C# ASP.NET MVC: How to get list of elements by id column returned from a list in Entity Framework

Question

I have to create 2 lists and i am looking for the best practice and eventually oneline syntax!

I am using Entity Framework and I have 3 tables:

public class Position 
{
    public int ID { get; set; }
    public string Name { get; set; }
}

public class Training 
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Association 
{
    public int Id { get; set; }
    public Impact Impact { get; set; }

    public int TrainingId { get; set; }
    public virtual Training Training { get; set; }
    public int PositionId { get; set; }
    public virtual Position Position { get; set; }
}

public enum Impact 
{
    Optional,
    Mandatory
}

I have to select all the training which are mentioned in Association table as mandatory or optional (I mean that must have the column Impact fill with Impact.Optional) and the PositionId is the one that I give it through a parameter or something!

How can I do that?

Is this what you need? var result = db.Asociation.Where(x => x.Impact == Impact.YOUR_IMPACT && PositionId == YOUR_ID); — Matt
– Matt, Commented Jul 2, 2019 at 11:11
@Matt almost yes and with this, how I can get a collection of Training! Your syntax filters the right "associations" and I want to use TrainingId to take the training list! — Adrian Panaintescu
– Adrian Panaintescu, Commented Jul 2, 2019 at 11:22

Michał Turczyn · Accepted Answer · 2019-07-02 11:27:45Z

1

Try this

public List<Training> GetOptionalTrainings(int positionId)
{
  _context.Associations
    .Where(a => a.Impact == Impact.Optional && a.PositionId == positionId)
    .Select(a => a.Training)
    .ToList();
}

answered Jul 2, 2019 at 11:27

Michał Turczyn

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Comments

Zakos · Accepted Answer · 2019-07-02 11:55:18Z

0

note that your relations are 1-1 ,Association will always have a Training , if you want a 0 or 1 relation you can change public int TrainingId to public int? TrainingId

updated

edited Jul 2, 2019 at 11:55

answered Jul 2, 2019 at 11:49

Zakos

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