Restriction Operators
Where - Simple 1
This sample prints each element of an input integer array whose value is less than 5. The sample uses a query expression to create a new sequence of integers and then iterates over each element in the sequence, printing its value.
public void Linq1() {
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
var lowNums =
from n in numbers
where n < 5
select n;
Console.WriteLine("Numbers < 5:");
foreach (var x in lowNums) {
Console.WriteLine(x);
}
}
Result
Numbers < 5:
4
1
3
2
0
Where - Simple 2
This sample prints a list of all products that are out of stock. It selects each item from the product list where the number of units in stock equals zero.
public void Linq2() {
List products = GetProductList();
var soldOutProducts =
from p in products
where p.UnitsInStock == 0
select p;
Console.WriteLine("Sold out products:");
foreach (var product in soldOutProducts) {
Console.WriteLine("{0} is sold out!", product.ProductName);
}
}
Result
Sold out products:
Chef Anton's Gumbo Mix is sold out!
Alice Mutton is sold out!
Thüringer Rostbratwurst is sold out!
Gorgonzola Telino is sold out!
Perth Pasties is sold out!
Where - Simple 3
This sample lists all expensive items in stock. It uses a query expression that selects items from the product list where the number of items in stock is non-zero and the item's unit price is greater than 3.00
public void Linq3() {
List products = GetProductList();
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select p;
Console.WriteLine("In-stock products that cost more than 3.00:");
foreach (var product in expensiveInStockProducts) {
Console.WriteLine("{0} is in stock and costs more than 3.00.", product.ProductName);
}
}
Result
In-stock products that cost more than 3.00:
Chai is in stock and costs more than 3.00.
Chang is in stock and costs more than 3.00.
Aniseed Syrup is in stock and costs more than 3.00.
Chef Anton's Cajun Seasoning is in stock and costs more than 3.00.
Grandma's Boysenberry Spread is in stock and costs more than 3.00.
Uncle Bob's Organic Dried Pears is in stock and costs more than 3.00.
Northwoods Cranberry Sauce is in stock and costs more than 3.00.
Mishi Kobe Niku is in stock and costs more than 3.00.
Ikura is in stock and costs more than 3.00.
Queso Cabrales is in stock and costs more than 3.00.
Queso Manchego La Pastora is in stock and costs more than 3.00.
Konbu is in stock and costs more than 3.00.
Tofu is in stock and costs more than 3.00.
Genen Shouyu is in stock and costs more than 3.00.
Pavlova is in stock and costs more than 3.00.
Carnarvon Tigers is in stock and costs more than 3.00.
Teatime Chocolate Biscuits is in stock and costs more than 3.00.
Sir Rodney's Marmalade is in stock and costs more than 3.00.
Sir Rodney's Scones is in stock and costs more than 3.00.
Gustaf's Knäckebröd is in stock and costs more than 3.00.
Tunnbröd is in stock and costs more than 3.00.
Guaraná Fantástica is in stock and costs more than 3.00.
NuNuCa Nuá-Nougat-Creme is in stock and costs more than 3.00.
Gumbär Gummibärchen is in stock and costs more than 3.00.
Schoggi Schokolade is in stock and costs more than 3.00.
Rössle Sauerkraut is in stock and costs more than 3.00.
Nord-Ost Matjeshering is in stock and costs more than 3.00.
Mascarpone Fabioli is in stock and costs more than 3.00.
Sasquatch Ale is in stock and costs more than 3.00.
Steeleye Stout is in stock and costs more than 3.00.
Inlagd Sill is in stock and costs more than 3.00.
Gravad lax is in stock and costs more than 3.00.
Côte de Blaye is in stock and costs more than 3.00.
Chartreuse verte is in stock and costs more than 3.00.
Boston Crab Meat is in stock and costs more than 3.00.
Jack's New England Clam Chowder is in stock and costs more than 3.00.
Singaporean Hokkien Fried Mee is in stock and costs more than 3.00.
Ipoh Coffee is in stock and costs more than 3.00.
Gula Malacca is in stock and costs more than 3.00.
Rogede sild is in stock and costs more than 3.00.
Spegesild is in stock and costs more than 3.00.
Zaanse koeken is in stock and costs more than 3.00.
Chocolade is in stock and costs more than 3.00.
Maxilaku is in stock and costs more than 3.00.
Valkoinen suklaa is in stock and costs more than 3.00.
Manjimup Dried Apples is in stock and costs more than 3.00.
Filo Mix is in stock and costs more than 3.00.
Tourtière is in stock and costs more than 3.00.
Pâté chinois is in stock and costs more than 3.00.
Gnocchi di nonna Alice is in stock and costs more than 3.00.
Ravioli Angelo is in stock and costs more than 3.00.
Escargots de Bourgogne is in stock and costs more than 3.00.
Raclette Courdavault is in stock and costs more than 3.00.
Camembert Pierrot is in stock and costs more than 3.00.
Sirop d'érable is in stock and costs more than 3.00.
Tarte au sucre is in stock and costs more than 3.00.
Vegie-spread is in stock and costs more than 3.00.
Wimmers gute Semmelknödel is in stock and costs more than 3.00.
Louisiana Fiery Hot Pepper Sauce is in stock and costs more than 3.00.
Louisiana Hot Spiced Okra is in stock and costs more than 3.00.
Laughing Lumberjack Lager is in stock and costs more than 3.00.
Scottish Longbreads is in stock and costs more than 3.00.
Gudbrandsdalsost is in stock and costs more than 3.00.
Outback Lager is in stock and costs more than 3.00.
Flotemysost is in stock and costs more than 3.00.
Mozzarella di Giovanni is in stock and costs more than 3.00.
Röd Kaviar is in stock and costs more than 3.00.
Longlife Tofu is in stock and costs more than 3.00.
Rhönbräu Klosterbier is in stock and costs more than 3.00.
Lakkalikööri is in stock and costs more than 3.00.
Original Frankfurter grüne Soáe is in stock and costs more than 3.00.
Where - Drilldown
This sample prints a list of customers from the state of Washington along with their orders. A sequence of customers is created by selecting customers where the region is 'WA'. The sample uses doubly nested foreach statements to print the order numbers for each customer in the sequence.
public void Linq4() {
List customers = GetCustomerList();
var waCustomers =
from c in customers
where c.Region == "WA"
select c;
Console.WriteLine("Customers from Washington and their orders:");
foreach (var customer in waCustomers) {
Console.WriteLine("Customer {0}: {1}", customer.CustomerID, customer.CompanyName);
foreach (var order in customer.Orders) {
Console.WriteLine(" Order {0}: {1}", order.OrderID, order.OrderDate);
}
}
}
Result
Customers from Washington and their orders:
Customer LAZYK: Lazy K Kountry Store
Order 10482: 3/21/1997 12:00:00 AM
Order 10545: 5/22/1997 12:00:00 AM
Customer TRAIH: Trail's Head Gourmet Provisioners
Order 10574: 6/19/1997 12:00:00 AM
Order 10577: 6/23/1997 12:00:00 AM
Order 10822: 1/8/1998 12:00:00 AM
Customer WHITC: White Clover Markets
Order 10269: 7/31/1996 12:00:00 AM
Order 10344: 11/1/1996 12:00:00 AM
Order 10469: 3/10/1997 12:00:00 AM
Order 10483: 3/24/1997 12:00:00 AM
Order 10504: 4/11/1997 12:00:00 AM
Order 10596: 7/11/1997 12:00:00 AM
Order 10693: 10/6/1997 12:00:00 AM
Order 10696: 10/8/1997 12:00:00 AM
Order 10723: 10/30/1997 12:00:00 AM
Order 10740: 11/13/1997 12:00:00 AM
Order 10861: 1/30/1998 12:00:00 AM
Order 10904: 2/24/1998 12:00:00 AM
Order 11032: 4/17/1998 12:00:00 AM
Order 11066: 5/1/1998 12:00:00 AM
Where - Indexed
This sample uses an indexed Where clause to print the name of each number, from 0-9, where the length of the number's name is shorter than its value. In this case, the code is passing a lamda expression which is converted to the appropriate delegate type. The body of the lamda expression tests whether the length of the string is less than its index in the array.
public void Linq5() {
string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" };
var shortDigits = digits.Where((digit, index) => digit.Length < index);
Console.WriteLine("Short digits:");
foreach (var d in shortDigits) {
Console.WriteLine("The word {0} is shorter than its value.", d);
}
}
Result
Short digits:
The word five is shorter than its value.
The word six is shorter than its value.
The word seven is shorter than its value.
The word eight is shorter than its value.
The word nine is shorter than its value.
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