
   public string Random { get; set; }
}

public class Obj2 //ViewModel
{
   public string ParamFormateado { get; set; }
   public string  Random { get; set; }

   public Obj2(Obj1 parametro)
   {
     ParamFormateado = parametro.Param + parametro.Param2;
     Random = parametro.Random;
   }

}

In essence, the second class works on the parameters of the first and formats them and then moves to a view.

What I'm trying to do is get a Obj2 from a base from a DBContext that has Obj1

I try something like this

Obj2 objeto = db.Obj1.Where(x => x.id == "0").Select(x => new Obj2(x)).FirstOrDefault();

Is it possible to make a query Linq similar to the one I am proposing? since otherwise, I end up having expressions Linq extremely long to format this information, but what would be the best alternative in these cases?

Greetings and thanks for taking the time to read!

c# linq asp.net-mvc-5 linq-to-sql

asked by Juan Salvador Portugal 27.06.2018 в 14:29

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2 answers

0

It is not necessary to execute Where and then FirstOrDefault to obtain the first element through the collection

For that, execute FirstOrDefault and pass the condition in this method directly

Obj2 objeto = db.Obj1.FirstOrDefault(x => x.id == "0").Select(x => new Obj2(x));

Greetings

answered by 27.06.2018 в 15:09

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score 1 · Accepted Answer

In Stackoverflow in English a Tim Schmelter answered my question , I translate your answer so you can be useful to other people.

You can not do it, since it only supports constructors without parameters, but you can do it with Linq-To-Objects , which can be forced with AsEnumerable
Obj2 objeto = db.Obj1
   .Where(x => x.id == "0")
   .AsEnumerable()   // <--- here
   .Select(x => new Obj2(x))
   .FirstOrDefault();
Therefore, the Where will be executed in the database, but the   rest, will be executed with Linq-To-Objects

For more information, you can see this post in the Jon's blog   Skeet