Select one field with linq entity framework

Question

User-1316533924 posted

Hi,

I trying to do something like this:

Select quantidade from AlimentoRefeicaos

And I have a object

 public class AlimentoRefeicao
    {
        public int Id { get; set; }
        public virtual Alimento Alimento { get; set; }
        public virtual Refeicao Refeicao { get; set; }
        public double Quantidade { get; set; }

    }

And in my service implementation i have a method:

  public List<AlimentoRefeicao> findAllQtd()
        {
            using (NutricaoContext mde = new NutricaoContext())
            {
                return mde.AlimentoRefeicao.Select(column => new AlimentoRefeicao
                    {Quantidade = column.Quantidade}).ToList();
            };
        }

when I invoke this method I get an exception

An exception of type 'System.NotSupportedException' occurred in EntityFramework.SqlServer.dll but was not handled in user code Additional information: The entity or complex type 'ControleNutricionalService.Models.AlimentoRefeicao' cannot be constructed in a LINQ to Entities query.

Answer 1

User1970566204 posted

Hi,

a) we can solve this one diffrent ways ....like suing  "DTO class"  or  "Anonymous"  or  "select Anonymous + inject into entity class"

1)  herewith  example for "select Anonymous + inject into entity class"

public List<AlimentoRefeicao> findAllQtd()
        {
            using (NutricaoContext mde = new NutricaoContext())
            {
                var anyms_AlimentoRefeicao= mde.AlimentoRefeicao.Select(
                             column => new 
                                       {Quantidade = column.Quantidade}).ToList();

                     
              way 1 : 
                       return anyms_AlimentoRefeicao.Select(
                             column => new AlimentoRefeicao 
                                       {Quantidade = column.Quantidade}).ToList();

              or 
              
           way 2 : 
            List<AlimentoRefeicao> result = new List<AlimentoRefeicao>();
              foreach(var currentAlimentoRefeicao in anyms_AlimentoRefeicao)
              {
                  result.add(new AlimentoRefeicao{ Quantidade = currentAlimentoRefeicao.Quantidade });
              }
              return result ;


            };
        }

Answer 2

User-1316533924 posted

asyed4u

Thank you very much.
It's worked very well.

Answer 3

User-1316533924 posted

Hi asyed4u

You can tell me if I can rename|alias the object Quantidade

Something like this:

public List<AlimentoRefeicao> findAllQtd()
        {
            using (NutricaoContext mde = new NutricaoContext())
            {
                var anyms_AlimentoRefeicao= mde.AlimentoRefeicao.Select(
                             column => new 
                                       {Quantidade = column.Quantidade}).ToList();
                return anyms_AlimentoRefeicao.Select(
                             column => new AlimentoRefeicao 
                                       {Quantidade AS Testing = column.Quantidade}).ToList();
           };
        }

Thank you

Answer 4

User1970566204 posted

Hi,

 

rename|alias the object Quantidade

 .. for display purpose.. ie like Header ?

use... System.ComponentModel.DataAnnotations. for reference

    way 1 : if you class not auto-genereated then..
    public class AlimentoRefeicao
    {
        public int Id { get; set; }
        public virtual Alimento Alimento { get; set; }
        public virtual Refeicao Refeicao { get; set; }
        [Display("Testing")] 
        public double Quantidade { get; set; }

    }
*************************

  way 2 : if you class auto-genereated then...

 public class AlimentoRefeicao
    {
        public int Id { get; set; }
        public virtual Alimento Alimento { get; set; }
        public virtual Refeicao Refeicao { get; set; }       
        public double Quantidade { get; set; }
    }

[MetadataType(typeof(AlimentoRefeicaoMetadata))]
public class AlimentoRefeicao 
{  
    
}

public class AlimentoRefeicaoMetadata
{  
        public int Id { get; set; }
        public virtual Alimento Alimento { get; set; }
        public virtual Refeicao Refeicao { get; set; }  
        [Display("Testing")] 
        public double Quantidade { get; set; }
}