title: How do I bind a DataGridComboBoxColumn to EntityFramework using MVVM?
body: <p>I'm trying to get a DataGridComboBoxColumn working with my ViewModel. Everything appears to work correctly but when I change the value of the combo box, the entity isn't changed. </p>
  
  <p>The datacontext of the window has these properties:</p>
  
  <p><strong>ItemsSource</strong></p>
  
  <pre><code>Public Property AllEnergySources() As ObservableCollection(Of EnergySourceViewModel)
  </code></pre>
  
  <p><strong>SelectedItemBinding</strong></p>
  
  <pre><code>  Private _CurrentEnergySource As EnergySourceViewModel
      Public Property CurrentEnergySource() As EnergySourceViewModel
          Get
              Return _CurrentEnergySource
          End Get
          Set(ByVal value As EnergySourceViewModel)
              _CurrentEnergySource = value
              OnPropertyChanged("CurrentEnergySource")
          End Set
      End Property
  </code></pre>
  
  <p>I feel the problem lies with how I populate CurrentEnergySource in the ViewModel that is the DataContext:</p>
  
  <pre><code>Sub New(SelectedEntity as EquipmentEnergySource)
       AllEnergySources = New ObservableCollection(Of EnergySourceViewModel)
  
      //Select all EnergySources from the EntityFramework
       Dim EnergyEntities = From esr in db.EnergySources Select esr
  
                  //Loop through to convert Entity POCO to Collection of ViewModels
                  For Each es In EnergyEntities
                      _AllEnergySources.Add(New EnergySourceViewModel(es))
  
                      //Optionally Set the newly created ViewModel to SelectedItemBinding object
                      If es.EnergySourceID = SelectedEntity.EnergySourceID Then
                          _CurrentEnergySource = _AllEnergySources.Last
                      End If
                  Next
  End Sub
  </code></pre>
  
  <p>When I create the backing collection for the combobox, if the model is the selected one, I set that viewmodel to be the CurrentEnergySource but after that point it is disconnected(and that's the problem)</p>
  
  <p>What should I reference in CurrentEnergySource so that it updates the model when the combo box changes?</p>