How to do a .Find on an inheritance entity?

Question

I have two entities in this case : Membre inherits from Utilisateur .

I have a ListView so I want to show the Membre that is currently showed. The line that is generating the error is

Membre lemembre = (lecontexte.Set<Membre>().Find(membrealecran.Pseudo));

All I want this line to do is do a .Find(membrealecran.Pseudo) ... But I can't use the .Find on Set<Membre> .

It generates an System.ArgumentException and Data.EntitySqlException. It says Int32 and String are incompatible for the operation...

I can do a .Find on Utilisateur , but not on Membre . Why? How could I do a Find on Membre ?

protected void lvInscription_ItemDataBound(object sender, ListViewItemEventArgs e)
{
    using (modele_vivo_amoreContainer lecontexte = new modele_vivo_amoreContainer())
    {
        try
        {
            if (e.Item.ItemType == ListViewItemType.DataItem)
            {
                Membre membrealecran = (Membre)e.Item.DataItem;
                Membre lemembre = (lecontexte.Set<Membre>().Find(membrealecran.Pseudo));
            }
        }
        catch (Exception ex)
        {
            lblMessage.Text += "ERREUR DE ITEMDATABOUND, " + ex.ToString();
        }
    }

Answer 1

.Find are seaching for entity by primary key. You need to pass primary key as parameter. Use SingleOrDefault for seaching by non primary key param:

...
Membre lemembre = lecontexte.Set<Membre>().SingleOrDefault(m => m.Pseudo == membrealecran.Pseudo);