How to: Determine if Any or All Elements in a Sequence Satisfy a Condition (LINQ to SQL)
The All<TSource> operator returns true if all elements in a sequence satisfy a condition.
The Any operator returns true if any element in a sequence satisfies a condition.
Example
The following example returns a sequence of customers that have at least one order. The Where/where clause evaluates to true if the given Customer has any Order.
Dim OrdersQuery = _
From cust In db.Customers _
Where cust.Orders.Any() _
Select cust
var OrdersQuery =
from cust in db.Customers
where cust.Orders.Any()
select cust;
The following Visual Basic code determines the list of customers who have not placed orders, and ensures that for every customer in that list, a contact name is provided.
Public Sub ContactsAvailable()
Dim db As New Northwnd("c:\northwnd.mdf")
Dim result = _
(From cust In db.Customers _
Where Not cust.Orders.Any() _
Select cust).All(AddressOf ContactAvailable)
If result Then
Console.WriteLine _
("All of the customers who have made no orders have a contact name")
Else
Console.WriteLine _
("Some customers who have made no orders have no contact name")
End If
End Sub
Function ContactAvailable(ByVal contact As Object) As Boolean
Dim cust As Customer = CType(contact, Customer)
Return (cust.ContactTitle Is Nothing OrElse _
cust.ContactTitle.Trim().Length = 0)
End Function
The following C# example returns a sequence of customers whose orders have a ShipCity beginning with "C". Also included in the return are customers who have no orders. (By design, the All<TSource> operator returns true for an empty sequence.) Customers with no orders are eliminated in the console output by using the Count operator.
var custEmpQuery =
from cust in db.Customers
where cust.Orders.All(o => o.ShipCity.StartsWith("C"))
orderby cust.CustomerID
select cust;
foreach (Customer custObj in custEmpQuery)
{
if (custObj.Orders.Count > 0)
Console.WriteLine("CustomerID: {0}", custObj.CustomerID);
foreach (Order ordObj in custObj.Orders)
{
Console.WriteLine("\t OrderID: {0}; ShipCity: {1}",
ordObj.OrderID, ordObj.ShipCity);
}
}