Entity Framework Linq - how to get groups that contain all your data - linq

Question

Here a sample dataset:
OrderProduct is a table that contains the productIds that were part of a given order.
Note: OrderProduct is a database table and I am using EF.
OrderId, ProductId
1, 1
2, 2
3, 4
3, 5
4, 5
4, 2
5, 2
5, 3
What I want to be able to do is find an order that contains only the productIds that I am searching for. So if my input was productIds 2,3, then I should get back OrderId 5.
I know how I can group data, but I am unsure of how to perform the select on the group.
Here is what I have:
var q = from op in OrderProduct
group op by op.OrderId into orderGroup
select orderGroup;
Not sure how to proceed from here

Answer 1

IEnumerable<int> products = new List<int> {2, 3};
IEnumerable<OrderProduct> orderProducts = new List<OrderProduct>
{
new OrderProduct(1, 1),
new OrderProduct(2, 2),
new OrderProduct(3, 4),
new OrderProduct(3, 5),
new OrderProduct(4, 5),
new OrderProduct(4, 2),
new OrderProduct(5, 2),
new OrderProduct(5, 3),
};
var orders =
(from op in orderProducts
group op by op.OrderId into orderGroup
//magic goes there
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
select orderGroup);
//outputs 5
orders.Select(x => x.Key).ToList().ForEach(Console.WriteLine);
Or you can have another version as pointed in another answer, just replace
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
on
where products.All(pid => orderGroup.Any(op => op.ProductId == pid))
second one will have ~ 15% better performance (I've checked that)
Edit
According to the last requirement change, that you need orders that contain not all productIds you are searching, but exactly those and only those productIds, I wrote an updated version:
var orders =
(from op in orderProducts
group op by op.OrderId into orderGroup
//this line was added
where orderGroup.Count() == products.Count()
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
select orderGroup);
So the only thing you'll need is to add a precondition ensuring that collections contains the same amount of elements, it will work for both previous queries, and as a bonus I suggest 3rd version of the most important where condition:
where orderGroup.Select(x => x.ProductId).Intersect(products).Count() == orderGroup.Count()

Answer 2

At first glance, I'd try something like this:
var prodIds = new[] {2, 3};
from o in context.Orders
where prodIds.All(pid => o.OrderProducts.Any(op => op.ProductId == pid))
select o
In plain language: "get the orders that have a product with every ID in the given list."
Update
Since it appears you are using LINQ to SQL rather than LINQ to Entities, here's another approach:
var q = context.Orders;
foreach(var pid in prodIds)
{
q = q.Where(o => o.OrderProducts.Any(op => op.ProductId == pid));
}
Rather than using a single LINQ statement, you essentially build the query piecemeal.

Answer 3

Thanks to StriplingWarrior's answer I managed to figure this out. Not sure if this is the best way to do this, but it works.
List<int> prodIds = new List<int>{2,3};
var q = from o in Orders
//get all orderproducts that contain products in the ProdId list
where o.OrderProducts.All(op => prodIds.Contains(op.ProductId))
//now group the OrderProducts by the Orders
select from op in o.OrderProducts
group op by op.OrderId into opGroup
//select only those groups that have the same count as the prodId list
where opGroup.Count() == prodIds.Count()
select opGroup;
//get rid of any groups that may be empty
q = q.Where(fi => fi.Count()> 0);
(I am using LinqPad, which is why the query looks a little funky - no context, etc)