LINQ query to flatten master/detail with sub-details

Question

I have the following classes:

public class Order
{
    public Order()
    {
        Items = new ObservableCollection<OrderItem>();
    }

    public string Code { get; set; }
    public ICollection<OrderItem> Items { get; set; }
}

public class OrderItem
{
    public OrderItem()
    {
        SubItems = new ObservableCollection<SubItem>();
    }

    public decimal Quantity { get; set; }
    public decimal Price { get; set; }
    public ICollection<SubItem> SubItems { get; set; }        
}

public class SubItem
{
    public DateTime Date { get; set; }
    public decimal Quantity { get; set; }
    public string UserName { get; set; }
}

Now the problem I have is that I want to show all the data on those classes in a datagrid, eg. using the code:

Order order = new Order();
        order.Code = "123";
        order.Items.Add(new OrderItem()
                                {
                                    Price = 30,
                                    Quantity = 3,
                                    SubItems = new Collection<SubItem>()
                                        {
                                            new SubItem() { Date = DateTime.Now, Quantity = 1, UserName = "User1" }, 
                                            new SubItem() { Date = DateTime.Now, Quantity = 2, UserName = "User2" }
                                        }
                                });


        order.Items.Add(new OrderItem()
                                {
                                    Price = 500,
                                    Quantity = 50,
                                    SubItems = new Collection<SubItem>()
                                        {
                                            new SubItem() { Date = DateTime.Now, Quantity = 20, UserName = "User1" }, 
                                            new SubItem() { Date = DateTime.Now, Quantity = 20, UserName = "User2" },
                                            new SubItem() { Date = DateTime.Now, Quantity = 10, UserName = "User3" }
                                        }
                                });

I need to show on a DataGrid something like this:

| Order.Code | Item.Price | Item.Quantity | SubItem.Quantity | SubItem.UserName |
| 123        | 30         | 3             | 1                |  User1           |
| 123        | 30         | 3             | 2                |  User2           |
| 123        | 500        | 50            | 20               |  User1           |
| 123        | 500        | 50            | 20               |  User2           |
| 123        | 500        | 50            | 10               |  User3           |

Looks simple enough but I just can't do it. The best I could do is to put a reference to OrderItem on SubItem so I can use it on the column databind but that only works when I have subItems (and if there is not SubItems, I still need to show the OrderItem data). So basically I need to show the exact thing I see if I execute a SQL SELECT joining the 3 tables.

Any linq magic can do this?

Answer 1

Try this, it's like a join:

var table = from item in order.Items
            from subItem in item.SubItems
            select new
                {
                    OrderCode = order.Code,
                    ItemPrice = item.Price,
                    ItemQuantity = item.Quantity,
                    SubItemQuantity = subItem.Quantity,
                    SubItemUserName = subItem.UserName
                };

You can extend this to multiple orders if you like:

var table = from order in orders
            from item in order.Items
            from subItem in item.SubItems
            select new
                {
                    OrderCode = order.Code,
                    ItemPrice = item.Price,
                    ItemQuantity = item.Quantity,
                    SubItemQuantity = subItem.Quantity,
                    SubItemUserName = subItem.UserName
                };

And here's a link: http://msdn.microsoft.com/en-us/library/bb383978.aspx (see Compound from Clause)

If the collections can be empty, use DefaultIfEmpty(), e.g.:

var table = from order in orders
            from item in order.Items.DefaultIfEmpty(new OrderItem())
            from subItem in item.SubItems.DefaultIfEmpty(new SubItem())
            select new
                {
                    OrderCode = order.Code,
                    ItemPrice = item.Price,
                    ItemQuantity = item.Quantity,
                    SubItemQuantity = subItem.Quantity,
                    SubItemUserName = subItem.UserName
                };

If you don't pass in an argument to DefaultIfEmpty() the "default" item will be null, so you'll have to deal with that, e.g.:

var table = from order in orders
            from item in order.Items.DefaultIfEmpty()
            from subItem in (item != null ? item.SubItems : Enumerable.Empty<SubItem>()).DefaultIfEmpty()
            select new
                {
                    OrderCode = order.Code,
                    ItemPrice = item != null ? item.Price.ToString() : "n/a",
                    ItemQuantity = item != null ? item.Quantity.ToString() : "n/a",
                    SubItemQuantity = subItem != null ? subItem.Quantity.ToString() : "n/a",
                    SubItemUserName = subItem != null ? subItem.UserName : "n/a"
                };

Another alternative:

var table = from order in orders
            from item in order.Items.DefaultIfEmpty()
            from subItem in (item != null ? item.SubItems : Enumerable.Empty<SubItem>()).DefaultIfEmpty()
            select new
                {
                    OrderCode = order.Code,
                    ItemPrice = item != null ? item.Price : default(decimal?),
                    ItemQuantity = item != null ? item.Quantity : default(decimal?),
                    SubItemQuantity = subItem != null ? subItem.Quantity : default(decimal?),
                    SubItemUserName = subItem != null ? subItem.UserName : null
                };

Answer 2

Flattening using the SelectMany method:

var res = order.Items
               .SelectMany(i => i.SubItems, (Item, Sub) => new { Item, Sub })
               .Select(r => new { order.Code, 
                                  r.Item.Price, 
                                  ItemQuantity = r.Item.Quantity, 
                                  SubItemQuantity = r.Sub.Quantity, 
                                  r.Sub.UserName });

If the SubItems collection could be empty, you can use DefaultIfEmpty method:

var res = order.Items
               .SelectMany(i => i.SubItems.DefaultIfEmpty(), (Item, Sub) => new { Item, Sub })
               .Select(r => new { order.Code, 
                                  r.Item.Price, 
                                  ItemQuantity = r.Item.Quantity, 
                                  SubItemQuantity = r.Sub == null ? null : (Decimal?) r.Sub.Quantity ,
                                  UserName = r.Sub == null ? (string)null : r.Sub.UserName });

Try on Ideone.