public <userdata> userdata { get; set; }

 [Include]
 EntityCollection<userdata> userdata { get; set; }

public IQueryable<user> Getuser()
        {
            //return this.ObjectContext.user;
            return this.ObjectContext.user.Include("userdata").OrderBy(e => e.login);
        }

       <sdk:DataGrid AutoGenerateColumns="True" HorizontalAlignment="Stretch"  Name="dataGrid1" VerticalAlignment="Stretch" ItemsSource="{Binding ElementName=userDomainDataSource, Path=Data}">
            <sdk:DataGrid.Columns>
                <sdk:DataGridCheckBoxColumn 
                    Binding="{Binding Path=userdata.fio}" 
                    Header="ФИО" Width="Auto" />
                </sdk:DataGrid.Columns>
         </sdk:DataGrid>

public <userdata> userdata { get; set; }

 [Include]
 EntityCollection<userdata> userdata { get; set; }

[Include]
public <userdata> userdata { get; set; }