How to save ObservableCollection to EntityFramework Model string using MultiSelectComboBox

Hi Guys,

Within my application, I have a ComboBox that a user could select multiple items from thatComboBox.

So far, I have been following this link and it is exactly the sort of thing that I needed. 

After implementing it, I have came across a few issues. Firstly, within my ViewModel, I assign my properties to the data entities within my Entity Framework model within my constructor like so;

 public EmployeeViewModel(DataObjects.Employee e)
            : base("")
        {
            Title = e.Title;
            FirstName = e.FirstName;
            Surname = e.Surname;
        }

But When I try to assign the values from the example site it produces this error;

Benefits = e.BenefitsProvided;

private ObservableCollection<string> _benefits = new ObservableCollection<string> {"Items"};

public ObservableCollection<string> Benefits
        {
            get { return _benefits; }
        }
        private string _selectedBenefit = "None";
        public string SelectedBenefit
        {
            get { return _selectedBenefit; }
            set
            {
                    _selectedBenefit = value;
                    OnPropertyChanged("SelectedBenefit");
            }
        }
        private ObservableCollection<string> _selectedBenefits;   
        public ObservableCollection<string> SelectedBenefits
        {
            get
            {
                if (_selectedBenefits == null)
                {
                    _selectedBenefits = new ObservableCollection<string> {"None"};
                    SelectedBenefitsText = WriteSelectedBenefitsString(_selectedBenefits);
                    _selectedBenefits.CollectionChanged +=
                        (s, e) =>
                        {
                            SelectedBenefitsText = WriteSelectedBenefitsString(_selectedBenefits);
                            OnPropertyChanged("SelectedBenefits");
                        };
                    }
                return _selectedBenefits;
            }
            set
            {
                _selectedBenefits = value;
            }
        }

        public string SelectedBenefitsText
        {
            get { return _SelectedBenefitsText; }
            set
            {
                _SelectedBenefitsText = value;
                
                OnPropertyChanged("SelectedBenefitsText"); 
            }
        }
        string _SelectedBenefitsText;
        private static string WriteSelectedBenefitsString(IList<string> list)
        {
            if (list.Count == 0)
            
                return String.Empty;
            
            StringBuilder builder = new StringBuilder(list[0]);

            for (int i = 1; i < list.Count; i++)
            {
                builder.Append(", ");
                builder.Append(list[i]);
            }
                return builder.ToString();
        }

Error	2	Cannot implicitly convert type 'string' to 'System.Collections.ObjectModel.ObservableCollection<string>'

This is how I bind this to my xaml;

<src:MultiComboBox Grid.Column="1" Grid.Row="9"
                             SelectionMode="Multiple" 
                             VerticalAlignment="Center"
                             DisplaySeparator=", "
                             ItemsSource="{Binding Benefits}"
                             SelectedItems="{Binding SelectedBenefits}"></src:MultiComboBox>

I understand that you can not assign a property of ObservableCollection<string>to a string. Which leads me to my question, is there some sort of converter or a way of saving a collection to an entity field within my EntityFramework model. (BenefitsProvided is a nvarchar within EF)

Many thanks,

Greg.