Q:

How to display List<> items in a DataGrid cell? 

I have a DataGrid with autogenerated columns.  The ItemsSource is a result of LINQ to Entity query to a EF context.  One of the columns contains lists of entities.  How can I make it show the names of the entities instances? 
The function loading the DataGrid:
    private void DataGridRecipientsLoad()
    {
        List<Recipient> recipients = _recipientService. GetAllRecipients();
        dataGridRecipients. ItemsSource = from rec in recipients select rec;
        if (recipients. Count() == 0) return;
        dataGridRecipients. Columns[7].Visibility = System. Windows. Visibility. Collapsed;
        dataGridRecipients. Columns[8].Visibility = System. Windows. Visibility. Collapsed;
    }

The Recipient definition:
[EdmEntityTypeAttribute(NamespaceName="NewsletterModel", Name="Recipient")]
    [Serializable()]
    [DataContractAttribute(IsReference=true)]
    public partial class Recipient : EntityObject
    {
    #region Factory Method

    /// <summary>
    /// Create a new Recipient object. 
    /// </summary>
    /// <param name="recipientID">Initial value of the RecipientID property.</param>
    /// <param name="firstName">Initial value of the FirstName property.</param>
    /// <param name="email">Initial value of the Email property.</param>
    public static Recipient CreateRecipient(global::System. Int32 recipientID, global::System. String firstName, global::System. String email)
    {
        Recipient recipient = new Recipient();
        recipient. RecipientID = recipientID;
        recipient. FirstName = firstName;
        recipient. Email = email;
        return recipient;
    }

    #endregion

    #region Primitive Properties

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=true, IsNullable=false)]
    [DataMemberAttribute()]
    public global::System. Int32 RecipientID
    {
        get
        {
            return _RecipientID;
        }
        set
        {
            if (_RecipientID ! = value)
            {
                OnRecipientIDChanging(value);
                ReportPropertyChanging("RecipientID");
                _RecipientID = StructuralObject. SetValidValue(value);
                ReportPropertyChanged("RecipientID");
                OnRecipientIDChanged();
            }
        }
    }
    private global::System. Int32 _RecipientID;
    partial void OnRecipientIDChanging(global::System. Int32 value);
    partial void OnRecipientIDChanged();

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=false)]
    [DataMemberAttribute()]
    public global::System. String FirstName
    {
        get
        {
            return _FirstName;
        }
        set
        {
            OnFirstNameChanging(value);
            ReportPropertyChanging("FirstName");
            _FirstName = StructuralObject. SetValidValue(value, false);
            ReportPropertyChanged("FirstName");
            OnFirstNameChanged();
        }
    }
    private global::System. String _FirstName;
    partial void OnFirstNameChanging(global::System. String value);
    partial void OnFirstNameChanged();

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=true)]
    [DataMemberAttribute()]
    public global::System. String LastName
    {
        get
        {
            return _LastName;
        }
        set
        {
            OnLastNameChanging(value);
            ReportPropertyChanging("LastName");
            _LastName = StructuralObject. SetValidValue(value, true);
            ReportPropertyChanged("LastName");
            OnLastNameChanged();
        }
    }
    private global::System. String _LastName;
    partial void OnLastNameChanging(global::System. String value);
    partial void OnLastNameChanged();

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=true)]
    [DataMemberAttribute()]
    public global::System. String City
    {
        get
        {
            return _City;
        }
        set
        {
            OnCityChanging(value);
            ReportPropertyChanging("City");
            _City = StructuralObject. SetValidValue(value, true);
            ReportPropertyChanged("City");
            OnCityChanged();
        }
    }
    private global::System. String _City;
    partial void OnCityChanging(global::System. String value);
    partial void OnCityChanged();

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=false)]
    [DataMemberAttribute()]
    public global::System. String Email
    {
        get
        {
            return _Email;
        }
        set
        {
            OnEmailChanging(value);
            ReportPropertyChanging("Email");
            _Email = StructuralObject. SetValidValue(value, false);
            ReportPropertyChanged("Email");
            OnEmailChanged();
        }
    }
    private global::System. String _Email;
    partial void OnEmailChanging(global::System. String value);
    partial void OnEmailChanged();

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [EdmScalarPropertyAttribute(EntityKeyProperty=false, IsNullable=true)]
    [DataMemberAttribute()]
    public global::System. String Phone
    {
        get
        {
            return _Phone;
        }
        set
        {
            OnPhoneChanging(value);
            ReportPropertyChanging("Phone");
            _Phone = StructuralObject. SetValidValue(value, true);
            ReportPropertyChanged("Phone");
            OnPhoneChanged();
        }
    }
    private global::System. String _Phone;
    partial void OnPhoneChanging(global::System. String value);
    partial void OnPhoneChanged();

    #endregion

    #region Navigation Properties

    /// <summary>
    /// No Metadata Documentation available. 
    /// </summary>
    [XmlIgnoreAttribute()]
    [SoapIgnoreAttribute()]
    [DataMemberAttribute()]
    [EdmRelationshipNavigationPropertyAttribute("NewsletterModel", "RecipientMailingList", "MailingList")]
    public EntityCollection<MailingList> MailingList
    {
        get
        {
            return ((IEntityWithRelationships)this).RelationshipManager. GetRelatedCollection<MailingList>("NewsletterModel. RecipientMailingList", "MailingList");
        }
        set
        {
            if ((value ! = null))
            {
                ((IEntityWithRelationships)this).RelationshipManager. InitializeRelatedCollection<MailingList>("NewsletterModel. RecipientMailingList", "MailingList", value);
            }
        }
    }

    #endregion

}

I want to display all MailingLists that each Recipient belongs to. 

A:

Create a ViewModel that has your Recipient object.  
Create a property for the Recipient object that implements INotifyPropertyChanged. 
Add another property for your MailingList.  Have the Recipient property also notify property changed for your MailingList. 
public Recipient Recipient
{
    get { return _Recipient; }
    set
    {
        _Recipient = value;
        NotifyPropertyChanged("Recipient");
        NotifyPropertyChanged("MailingList");
    }
} private Recipient _Recipient

public EntityCollection<MailingList> MailingList
{
    get { return _MailingList; }
    set
    {
        _MailingList= value;
        NotifyPropertyChanged("MailingList");
    }
} private EntityCollection<MailingList> _MailingList

Then in your View, I assume you have some way to select the person or recipient and when you select them, the Recipient would change.  Then another view should exist to show the mailing list.  Then bind your DataGrid's ItemsSource to the MailingList property.  
I assume EntityCollection is an IList or IEnumerable, otherwise, you may have to convert it to something like a List or ObservableCollection.  If you need to, create a MailingListViewModel and create your List or ObservableCollection if you have to. 
Also, I am assuming that the MailingList has a property for the name that the auto generate columns can use, otherwise you need to build your columns and not auto generate them.