Determine if Any or All Elements in a Sequence Satisfy a Condition

 

The All<TSource> operator returns true if all elements in a sequence satisfy a condition.

The Any<TSource> operator returns true if any element in a sequence satisfies a condition.

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.

            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);
                }
            }

Query Examples

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