101个Linq的例子

Where - Simple 1

筛选出数值中大于5的元素

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

筛选出所有没有现货的产品

 public void Linq2()
    {
        List<Product> products = GetProductList(); 

        var soldOutProducts =
            from p in products
            where p.UnitsInStock ==
            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

筛选充所有产品中有现货并且价格大于3的产品

 public void Linq3()
    {
        List<Product> products = GetProductList(); 

        var expensiveInStockProducts =
            from p in products
            where p.UnitsInStock >  && 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. 

Where - Drilldown

筛选中在华盛顿的所有客户，显示出他们的订单单号和订单日期

 public void Linq4()
    {
        List<Customer> 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

Where - Indexed

筛选出字符串长度小于自己索引的元素

 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.

 

Select - Simple 1

public void Linq6()
{
    int[] numbers = { , , , , , , , , ,  }; 

    var numsPlusOne =
        from n in numbers
        select n + ; 

    Console.WriteLine("Numbers + 1:");
    foreach (var i in numsPlusOne)
    {
        Console.WriteLine(i);
    }
}

Result

Numbers + 1:
6
5
2
4
10
9
7
8
3
1

Select - Simple 2

public void Linq7()
{
    List<Product> products = GetProductList(); 

    var productNames =
        from p in products
        select p.ProductName; 

    Console.WriteLine("Product Names:");
    foreach (var productName in productNames)
    {
        Console.WriteLine(productName);
    }
}

Result

Product Names:
Chai
Chang
Aniseed Syrup
Chef Anton's Cajun Seasoning
Chef Anton's Gumbo Mix
Grandma's Boysenberry Spread
Uncle Bob's Organic Dried Pears
Northwoods Cranberry Sauce
Mishi Kobe Niku
Ikura
Queso Cabrales
Queso Manchego La Pastora
Konbu
Tofu
Genen Shouyu
Pavlova
Alice Mutton
Carnarvon Tigers
Teatime Chocolate Biscuits
Sir Rodney's Marmalade

Select - Transformation

public void Linq8()
{
    int[] numbers = { , , , , , , , , ,  };
    string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 

    var textNums =
        from n in numbers
        select strings[n]; 

    Console.WriteLine("Number strings:");
    foreach (var s in textNums)
    {
        Console.WriteLine(s);
    }
}

Result

Number strings:
five
four
one
three
nine
eight
six
seven
two
zero

Select - Anonymous Types 1

public void Linq9()
{
    string[] words = { "aPPLE", "BlUeBeRrY", "cHeRry" }; 

    var upperLowerWords =
        from w in words
        select new { Upper = w.ToUpper(), Lower = w.ToLower() }; 

    foreach (var ul in upperLowerWords)
    {
        Console.WriteLine("Uppercase: {0}, Lowercase: {1}", ul.Upper, ul.Lower);
    }
}

Result

Uppercase: APPLE, Lowercase: apple
Uppercase: BLUEBERRY, Lowercase: blueberry
Uppercase: CHERRY, Lowercase: cherry

Select - Anonymous Types 2

public void Linq10()
{
    int[] numbers = { , , , , , , , , ,  };
    string[] strings = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 

    var digitOddEvens =
        from n in numbers
        select new { Digit = strings[n], Even = (n %  == ) }; 

    foreach (var d in digitOddEvens)
    {
        Console.WriteLine("The digit {0} is {1}.", d.Digit, d.Even ? "even" : "odd");
    }
}

Result

The digit five is odd.
The digit four is even.
The digit one is odd.
The digit three is odd.
The digit nine is odd.
The digit eight is even.
The digit six is even.
The digit seven is odd.
The digit two is even.
The digit zero is even.

Select - Anonymous Types 3

public void Linq11()
{
    List<Product> products = GetProductList(); 

    var productInfos =
        from p in products
        select new { p.ProductName, p.Category, Price = p.UnitPrice }; 

    Console.WriteLine("Product Info:");
    foreach (var productInfo in productInfos)
    {
        Console.WriteLine("{0} is in the category {1} and costs {2} per unit.", productInfo.ProductName, productInfo.Category, productInfo.Price);
    }
}

Result

Product Info:
Chai is in the category Beverages and costs 18.0000 per unit.
Chang is in the category Beverages and costs 19.0000 per unit.
Aniseed Syrup is in the category Condiments and costs 10.0000 per unit.
Chef Anton's Cajun Seasoning is in the category Condiments and costs 22.0000 per unit.
Chef Anton's Gumbo Mix is in the category Condiments and costs 21.3500 per unit.
Grandma's Boysenberry Spread is in the category Condiments and costs 25.0000 per unit.
Uncle Bob's Organic Dried Pears is in the category Produce and costs 30.0000 per unit.
Northwoods Cranberry Sauce is in the category Condiments and costs 40.0000 per unit.
Mishi Kobe Niku is in the category Meat/Poultry and costs 97.0000 per unit.
Ikura is in the category Seafood and costs 31.0000 per unit.
Queso Cabrales is in the category Dairy Products and costs 21.0000 per unit.
Queso Manchego La Pastora is in the category Dairy Products and costs 38.0000 per unit.
Konbu is in the category Seafood and costs 6.0000 per unit.
Tofu is in the category Produce and costs 23.2500 per unit.

Select - Indexed

public void Linq12()
{
    int[] numbers = { , , , , , , , , ,  }; 

    var numsInPlace = numbers.Select((num, index) => new { Num = num, InPlace = (num == index) }); 

    Console.WriteLine("Number: In-place?");
    foreach (var n in numsInPlace)
    {
        Console.WriteLine("{0}: {1}", n.Num, n.InPlace);
    }
}

Result

Number: In-place?
5: False
4: False
1: False
3: True
9: False
8: False
6: True
7: True
2: False
0: False

Select - Filtered

public void Linq13()
{
    int[] numbers = { , , , , , , , , ,  };
    string[] digits = { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; 

    var lowNums =
        from n in numbers
        where n <
        select digits[n]; 

    Console.WriteLine("Numbers < 5:");
    foreach (var num in lowNums)
    {
        Console.WriteLine(num);
    }
}

Result

Numbers < 5:
four
one
three
two
zero

SelectMany - Compound from 1

public void Linq14()
{
    int[] numbersA = { , , , , , ,  };
    int[] numbersB = { , , , ,  }; 

    var pairs =
        from a in numbersA
        from b in numbersB
        where a < b
        select new { a, b }; 

    Console.WriteLine("Pairs where a < b:");
    foreach (var pair in pairs)
    {
        Console.WriteLine("{0} is less than {1}", pair.a, pair.b);
    }
}

Result

Pairs where a < b:
0 is less than 1
0 is less than 3
0 is less than 5
0 is less than 7
0 is less than 8
2 is less than 3
2 is less than 5
2 is less than 7
2 is less than 8
4 is less than 5
4 is less than 7
4 is less than 8
5 is less than 7
5 is less than 8
6 is less than 7
6 is less than 8

SelectMany - Compound from 2

public void Linq15()
{
    List<Customer> customers = GetCustomerList(); 

    var orders =
        from c in customers
        from o in c.Orders
        where o.Total < 500.00M
        select new { c.CustomerID, o.OrderID, o.Total }; 

    ObjectDumper.Write(orders);
}

Result

CustomerID=ALFKI OrderID=10702 Total=330.00
CustomerID=ALFKI OrderID=10952 Total=471.20
CustomerID=ANATR OrderID=10308 Total=88.80
CustomerID=ANATR OrderID=10625 Total=479.75
CustomerID=ANATR OrderID=10759 Total=320.00
CustomerID=ANTON OrderID=10365 Total=403.20
CustomerID=ANTON OrderID=10682 Total=375.50
CustomerID=AROUT OrderID=10355 Total=480.00

SelectMany - Compound from 3

public void Linq16()
{
    List<Customer> customers = GetCustomerList(); 

    var orders =
        from c in customers
        from o in c.Orders
        where o.OrderDate >= new DateTime(, , )
        select new { c.CustomerID, o.OrderID, o.OrderDate }; 

    ObjectDumper.Write(orders);
}

Result

CustomerID=ALFKI OrderID=10835 OrderDate=1/15/1998
CustomerID=ALFKI OrderID=10952 OrderDate=3/16/1998
CustomerID=ALFKI OrderID=11011 OrderDate=4/9/1998
CustomerID=ANATR OrderID=10926 OrderDate=3/4/1998
CustomerID=ANTON OrderID=10856 OrderDate=1/28/1998
CustomerID=AROUT OrderID=10864 OrderDate=2/2/1998
CustomerID=AROUT OrderID=10920 OrderDate=3/3/1998
CustomerID=AROUT OrderID=10953 OrderDate=3/16/1998
CustomerID=AROUT OrderID=11016 OrderDate=4/10/1998
CustomerID=BERGS OrderID=10837 OrderDate=1/16/1998

SelectMany - from Assignment

public void Linq17()
{
    List<Customer> customers = GetCustomerList(); 

    var orders =
        from c in customers
        from o in c.Orders
        where o.Total >= 2000.0M
        select new { c.CustomerID, o.OrderID, o.Total }; 

    ObjectDumper.Write(orders);
}

Result

CustomerID=ANTON OrderID=10573 Total=2082.00
CustomerID=AROUT OrderID=10558 Total=2142.90
CustomerID=AROUT OrderID=10953 Total=4441.25
CustomerID=BERGS OrderID=10384 Total=2222.40
CustomerID=BERGS OrderID=10524 Total=3192.65
CustomerID=BERGS OrderID=10672 Total=3815.25
CustomerID=BERGS OrderID=10857 Total=2048.21
CustomerID=BLONP OrderID=10360 Total=7390.20
CustomerID=BOLID OrderID=10801 Total=3026.85
CustomerID=BONAP OrderID=10340 Total=2436.18
CustomerID=BONAP OrderID=10511 Total=2550.00
CustomerID=BOTTM OrderID=10742 Total=3118.00
CustomerID=BOTTM OrderID=10949 Total=4422.00
CustomerID=CHOPS OrderID=10519 Total=2314.20
CustomerID=CHOPS OrderID=10746 Total=2311.70
CustomerID=COMMI OrderID=10290 Total=2169.00

SelectMany - Multiple from

public void Linq18()
{
    List<Customer> customers = GetCustomerList(); 

    DateTime cutoffDate = new DateTime(, , ); 

    var orders =
        from c in customers
        where c.Region == "WA"
        from o in c.Orders
        where o.OrderDate >= cutoffDate
        select new { c.CustomerID, o.OrderID }; 

    ObjectDumper.Write(orders);
}

Result

CustomerID=LAZYK OrderID=10482
CustomerID=LAZYK OrderID=10545
CustomerID=TRAIH OrderID=10574
CustomerID=TRAIH OrderID=10577
CustomerID=TRAIH OrderID=10822
CustomerID=WHITC OrderID=10469
CustomerID=WHITC OrderID=10483
CustomerID=WHITC OrderID=10504
CustomerID=WHITC OrderID=10596
CustomerID=WHITC OrderID=10693
CustomerID=WHITC OrderID=10696
CustomerID=WHITC OrderID=10723
CustomerID=WHITC OrderID=10740

SelectMany - Indexed

public void Linq19()
{
    List<Customer> customers = GetCustomerList(); 

    var customerOrders =
        customers.SelectMany(
            (cust, custIndex) =>
            cust.Orders.Select(o => "Customer #" + (custIndex + ) +
                                    " has an order with OrderID " + o.OrderID)); 

    ObjectDumper.Write(customerOrders);
}

Result

Customer #1 has an order with OrderID 10643
Customer #1 has an order with OrderID 10692
Customer #1 has an order with OrderID 10702
Customer #1 has an order with OrderID 10835
Customer #1 has an order with OrderID 10952
Customer #1 has an order with OrderID 11011
Customer #2 has an order with OrderID 10308
Customer #2 has an order with OrderID 10625
Customer #2 has an order with OrderID 10759
Customer #2 has an order with OrderID 10926

...
Customer #90 has an order with OrderID 10248
Customer #90 has an order with OrderID 10615
Customer #90 has an order with OrderID 10673
Customer #90 has an order with OrderID 10695
Customer #90 has an order with OrderID 10873
Customer #90 has an order with OrderID 10879
Customer #90 has an order with OrderID 10910
Customer #90 has an order with OrderID 11005
Customer #91 has an order with OrderID 10374
Customer #91 has an order with OrderID 10611
Customer #91 has an order with OrderID 10792
Customer #91 has an order with OrderID 10870
Customer #91 has an order with OrderID 10906
Customer #91 has an order with OrderID 10998
Customer #91 has an order with OrderID 11044