WPF中的MVVM和Entity Framework未處理的異常

Question

這讓我發瘋。 我是WPF / EF的新手。

我有一個簡單的MVVM應用程序，該應用程序通過XAML中的綁定將實體表讀入DataGrid。 該應用程序編譯正常。

我遇到了這個未處理的異常，但是它鎖定了設計器：

The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid.
at System.Data.EntityClient.EntityConnection.ChangeConnectionString(String newConnectionString)
at System.Data.EntityClient.EntityConnection..ctor(String connectionString)
at System.Data.Objects.ObjectContext.CreateEntityConnection(String connectionString)

XAML無法創建我的視圖模型的實例...

xmlns:vm="clr-namespace:Entity_MVVM"
    Title="MainWindow" Height="600" Width="800"
    DataContext="{DynamicResource MyViewModel}">
<Window.Resources>
    <vm:CountrysViewModel x:Key="MyViewModel"/>
</Window.Resources>

這是我的視圖模型“加載網格”方法：

 public void LoadGrid()

    {
        var db = new LDBEntities();
        using (var conn = new EntityConnection("name=LDBEntities"))
        {
            conn.Open();
            EntityCommand cmd = conn.CreateCommand();
            cmd.CommandText = "SELECT VALUE c FROM LDBEntities.tbCountrys as c";

            try
            {
                EntityDataReader rdr = cmd.ExecuteReader(CommandBehavior.SequentialAccess | CommandBehavior.CloseConnection);

                _CountrysModelObservableList.Clear();

                while (rdr.Read())
                {
                    var cCountryId = rdr["CountryId"].ToString();
                    var cShortName = rdr["shortName"].ToString();
                    var cLongName = rdr["longName"].ToString();

                    _CountrysModelView = new CountrysModel()
                    {
                        CountryId = cCountryId,
                        ShortName = cShortName,
                        LongName = cLongName
                    };

                    _CountrysModelObservableList.Add(_CountrysModelView);
                }
            }
            catch(Exception e)
            {
                MessageBox.Show(string.Format("Can't read in data!"));
            }
        }

App.config中的連接字符串是在創建EF模型時創建的，並按預期填充了DataGrid。

任何想法是什么原因造成的？

星期五下午無奈！ 謝謝

編輯：App.Config：

<?xml version="1.0" encoding="utf-8"?>
<configuration>
<connectionStrings>
<add name="LDBEntities" connectionString="metadata=res://*/DataModel.csdl|res://*/DataModel.ssdl|res://*/DataModel.msl;provider=System.Data.SqlClient;provider connection string='Data Source=DMEA-T1000\SQLEXPRESS;Initial Catalog=LDB;Persist Security Info=True;User ID=sa;Password=PasswordHidden;MultipleActiveResultSets=True' " providerName="System.Data.EntityClient" /></connectionStrings>
</configuration>

Answer 1

將ERM添加到項目時，它將為您創建模型。

例如，如果數據庫中有一個名為tblYears的表，則應該可以聲明：

tblYear y = new tblYear();

我個人創建了一個本地模型，並將其填充到視圖中使用，即viewmodel。

class YearModel : INotifyPropertyChanged
{

#region Members

    MyERM.tblYear _year;

#endregion

#region Properties

    public MyERM.tblYear Year
    {
        get { return _year; }
    }

    public Int32 id
    {
        get { return Year.id; }
        set
        {
            Year.id = value;
            NotifyPropertyChanged("id");
        }
    }

    public String Description
    {
        get { return Year.Description; }
        set
        {
            Year.Description = value;
            NotifyPropertyChanged("Description");
        }
    }

#endregion

#region Construction

    public YearModel()
    {
        this._year = new MyERM.Year
        {
            id = 0,
            Description = ""
        };
    }

#endregion
}

然后，您可以使用此視圖模型填充List <>或作為單個記錄-列表示例：

class YearListModel
{
    myERM db = new myERM();

    #region Members

    private ObservableCollection<YearModel> _years;

    #endregion

    #region Properties

    public ObservableCollection<YearModel> Years
    {
        get { return _years; }
    }

    #endregion

    #region Construction

    public YearListModel()
    {
        _years = new ObservableCollection<YearModel>();

        foreach (MyERM.tblYear y in db.tblYears())
        {
            _years.Add(new YearModel
            {
                id = y.id,
                Description = y.Description
            }
          );
        }
    }

    #endregion
}

然后，例如，您可以將其發送到如下頁面：

xmlns:local="clr-namespace:MyProject.ViewModels"

<Page.Resources>
    <local:YearListModel x:Key="YearList" />
</Page.Resources>

並將其綁定到控件：

<ListView x:Name="listviewname"
          DataContext="{StaticResource ResourceKey=YearList}"
          ItemsSource="{Binding Path=Years}">
    <ListView.View>
        <GridView>
            <GridViewColumn x:Name="columnname" Header="Code" 
                            DisplayMemberBinding="{Binding Code}"/>
        </GridView>
    </ListView.View>
</ListView>

希望這對GL有幫助