I have a list of orders.
I want to select orders based on a set of order statuses.
So essentially select orders where order.StatusCode in ("A", "B", "C")
// Filter the orders based on the order status
var filteredOrders = from order in orders.Order
where order.StatusCode.????????("A", "B", "C")
select order;
Your status-codes are also a collection, so use Contains:
var allowedStatus = new[]{ "A", "B", "C" };
var filteredOrders = orders.Order.Where(o => allowedStatus.Contains(o.StatusCode));
or in query syntax:
var filteredOrders = from order in orders.Order
where allowedStatus.Contains(order.StatusCode)
select order;
HashSet<T> in the first place. But it's not a good idea always: You need another collection, so more memory, if you pass in already an array or list. You need to fill that HashSet<T>, so more cpu cycles. You might not be able to use thousands of items anyway if this is not Linq-To-Objects but Linq-To-Entities(the Contains is translated to an sql-IN clause which has limitations).
NB: this is LINQ to objects, I am not 100% sure if it works in LINQ to entities, and have no time to check it right now. In fact it isn't too difficult to translate it to x in [A, B, C] but you have to check for yourself.
So, instead of Contains as a replacement of the ???? in your code you can use Any which is more LINQ-uish:
// Filter the orders based on the order status
var filteredOrders = from order in orders.Order
where new[] { "A", "B", "C" }.Any(s => s == order.StatusCode)
select order;
It's the opposite to what you know from SQL this is why it is not so obvious.
Of course, if you prefer fluent syntax here it is:
var filteredOrders = orders.Order.Where(order => new[] {"A", "B", "C"}.Any(s => s == order.StatusCode));
Here we again see one of the LINQ surprises (like Joda-speech which puts select at the end). However it is quite logical in this sense that it checks if at least one of the items (that is any) in a list (set, collection) matches a single value.
Try with Contains function;
Determines whether a sequence contains a specified element.
var allowedStatus = new[]{ "A", "B", "C" };
var filteredOrders = orders.Order.Where(o => allowedStatus.Contains(o.StatusCode));
Just be careful, .Contains() will match any substring including the string that you do not expect. For eg. new[] { "A", "B", "AA" }.Contains("A") will return you both A and AA which you might not want. I have been bitten by it.
.Any() or .Exists() is safer choice
