WPF中的MVVM和Entity Framework未处理的异常

Question

This is driving me mad. I'm fairly new to WPF/EF.

I have a simple MVVM app which reads an Entity Table into a DataGrid via binding in the XAML. The app compiles fine.

I am getting this unhandled exception however which locks the designer:

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)

The XAML cannot create an instance of my View Model...

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

Here is my View Model 'Load Grid' method:

 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!"));
            }
        }

The connection string in my App.config was created on creation of my EF model and populates the DataGrid as intended.

Any ideas what is causing this?

Friday afternoon frustration! Thanks

Edit: 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

When you add your ERM to the project it will create models for you.

If you have a table in your db called tblYears for example you should be able to declare:

tblYear y = new tblYear();

I personally create a local model and populate it to use in the view ie 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
}

You can then use this view model to either populate a List<> or as an individual record - list example:

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
}

Then for example you can send it to a page like so:

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

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

And bind it to a control:

<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>

Hope this helps GL