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Sublist X LINQ

Posted on 2009-07-10
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Last Modified: 2013-11-11
hello,

I have a class

class Invoice
{
   int id;
   DateTime date;
  List<InvoiceItem> items;
}

class InvoiceItem
{
   Invoice invoice;
   int qty;
   decimal value;
}

if I have
List<Invoice> invoices;
that has a list of my invoices read from DB and their respective invoice items, using LINQ, how to I get a list of invoices and invoice items that has qty > 2?

I tried, without success:
var res =
  from invoice from invoices
 join items in invoice.items on invoices.id equals items.invoice.id
where items.qty > 2
select new { invoice.date, items.value };
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Comment
Question by:jeovaalmeida
  • 2
3 Comments
 
LVL 63

Accepted Solution

by:
Fernando Soto earned 250 total points
ID: 24827762
Hi jeovaalmeida;

The code snippet below should give you what you want.

Fernando
var results = from invoice in invoices
              from item in invoice.items
              where item.qty > 2
              select new { invoice.date, item.value };
 
foreach (var invoice in results)
{
    Console.WriteLine("{0,-24}{1}", invoice.date, invoice.value);
}

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0
 

Author Comment

by:jeovaalmeida
ID: 24839275
hello fernando,

thanks for your help. it worked, but ...

why the code didn't return a cartesian result?
the where clause (where item.qty > 2) only filtered qtd > 2.

if I use (where item.qty > 2 && item.invoice.id == invoice.id) (that is, joining the two collections), the result is the same.

is that because invoice.items is a subitem of invoice that the join isn't needed?
0
 
LVL 63

Expert Comment

by:Fernando Soto
ID: 24839624
Hi jeovaalmeida;

Question:
why the code didn't return a cartesian result?
the where clause (where item.qty > 2) only filtered qtd > 2.

Answer:
It does not return a cartesian product because the query is not doing a join on the class Invoice but is getting the InvoiceItem from the member property of Invoice class which seems to hold the InvoiceItem for each invoice.

Question:
if I use (where item.qty > 2 && item.invoice.id == invoice.id) (that is, joining the two collections), the result is the same.

Answer:
That is NOT joining the two collections. It is ferther filtering the result based on two items in stead of one.

Question:
is that because invoice.items is a subitem of invoice that the join isn't needed?

Answer:
Yes, a join is not needed in this case because InvoiceItem is a collection within the Invoice class.

Fernando
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