New Post: EF5 + How to save an entity with its child entities at the same time to the database?

EF5 + How to save an entity with its child entities at the same time to the database?

3 minutes ago|LINK

I have two entities in my project (actually three with the item entity).

public class Purchase
{
    [Key]
    public string TrNo { get; set; }
    [Required]
    public DateTime Date { get; set; }
    [Required]
    public int SupplierID { get; set; }

    public ObservableCollection<PurchaseDetail> PurchaseDetails { get; set; }
}

and

public class PurchaseDetail
{
    [Key, Column(Order = 0)]
    public string TrNo { get; set; }
    [Key, Column(Order = 1)]
    public int ItemID { get; set; }
    [Required]
    public double Qty { get; set; }
    [Required]
    public decimal CostPrice { get; set; }
    [Required]
    public decimal TotalCost { get; set; }

    public virtual Purchase Purchases { get; set; }
    public virtual Item Items { get; set; }
}

In the Purchase form, when user adding item s to a grid, I'm creating an

ObservableCollection<PurchaseDetail> PurchaseDetails with added items.

And, finally a Purchase entity.

When the user clicks on the Save button, I want to save the item details (purchased) into the PurchaseDetails table and main data into the Purchases table.

Please help me to do this job in a right (standard) way.