How to select multiple columns in entity framework?

Question

In my first question I didn't explain well. But now I need to select some columns from a entity framework class.

var Muestra = Cecytec.asignatura.Select(Z => new asignatura { nombre = Z.nombre, horasPorSemana = Z.horasPorSemana, nivel = Z.nivel, unidades = Z.unidades }).ToList();

From my class(table) "asignatura" I have this:

public partial class asignatura
{
    public asignatura()
    {
        this.criterioevaluacion = new HashSet<criterioevaluacion>();
        this.evaluacion = new HashSet<evaluacion>();
        this.examen = new HashSet<examen>();
        this.alumno = new HashSet<alumno>();
        this.horario = new HashSet<horario>();
        this.profesor = new HashSet<profesor>();
    }

    public int idAsignatura { get; set; }
    public Nullable<int> horasPorSemana { get; set; }
    public string nombre { get; set; }
    public Nullable<int> nivel { get; set; }
    public Nullable<int> unidades { get; set; }
    public int semestres_idsemestres { get; set; }

    public virtual semestres semestres { get; set; }
    public virtual ICollection<criterioevaluacion> criterioevaluacion { get; set; }
    public virtual ICollection<evaluacion> evaluacion { get; set; }
    public virtual ICollection<examen> examen { get; set; }
    public virtual ICollection<alumno> alumno { get; set; }
    public virtual ICollection<horario> horario { get; set; }
    public virtual ICollection<profesor> profesor { get; set; }
}

And I want to show: 'nombre', 'horasPorSemana', 'nivel', 'unidades' and 'calificacion'

Note: 'calificacion' is in another class

public partial class evaluacion
{
    public int unidad { get; set; }
    public Nullable<double> calificacion { get; set; }
    public Nullable<int> inasistencia { get; set; }
    public string observaciones { get; set; }
    public int asignatura_idAsignatura { get; set; }

    public virtual asignatura asignatura { get; set; }
}

Nick Coad · Accepted Answer · 2021-12-06 07:47:10Z

2

In your projection you're projecting to an entity from your database. What you need to do is one of two options:

Project to an anonymous class

var Muestra = Cecytec .asignatura .Select(Z => new { nombre = Z.nombre, horasPorSemana = Z.horasPorSemana, nivel = Z.nivel, unidades = Z.unidades, evaluacion_calificacion = Z.evaluacion.Select(e => e.calificacion) }) .ToList();

This will give you a list of anonymous objects stored in the variable Muestra with each containing an IEnumerable of calificacion values from the evaluacion table.

Project to a predefined class with the properties you need

This is similar to the above but you just define a class to hold the properties.

public class ProjectionResult
{
    public string nombre { get; set; }
    public Nullable<int> horasPorSemana { get; set; }
    public Nullable<int> nivel { get; set; }
    public Nullable<int> unidades { get; set; }
    public IEnumerable<Nullable<double>> evaluacion_calificacion { get; set; }
}

Then run your projection like this:

var Muestra = Cecytec
    .asignatura
    .Select(Z => new ProjectionResult
        {
            nombre = Z.nombre,
            horasPorSemana = Z.horasPorSemana,
            nivel = Z.nivel,
            unidades = Z.unidades,
            evaluacion_calificacion = Z.evaluacion.Select(e => e.calificacion)
        })
    .ToList();

This will give you a list of ProjectionResult objects stored in the variable Muestra with each containing an IEnumerable of calificacion values from the evaluacion table.

edited Dec 6, 2021 at 7:47

answered Aug 25, 2017 at 2:13

Nick Coad

3,7145 gold badges39 silver badges64 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Hector Miguel Soto Over a year ago

OMG! the second works! Thank you Mr Member from Stackoverflow

Nick Coad Over a year ago

@GertArnold correct, thank you. I've modified the answer.

Hector Miguel Soto · Accepted Answer · 2017-08-25 04:37:27Z

Your answer is OK but it do not show

evaluacion_calificacion = Z.evaluacion.Select(e => e.calificacion)

Always null, to fix that I did this:

public class ProjectionResult { public Nullable<int> horasPorSemana { get; set; }
    public string nombre { get; set; }
    public Nullable<int> nivel { get; set; }
    public Nullable<int> unidades { get; set; }
    //public virtual IEnumerable<Nullable<double>> evaluacion_calificacion { get; set; }
    public Nullable<double> calificacion { get; set; } }

And to the query change the last line:

 var Muestra = Actualmente.Select(Z => new ProyeccionAcademica
                {
                    nombre = Z.nombre,
                    horasPorSemana = Z.horasPorSemana,
                    nivel = Z.nivel,
                    unidades = Z.unidades,                        
                    calificacion = Z.evaluacion.First(Find => Find.asignatura_idAsignatura == Z.idAsignatura).calificacion                        
                    }).ToList();

But thanks for your quick answer!!!

Collectives™ on Stack Overflow

How to select multiple columns in entity framework?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related