I do not understand how EF5 dbContext.Entry(entity).Reload() method is supposed to work?

Question

In this example :

using System;
using System.Collections.Generic;
using dbModel;
using System.Linq;
using System.Data.Entity.Infrastructure;


namespace WinApp
{
    public partial class Form1 : Form
    {
        private dbEntities dbc;
        public IQueryable<ARTIKLI> art;
        public IQueryable<ART_GRUPE> grp;

        public Form1()
        {
            InitializeComponent();
            dbc = new dbEntities();            
        }


        private void GetData()
        {
            art = from a in dbc.ARTIKLIs
                        select a;

            grp = from g in dbc.ART_GRUPE
                        select g;

            artikliBindingSource.DataSource = art.ToList();
            artGrupeBindingSource.DataSource = grp.ToList();
        }


        private void Form1_FormClosing(object sender, System.Windows.Forms.FormClosingEventArgs e)
        {
            dbc.SaveChanges();
        }


        private void loadData_Click(object sender, EventArgs e)
        {
            this.GetData();  
        }


        private void refresh_Click(object sender, EventArgs e)
        {

            dbc.Entry(grp).Reload();
            artGrupeBindingSource.ResetBindings(false);
        }

    }
}

everything builds OK. But when I run and click Refresh button I get error :

The entity type DbQuery`1 is not part of the model for the current context

I am just trying to refresh data from store for grp entity instance using DbContext. I know I can convert DbContext into ObjectContext and then use Refresh method, but it should be possible to do the same with DbContext.Entry(entity).Reload();

Can someone explain my mistakes in the code above?

Solution

If dbEntities is a DbContext, then you are talking about doing, effectively dbc.Entry<ART_GRUPE>().Reload();, to discard all changes and reload the entities, not reloading your query. However, this does not exist. You can discard any changes made to a single entity using the dbc.Entry<ART_GRUPE>(myEntity).Reload() ("MSDN - DbEntityEntry<TEntity>.Reload Method").

DbContext is not meant to be long lived, you are meant to use it for your query, then get rid of it. If you want to cast it to an object context, you could try:

var ctx = ((IObjectContextAdapter)db).ObjectContext;
ctx.Refresh();

This may not be what you need. It also doesn't remove entities deleted from the db from your context, and it doesn't always refresh relationships. You may be better off getting rid of the context and loading it again:

private void GetData()
{
    // you could wrap this in a using statement, though that isn't necessary
    using (var dbc = new dbEntities())
    {
        art = from a in dbc.ARTIKLIs
            select a;

        grp = from g in dbc.ART_GRUPE
            select g;

        artikliBindingSource.DataSource = art.ToList();
        artGrupeBindingSource.DataSource = grp.ToList();
    }
}
private void refresh_Click(object sender, EventArgs e)
{
    GetData();
    // not sure you need this next line now, but you should test
    artGrupeBindingSource.ResetBindings(false); 
}

The problem this may cause you is that you are making changes to ARTIKLIs and trying to track them. For that you could use something like the following to save changes, and do not reload your ARTIKLIs each time:

private void GetData(bool loadArtikli = true)
{
    // you could wrap this in a using statement, though that isn't necessary
    using (var dbc = new dbEntities())
    {
        if (loadArtikli)
        {
            art = from a in dbc.ARTIKLIs
                select a;
        }

        grp = from g in dbc.ART_GRUPE
            select g;

        artikliBindingSource.DataSource = art.ToList();
        artGrupeBindingSource.DataSource = grp.ToList();
    }
}
private void refresh_Click(object sender, EventArgs e)
{
    GetData(false);
}

public static void UpdateARTIKLI(ARTIKLI item)
{
  using (var dbc = new dbEntities())
  {
    if (item.Id > 0)
    { // update existing ones
      var dbitem = context.ARTIKLI 
        .Find(item.Id);

      context.Entry(dbItem)
        .CurrentValues
        .SetValues(item);
    }
    else
    { // deal with new ones
      context.ARTIKLI.Add(item);
    }

    context.SaveChanges();
  }
}

Comments

[Wiktor Zychla]

What instance is supposed to be?

[Andy Brown]

@WiktorZychla. Corrected, thank you. instance was a figment of my lack of coffee and sleep.

[Wiktor Zychla]

Still wrong perhaps. Entry method requires instance parameter.

[Andy Brown]

@WiktorZychla. Coffee acquired. Answer rewritten!

[EmirZ]

This works, and I am doing exactly this in my project... but the need to cast DbContext to ObjectContext is very much annoying. I thought that it is I who does not understand the DbContext well, but is seems that DbContext really isn't equipped with this simple functionality !?!?

[Andy Brown]

@Virtuo. I think it just isn't meant to be kept hanging around or you chew up the connection pool to the database.

[EmirZ]

Thank you Andy! It seems I will have to reStudy EF5 and DbContext.

[Andy Brown]

@Virtuo. Have a look at this as well: Entity Framework 4.1 DbSet Reload. Have also added a comment in my answer about casting to ObjectContext