用实体框架实现MVVM模式-添加-删除

我正试图在我的WPF项目上实现MVVM模式，该项目使用实体框架来获取/操作数据。我很困惑，我想知道在数据库中验证模型对象集合的更改应该在哪里？？？我的应用程序如下：在我的视图中，我有一个人员数据网格，两个文本框将加载所选人员的姓名，一个用于更新行更改的按钮和一个用于删除所选行的按钮。

在我的ModelView中，我有一个observableCollection，它将在类初始化时加载，其中包含来自我的数据库（实体）的信息+两个用于添加/删除按钮的Relaycommands（请找到下面的代码）。

问题是我没有很好地理解MVVM的原理，在哪里、何时以及如何将对我的数据的修改推送到数据库？目前，当我更新数据库中的一行，并保存我对可观察集合的DB上下文修改时，提交了，但当我删除一个项时，它不是cdase，我必须在数据库中手动查找它并删除它（我已将我的可观察集合附加到将处理此问题的NotifyCollectionChangedEventHandler事件）。。。我不明白使用Observable集合的意义！！！

对于使用数据库数据的"完美"mvvm体系结构，有什么简单的解释吗？？？谢谢我的ViewModel

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections.ObjectModel;
using System.Windows.Data;
using System.ComponentModel;
using System.Windows.Input;
using System.Windows;
using MVVMOK.Models;
using MVVMOK.Base;
using System.Collections.Specialized;
namespace MVVMOK.ViewModel
{
    class MainWindowViewModel : ViewModelBase
    {
        private DW_MargoEntities contexte;

        //Constructor
        public MainWindowViewModel()
        {
            contexte = new DATABASEEntities();
            collectionOfCollaborators = new ObservableCollection<Collaborator>();
            foreach (Collaborator c in contexte.Collaborator)
            {
                collectionOfCollaborators.Add(c);
            }

            //Abonnement pour l'ajout ou la suppression d'éléments :
            collectionOfCollaborators.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(collectionOfCollaboratorsChanged);
            //Assignation des commandes : 
            this._deleteComand = new RelayCommand(new Action<object>(DeleteRow));
            this._updateCommand = new RelayCommand(new Action<object>(UpdateDB));
        }
        //liste des propriétés publiques:

        //Propriété pour représenter l'élément séléctionné du datagrid
        private  Collaborator selectedItem;
        public Collaborator _selectedItem
        {
            get { return selectedItem; }
            set
            {
                if (value != selectedItem)
                {
                    selectedItem = value;
                    OnPropertyChanged("_selectedItem");
                };
            }
        }
        //Propriété pour représenter l'élément séléctionné:
        private ObservableCollection<Collaborator> collectionOfCollaborators;
        public ObservableCollection<Collaborator> _collectionOfCollaborators
        {
            get { return collectionOfCollaborators; }
            set
            {
                this.collectionOfCollaborators = value;
                OnPropertyChanged("_collectionOfCollaborators");
            }
        }
        //Commandes : 
        public ICommand _updateCommand
        {
            get;
            set;
        }
        public ICommand _deleteComand
        {
            get;
            set;
        }
        void collectionOfCollaboratorsChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            Collaborator f = new Collaborator();
            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    for(int i = 0; i<e.NewItems.Count;i++)
                    {
                        if (e.NewItems[i].GetType().Equals(f.GetType()))
                        {
                            contexte.Collaborator.Add(e.NewItems[i] as Collaborator);
                        }
                    }
                    contexte.SaveChanges();
                    break;
                case NotifyCollectionChangedAction.Remove:
                    for (int i = 0; i < e.OldItems.Count; i++)
                    {
                        if (e.OldItems[i].GetType().Equals(f.GetType()))
                        {
                            contexte.Collaborator.Remove(e.OldItems[i] as Collaborator);
                        }
                    }
                    contexte.SaveChanges();
                    break;
                //Reset = Clear
            }
        }

        //Services :
        public void UpdateDB(object msg)
        {
            contexte.SaveChanges();
        }

        public void DeleteRow(object msg)
        {
            _collectionOfCollaborators.Remove(_selectedItem);
            contexte.SaveChanges();
        }
    }
}

我的型号

namespace MVVMOK.Models
{
    using System;
    using System.Collections.Generic;
    public partial class Collaborator
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Surname { get; set; }
    }
}

我的XAML

<Window x:Class="MVVMOK.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:local="clr-namespace:MVVMOK.ViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <!-- Declaratively create an instance of our SongViewModel -->
        <local:MainWindowViewModel />
    </Window.DataContext>
    <Grid>
        <Grid Height="237" HorizontalAlignment="Left" Margin="12,12,0,0" Name="grid1" VerticalAlignment="Top" Width="479">
            <DataGrid AutoGenerateColumns="False" Height="237" HorizontalAlignment="Left" Name="dataGrid1" VerticalAlignment="Top" Width="479" ItemsSource="{Binding Path=_collectionOfCollaborators, Mode=TwoWay}" SelectionMode="Single" SelectedItem="{Binding Path=_selectedItem, Mode=TwoWay}"  >
                <DataGrid.Columns>
                    <DataGridTextColumn Binding="{Binding Path=Id}" Header="ID" />
                    <DataGridTextColumn Binding="{Binding Path=Name}" Header="Name" Width="4*" />
                </DataGrid.Columns>
            </DataGrid>
        </Grid>
        <TextBox Height="23" HorizontalAlignment="Left" Margin="104,255,0,0" Name="textBox1" VerticalAlignment="Top" Width="120" Text ="{Binding Path=_selectedItem.Name, Mode=TwoWay}" />
        <TextBox Height="23" HorizontalAlignment="Left" Margin="104,283,0,0" Name="textBox2" VerticalAlignment="Top" Width="120" Text ="{Binding Path=_selectedItem.Surname, Mode=TwoWay}" />
        <Label Content="Name" Height="28" HorizontalAlignment="Left" Margin="50,255,0,0" Name="label1" VerticalAlignment="Top" />
        <Label Content="Surname" Height="28" HorizontalAlignment="Left" Margin="37,283,0,0" Name="label2" VerticalAlignment="Top" />
        <Button Content="Delete Row" Height="23" HorizontalAlignment="Left" Margin="416,260,0,0" Name="button1" VerticalAlignment="Top" Width="75" Command="{Binding Path=_deleteComand}"/>
        <Button Content="Update All" Height="23" HorizontalAlignment="Left" Margin="335,260,0,0" Name="button2" VerticalAlignment="Top" Width="75" Command="{Binding Path=_updateCommand}"/>
    </Grid>
</Window>