101个linq例子

101个linq例子
FirstOrDefault - Simple
```
public void Linq61() 
  
{ 
    int[] numbers = { }; 
  
    int firstNumOrDefault = numbers.FirstOrDefault(); 
  
    Console.WriteLine(firstNumOrDefault); 
}
```
Result

0

FirstOrDefault - Condition
```
public void Linq62() 
{ 
    List<Product> products = GetProductList(); 
  
    Product product789 = products.FirstOrDefault(p => p.ProductID == 789); 
 
    Console.WriteLine("Product 789 exists: {0}", product789 != null); 
}
```
Result

Product 789 exists: False

ElementAt
```
public void Linq64() 
{ 
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 
  
    int fourthLowNum = ( 
        from n in numbers 
        where n > 5 
        select n) 
        .ElementAt(1);  // 第二个数字的索引是 1，因为序列使用基于 0 的索引
 
    Console.WriteLine("Second number > 5: {0}", fourthLowNum); 
}
```
Result

Second number > 5: 8

Any - Simple

此示例使用 Any 确定是否任何单词数组中包含的子字符串 ei。
```
public void Linq67() 
{ 
    string[] words = { "believe", "relief", "receipt", "field" }; 
  
    bool iAfterE = words.Any(w => w.Contains("ei")); 
 
    Console.WriteLine("There is a word that contains in the list that contains 'ei': {0}", iAfterE); 
}
```
Result

There is a word that contains in the list that contains 'ei': True

Any - Grouped

此示例使用 Any 返回分组的产品仅供有缺货的至少一个产品的类别列表。
```
public void Linq69() 
{ 
    List<Product> products = GetProductList(); 
    var productGroups = 
        from p in products 
        group p by p.Category into g 
        where g.Any(p => p.UnitsInStock == 0) 
        select new { Category = g.Key, Products = g }; 
 
    ObjectDumper.Write(productGroups, 1);  
}
```
Result

Category=Condiments    Products=...
  Products: ProductID=3  ProductName=Aniseed Syrup      Category=Condiments    UnitPrice=10.0000      UnitsInStock=13
  Products: ProductID=4  ProductName=Chef Anton's Cajun Seasoning        Category=Condiments    UnitPrice=22.0000      UnitsInStock=53
  Products: ProductID=5  ProductName=Chef Anton's Gumbo Mix      Category=Condiments    UnitPrice=21.3500      UnitsInStock=0
  Products: ProductID=6  ProductName=Grandma's Boysenberry Spread        Category=Condiments    UnitPrice=25.0000      UnitsInStock=120
  Products: ProductID=8  ProductName=Northwoods Cranberry Sauce  Category=Condiments    UnitPrice=40.0000      UnitsInStock=6
  Products: ProductID=15  ProductName=Genen Shouyu        Category=Condiments    UnitPrice=15.5000      UnitsInStock=39
  Products: ProductID=44  ProductName=Gula Malacca        Category=Condiments    UnitPrice=19.4500      UnitsInStock=27
  Products: ProductID=61  ProductName=Sirop d'Ã©rable      Category=Condiments    UnitPrice=28.5000      UnitsInStock=113
  Products: ProductID=63  ProductName=Vegie-spread        Category=Condiments    UnitPrice=43.9000      UnitsInStock=24
  Products: ProductID=65  ProductName=Louisiana Fiery Hot Pepper Sauce    Category=Condiments    UnitPrice=21.0500      UnitsInStock=76
  Products: ProductID=66  ProductName=Louisiana Hot Spiced Okra  Category=Condiments    UnitPrice=17.0000      UnitsInStock=4
  Products: ProductID=77  ProductName=Original Frankfurter grÃ¼ne SoÃŸe    Category=Condiments    UnitPrice=13.0000      UnitsInStock=32
Category=Meat/Poultry  Products=...
  Products: ProductID=9  ProductName=Mishi Kobe Niku    Category=Meat/Poultry  UnitPrice=97.0000      UnitsInStock=29
  Products: ProductID=17  ProductName=Alice Mutton        Category=Meat/Poultry  UnitPrice=39.0000      UnitsInStock=0
  Products: ProductID=29  ProductName=ThÃ¼ringer Rostbratwurst    Category=Meat/Poultry  UnitPrice=123.7900      UnitsInStock=0
  Products: ProductID=53  ProductName=Perth Pasties      Category=Meat/Poultry  UnitPrice=32.8000      UnitsInStock=0
  Products: ProductID=54  ProductName=TourtiÃ¨re  Category=Meat/Poultry  UnitPrice=7.4500        UnitsInStock=21
  Products: ProductID=55  ProductName=PÃ¢tÃ© chinois        Category=Meat/Poultry  UnitPrice=24.0000      UnitsInStock=115
Category=Dairy Products        Products=...
  Products: ProductID=11  ProductName=Queso Cabrales      Category=Dairy Products        UnitPrice=21.0000      UnitsInStock=22
  Products: ProductID=12  ProductName=Queso Manchego La Pastora  Category=Dairy Products        UnitPrice=38.0000      UnitsInStock=86
  Products: ProductID=31  ProductName=Gorgonzola Telino  Category=Dairy Products        UnitPrice=12.5000      UnitsInStock=0
  Products: ProductID=32  ProductName=Mascarpone Fabioli  Category=Dairy Products        UnitPrice=32.0000      UnitsInStock=9
  Products: ProductID=33  ProductName=Geitost    Category=Dairy Products        UnitPrice=2.5000        UnitsInStock=112
  Products: ProductID=59  ProductName=Raclette Courdavault        Category=Dairy Products        UnitPrice=55.0000      UnitsInStock=79
  Products: ProductID=60  ProductName=Camembert Pierrot  Category=Dairy Products        UnitPrice=34.0000      UnitsInStock=19
  Products: ProductID=69  ProductName=Gudbrandsdalsost    Category=Dairy Products        UnitPrice=36.0000      UnitsInStock=26
  Products: ProductID=71  ProductName=Flotemysost        Category=Dairy Products        UnitPrice=21.5000      UnitsInStock=26
  Products: ProductID=72  ProductName=Mozzarella di Giovanni      Category=Dairy Products        UnitPrice=34.8000      UnitsInStock=14

All - Simple

此示例使用 All 来确定数组是否包含偶数。
```
public void Linq70() 
{  
    int[] numbers = { 1, 11, 3, 19, 41, 65, 19 }; 
  
    bool onlyOdd = numbers.All(n => n % 2 == 1); 
  
    Console.WriteLine("The list contains only odd numbers: {0}", onlyOdd); 
}
```
Result

The list contains only odd numbers: True

All - Grouped
```
public void Linq72() 
{ 
    List<Product> products = GetProductList(); 
  
    var productGroups = 
        from p in products 
        group p by p.Category into g 
        where g.All(p => p.UnitsInStock > 0) 
        select new { Category = g.Key, Products = g }; 
     
    ObjectDumper.Write(productGroups, 1); 
}
```
Result

Category=Beverages      Products=...
  Products: ProductID=1  ProductName=Chai        Category=Beverages      UnitPrice=18.0000      UnitsInStock=39
  Products: ProductID=2  ProductName=Chang      Category=Beverages      UnitPrice=19.0000      UnitsInStock=17
  Products: ProductID=24  ProductName=GuaranÃ¡ FantÃ¡stica  Category=Beverages      UnitPrice=4.5000        UnitsInStock=20
  Products: ProductID=34  ProductName=Sasquatch Ale      Category=Beverages      UnitPrice=14.0000      UnitsInStock=111
  Products: ProductID=35  ProductName=Steeleye Stout      Category=Beverages      UnitPrice=18.0000      UnitsInStock=20
  Products: ProductID=38  ProductName=CÃ´te de Blaye      Category=Beverages      UnitPrice=263.5000      UnitsInStock=17
  Products: ProductID=39  ProductName=Chartreuse verte    Category=Beverages      UnitPrice=18.0000      UnitsInStock=69
  Products: ProductID=43  ProductName=Ipoh Coffee        Category=Beverages      UnitPrice=46.0000      UnitsInStock=17
  Products: ProductID=67  ProductName=Laughing Lumberjack Lager  Category=Beverages      UnitPrice=14.0000      UnitsInStock=52
  Products: ProductID=70  ProductName=Outback Lager      Category=Beverages      UnitPrice=15.0000      UnitsInStock=15
  Products: ProductID=75  ProductName=RhÃ¶nbrÃ¤u Klosterbier        Category=Beverages      UnitPrice=7.7500        UnitsInStock=125
  Products: ProductID=76  ProductName=LakkalikÃ¶Ã¶ri        Category=Beverages      UnitPrice=18.0000      UnitsInStock=57

Count - Simple

获取列表中没有重复的元素数量
```
public void Linq73() 
{ 
    int[] factorsOf300 = { 2, 2, 3, 5, 5 }; 
  
    int uniqueFactors = factorsOf300.Distinct().Count(); 
  
    Console.WriteLine("There are {0} unique factorsof300.", uniqueFactors); 
}
```
Result

There are 3 unique factorsof300.

Count - Nested
```
public void Linq76() 
{ 
    List<Customer> customers = GetCustomerList(); 
  
    var orderCounts = 
        from c in customers 
        select new { c.CustomerID, OrderCount = c.Orders.Count() }; 
  
    ObjectDumper.Write(orderCounts); 
}
```
Result
CustomerID=ALFKI OrderCount=6
CustomerID=ANATR OrderCount=4
CustomerID=ANTON OrderCount=7
CustomerID=AROUT OrderCount=13
CustomerID=BERGS OrderCount=18

Count - Grouped
```
public void Linq77() 
{ 
    List<Product> products = GetProductList(); 
  
    var categoryCounts = 
        from p in products 
        group p by p.Category into g 
        select new { Category = g.Key, ProductCount = g.Count() }; 
  
    ObjectDumper.Write(categoryCounts 
}
```
Result
Category=Beverages ProductCount=12
Category=Condiments ProductCount=5
Category=Produce ProductCount=6
Category=Meat/Poultry ProductCount=12
Category=Seafood ProductCount=10
Category=Dairy Products ProductCount=13
Category=Confections ProductCount=7
Category=Grains/Cereals ProductCount=12

Sum - Simple
```
public void Linq78() 
{ 
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 
  
    double numSum = numbers.Sum(); 
  
    Console.WriteLine("The sum of the numbers is {0}.", numSum); 
}
```
Result

The sum of the numbers is 45.

Sum - Projection
```
public void Linq79() 
{ 
    string[] words = { "cherry", "apple", "blueberry" }; 
  
    double totalChars = words.Sum(w => w.Length); 
  
    Console.WriteLine("There are a total of {0} characters in these words.", totalChars); 
}
```
Result

There are a total of 20 characters in these words.

Sum - Grouped
```
public void Linq80() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        select new { Category = g.Key, TotalUnitsInStock = g.Sum(p => p.UnitsInStock) }; 
  
    ObjectDumper.Write(categories); 
}
```
Result
Category=Beverages TotalUnitsInStock=559
Category=Condiments TotalUnitsInStock=507
Category=Produce TotalUnitsInStock=100
Category=Meat/Poultry TotalUnitsInStock=165
Category=Seafood TotalUnitsInStock=701
Category=Dairy Products TotalUnitsInStock=393
Category=Confections TotalUnitsInStock=386
Category=Grains/Cereals TotalUnitsInStock=308

Min - Simple
```
public void Linq81() 
{ 
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 
  
    int minNum = numbers.Min(); 
  
    Console.WriteLine("The minimum number is {0}.", minNum); 
}
```
Result

The minimum number is 0.

Min - Projection
```
ublic void Linq82() 
{ 
    string[] words = { "cherry", "apple", "blueberry" }; 
  
    int shortestWord = words.Min(w => w.Length); 
  
    Console.WriteLine("The shortest word is {0} characters long.", shortestWord); 
}
```
Result

The shortest word is 5 characters long.

Min - Grouped
```
public void Linq83() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        select new { Category = g.Key, CheapestPrice = g.Min(p => p.UnitPrice) }; 
  
    ObjectDumper.Write(categories); 
}
```
Result
Category=Beverages CheapestPrice=4.5000
Category=Condiments CheapestPrice=10.0000
Category=Produce CheapestPrice=10.0000
Category=Meat/Poultry CheapestPrice=7.4500
Category=Seafood CheapestPrice=6.0000
Category=Dairy Products CheapestPrice=2.5000
Category=Confections CheapestPrice=9.2000
Category=Grains/Cereals CheapestPrice=7.0000

Min - Elements
```
public void Linq84() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        let minPrice = g.Min(p => p.UnitPrice) 
        select new { Category = g.Key, CheapestProducts = g.Where(p => p.UnitPrice == minPrice) }; 
  
    ObjectDumper.Write(categories, 1); 
}
```
Result

Category=Beverages      CheapestProducts=...
  CheapestProducts: ProductID=24  ProductName=GuaranÃ¡ FantÃ¡stica  Category=Beverages      UnitPrice=4.5000        UnitsInStock=20
Category=Condiments    CheapestProducts=...
  CheapestProducts: ProductID=3  ProductName=Aniseed Syrup      Category=Condiments    UnitPrice=10.0000      UnitsInStock=13
Category=Produce        CheapestProducts=...
  CheapestProducts: ProductID=74  ProductName=Longlife Tofu      Category=Produce        UnitPrice=10.0000      UnitsInStock=4
Category=Meat/Poultry  CheapestProducts=...
  CheapestProducts: ProductID=54  ProductName=TourtiÃ¨re  Category=Meat/Poultry  UnitPrice=7.4500        UnitsInStock=21
Category=Seafood        CheapestProducts=...
  CheapestProducts: ProductID=13  ProductName=Konbu      Category=Seafood        UnitPrice=6.0000        UnitsInStock=24
Category=Dairy Products        CheapestProducts=...
  CheapestProducts: ProductID=33  ProductName=Geitost    Category=Dairy Products        UnitPrice=2.5000        UnitsInStock=112
Category=Confections    CheapestProducts=...
  CheapestProducts: ProductID=19  ProductName=Teatime Chocolate Biscuits  Category=Confections    UnitPrice=9.2000        UnitsInStock=25
Category=Grains/Cereals        CheapestProducts=...
  CheapestProducts: ProductID=52  ProductName=Filo Mix    Category=Grains/Cereals        UnitPrice=7.0000        UnitsInStock=38

Max - Simple
```
public void Linq85() 
{ 
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 
  
    int maxNum = numbers.Max(); 
  
    Console.WriteLine("The maximum number is {0}.", maxNum); 
}
```
Result

The maximum number is 9.

Max - Projection
```
public void Linq86() 
{ 
    string[] words = { "cherry", "apple", "blueberry" }; 
  
    int longestLength = words.Max(w => w.Length); 
  
    Console.WriteLine("The longest word is {0} characters long.", longestLength); 
}
```
Result

The longest word is 9 characters long.

Max - Grouped
```
public void Linq87() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        select new { Category = g.Key, MostExpensivePrice = g.Max(p => p.UnitPrice) }; 
  
    ObjectDumper.Write(categories); 
}
```
Result
Category=Beverages MostExpensivePrice=263.5000
Category=Condiments MostExpensivePrice=43.9000
Category=Produce MostExpensivePrice=53.0000
Category=Meat/Poultry MostExpensivePrice=123.7900
Category=Seafood MostExpensivePrice=62.5000
Category=Dairy Products MostExpensivePrice=55.0000
Category=Confections MostExpensivePrice=81.0000
Category=Grains/Cereals MostExpensivePrice=38.0000

Max - Elements
```
public void Linq88() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        let maxPrice = g.Max(p => p.UnitPrice) 
        select new { Category = g.Key, MostExpensiveProducts = g.Where(p => p.UnitPrice == maxPrice) }; 
  
    ObjectDumper.Write(categories, 1); 
}
```
Result

Category=Beverages      MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=38    ProductName=CÃ´te de Blaye      Category=Beverages      UnitPrice=263.5000      UnitsInStock=17
Category=Condiments    MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=63    ProductName=Vegie-spread        Category=Condiments    UnitPrice=43.9000      UnitsInStock=24
Category=Produce        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=51    ProductName=Manjimup Dried Apples      Category=Produce        UnitPrice=53.0000      UnitsInStock=20
Category=Meat/Poultry  MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=29    ProductName=ThÃ¼ringer Rostbratwurst    Category=Meat/Poultry  UnitPrice=123.7900      UnitsInStock=0
Category=Seafood        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=18    ProductName=Carnarvon Tigers    Category=Seafood        UnitPrice=62.5000      UnitsInStock=42
Category=Dairy Products        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=59    ProductName=Raclette Courdavault        Category=Dairy Products        UnitPrice=55.0000      UnitsInStock=79
Category=Confections    MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=20    ProductName=Sir Rodney's Marmalade      Category=Confections    UnitPrice=81.0000      UnitsInStock=40
Category=Grains/Cereals        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=56    ProductName=Gnocchi di nonna Alice      Category=Grains/Cereals        UnitPrice=38.0000      UnitsInStock=21

Average - Simple
```
public void Linq89() 
{ 
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 
  
    double averageNum = numbers.Average(); 
  
    Console.WriteLine("The average number is {0}.", averageNum); 
}
```
Result

The average number is 4.5.

Average - Projection
```
public void Linq90() 
{ 
    string[] words = { "cherry", "apple", "blueberry" }; 
  
    double averageLength = words.Average(w => w.Length); 
  
    Console.WriteLine("The average word length is {0} characters.", averageLength); 
}
```
Result

The average word length is 6.66666666666667 characters.

Average - Grouped
```
public void Linq91() 
{ 
    List<Product> products = GetProductList(); 
  
    var categories = 
        from p in products 
        group p by p.Category into g 
        select new { Category = g.Key, AveragePrice = g.Average(p => p.UnitPrice) }; 
  
    ObjectDumper.Write(categories); 
}
```
Result

Category=Beverages AveragePrice=37.979166666666666666666666667
Category=Condiments AveragePrice=23.0625
Category=Produce AveragePrice=32.3700
Category=Meat/Poultry AveragePrice=54.006666666666666666666666667
Category=Seafood AveragePrice=20.6825
Category=Dairy Products AveragePrice=28.7300
Category=Confections AveragePrice=25.1600
Category=Grains/Cereals AveragePrice=20.2500

Aggregate - Simple

这个例子是数组中所有的元素相乘，求出最终的积
```
public void Linq92() 
{ 
    double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 }; 
  
    double product = doubles.Aggregate((runningProduct, nextFactor) => runningProduct * nextFactor); 
  
    Console.WriteLine("Total product of all numbers: {0}", product); 
}
```
Result

Total product of all numbers: 88.33081

Aggregate - Seed
```
public void Linq93() 
{ 
    double startBalance = 100.0; 
  
    int[] attemptedWithdrawals = { 20, 10, 40, 50, 10, 70, 30 }; 
  
    double endBalance = 
        attemptedWithdrawals.Aggregate(startBalance, 
            (balance, nextWithdrawal) => 
                ((nextWithdrawal <= balance) ? (balance - nextWithdrawal) : balance)); 
  
    Console.WriteLine("Ending balance: {0}", endBalance); 
}
```
Result

Ending balance: 20

Concat - 1

求二个集合的合集
```
public void Linq94() 
{ 
    int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
    int[] numbersB = { 1, 3, 5, 7, 8 }; 
  
    var allNumbers = numbersA.Concat(numbersB); 
  
    Console.WriteLine("All numbers from both arrays:"); 
    foreach (var n in allNumbers) 
    { 
        Console.WriteLine(n); 
    } 
}
```
Result

All numbers from both arrays: 0 2 4 5 6 8 9 1 3 5 7 8
Concat - 2
public void Linq95() { List<Customer> customers = GetCustomerList(); List<Product> products = GetProductList(); var customerNames = from c in customers select c.CompanyName; var productNames = from p in products select p.ProductName; var allNames = customerNames.Concat(productNames); Console.WriteLine("Customer and product names:"); foreach (var n in allNames) { Console.WriteLine(n); } }
Result

Customer and product names: Alfreds Futterkiste Ana Trujillo Emparedados y helados Antonio Moreno TaquerÃa Around the Horn Berglunds snabbkÃ¶p Blauer See Delikatessen Blondel pÃ¨re et fils BÃ³lido Comidas preparadas Bon app' Bottom-Dollar Markets B's Beverages Cactus Comidas para llevar Centro comercial Moctezuma Chop-suey Chinese ComÃ©rcio Mineiro Consolidated Holdings Drachenblut Delikatessen Du monde entier Eastern Connection Ernst Handel Familia Arquibaldo FISSA Fabrica Inter. Salchichas S.A. Folies gourmandes Folk och fÃ¤ HB Frankenversand France restauration
EqualAll - 1

public void Linq96() { var wordsA = new string[] { "cherry", "apple", "blueberry" }; var wordsB = new string[] { "cherry", "apple", "blueberry" }; bool match = wordsA.SequenceEqual(wordsB); Console.WriteLine("The sequences match: {0}", match); }

Result

The sequences match: True

EqualAll - 2

public void Linq97() { var wordsA = new string[] { "cherry", "apple", "blueberry" }; var wordsB = new string[] { "apple", "blueberry", "cherry" }; bool match = wordsA.SequenceEqual(wordsB); Console.WriteLine("The sequences match: {0}", match); }

Result

The sequences match: False

Combine

public static class CustomSequenceOperators { public static IEnumerable Combine(this IEnumerable first, IEnumerable second, Func func) { using (IEnumerator e1 = first.GetEnumerator(), e2 = second.GetEnumerator()) { while (e1.MoveNext() && e2.MoveNext()) { yield return func(e1.Current, e2.Current); } } } } public void Linq98() { int[] vectorA = { 0, 2, 4, 5, 6 }; int[] vectorB = { 1, 3, 5, 7, 8 }; int dotProduct = vectorA.Combine(vectorB, (a, b) => a * b).Sum(); Console.WriteLine("Dot product: {0}", dotProduct); }

Result

Dot product: 109

Deferred Execution

public void Linq99() { // Sequence operators form first-class queries that // are not executed until you enumerate over them. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int i = 0; var q = from n in numbers select ++i; // Note, the local variable 'i' is not incremented // until each element is evaluated (as a side-effect): foreach (var v in q) { Console.WriteLine("v = {0}, i = {1}", v, i); } }

Result

v = 1, i = 1
v = 2, i = 2
v = 3, i = 3
v = 4, i = 4
v = 5, i = 5
v = 6, i = 6
v = 7, i = 7
v = 8, i = 8
v = 9, i = 9
v = 10, i = 10

Immediate Execution

public void Linq100() { // Methods like ToList() cause the query to be // executed immediately, caching the results. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; int i = 0; var q = ( from n in numbers select ++i) .ToList(); // The local variable i has already been fully // incremented before we iterate the results: foreach (var v in q) { Console.WriteLine("v = {0}, i = {1}", v, i); } }

Result

v = 1, i = 10
v = 2, i = 10
v = 3, i = 10
v = 4, i = 10
v = 5, i = 10
v = 6, i = 10
v = 7, i = 10
v = 8, i = 10
v = 9, i = 10
v = 10, i = 10

Query Reuse

public void Linq101() { // Deferred execution lets us define a query once // and then reuse it later after data changes. int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var lowNumbers = from n in numbers where n <= 3 select n; Console.WriteLine("First run numbers <= 3:"); foreach (int n in lowNumbers) { Console.WriteLine(n); } for (int i = 0; i < 10; i++) { numbers[i] = -numbers[i]; } // During this second run, the same query object, // lowNumbers, will be iterating over the new state // of numbers[], producing different results: Console.WriteLine("Second run numbers <= 3:"); foreach (int n in lowNumbers) { Console.WriteLine(n); } }

Result

First run numbers <= 3:
1
3
2
0
Second run numbers <= 3:
-5
-4
-1
-3
-9
-8
-6
-7
-2
0

Cross Join

public void Linq102() { string[] categories = new string[]{ "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" }; List<Product> products = GetProductList(); var q = from c in categories join p in products on c equals p.Category select new { Category = c, p.ProductName }; foreach (var v in q) { Console.WriteLine(v.ProductName + ": " + v.Category); } }

Result

Chai: Beverages
Chang: Beverages
GuaranÃ¡ FantÃ¡stica: Beverages
Sasquatch Ale: Beverages
Steeleye Stout: Beverages
CÃ´te de Blaye: Beverages
Chartreuse verte: Beverages
Ipoh Coffee: Beverages
Laughing Lumberjack Lager: Beverages
Outback Lager: Beverages
RhÃ¶nbrÃ¤u Klosterbier: Beverages
LakkalikÃ¶Ã¶ri: Beverages
Aniseed Syrup: Condiments
Chef Anton's Cajun Seasoning: Condiments
Chef Anton's Gumbo Mix: Condiments
Grandma's Boysenberry Spread: Condiments
Northwoods Cranberry Sauce: Condiments
Genen Shouyu: Condiments
Gula Malacca: Condiments
Sirop d'Ã©rable: Condiments
Vegie-spread: Condiments

Group Join

public void Linq103() { string[] categories = new string[]{ "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" }; List<Product> products = GetProductList(); var q = from c in categories join p in products on c equals p.Category into ps select new { Category = c, Products = ps }; foreach (var v in q) { Console.WriteLine(v.Category + ":"); foreach (var p in v.Products) { Console.WriteLine(" " + p.ProductName); } } }

Result

Beverages:
Chai
Chang
GuaranÃ¡ FantÃ¡stica
Sasquatch Ale
Steeleye Stout
CÃ´te de Blaye
Chartreuse verte
Ipoh Coffee
Laughing Lumberjack Lager
Outback Lager
RhÃ¶nbrÃ¤u Klosterbier
LakkalikÃ¶Ã¶ri
Condiments:
Aniseed Syrup
Chef Anton's Cajun Seasoning
Chef Anton's Gumbo Mix
Grandma's Boysenberry Spread
Northwoods Cranberry Sauce

Cross Join with Group Join

public void Linq104() { string[] categories = new string[]{ "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" }; List<Product> products = GetProductList(); var q = from c in categories join p in products on c equals p.Category into ps from p in ps select new { Category = c, p.ProductName }; foreach (var v in q) { Console.WriteLine(v.ProductName + ": " + v.Category); } }

Result

Chai: Beverages
Chang: Beverages
GuaranÃ¡ FantÃ¡stica: Beverages
Sasquatch Ale: Beverages
Steeleye Stout: Beverages
CÃ´te de Blaye: Beverages
Chartreuse verte: Beverages
Ipoh Coffee: Beverages
Laughing Lumberjack Lager: Beverages
Outback Lager: Beverages
RhÃ¶nbrÃ¤u Klosterbier: Beverages
LakkalikÃ¶Ã¶ri: Beverages
Aniseed Syrup: Condiments
Chef Anton's Cajun Seasoning: Condiments
Chef Anton's Gumbo Mix: Condiments
Grandma's Boysenberry Spread: Condiments
Northwoods Cranberry Sauce: Condiments
Genen Shouyu: Condiments
Gula Malacca: Condiments
Sirop d'Ã©rable: Condiments
Vegie-spread: Condiments

Left Outer Join

public void Linq105() { string[] categories = new string[]{ "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" }; List<Product> products = GetProductList(); var q = from c in categories join p in products on c equals p.Category into ps from p in ps.DefaultIfEmpty() select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName }; foreach (var v in q) { Console.WriteLine(v.ProductName + ": " + v.Category); } }

Result

Chai: Beverages
Chang: Beverages
GuaranÃ¡ FantÃ¡stica: Beverages
Sasquatch Ale: Beverages
Steeleye Stout: Beverages
CÃ´te de Blaye: Beverages
Chartreuse verte: Beverages
Ipoh Coffee: Beverages
Laughing Lumberjack Lager: Beverages
Outback Lager: Beverages
RhÃ¶nbrÃ¤u Klosterbier: Beverages
LakkalikÃ¶Ã¶ri: Beverages
Aniseed Syrup: Condiments
Chef Anton's Cajun Seasoning: Condiments
Chef Anton's Gumbo Mix: Condiments
Grandma's Boysenberry Spread: Condiments
Northwoods Cranberry Sauce: Condiments
Genen Shouyu: Condiments
Gula Malacca: Condiments
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原文地址：https://www.cnblogs.com/fzhilong/p/4657106.html

FirstOrDefault - Simple

Result

FirstOrDefault - Condition

Result

ElementAt

Any - Simple

Result

Any - Grouped

Result

All - Simple

All - Grouped

Result

Count - Simple

Count - Nested

Count - Grouped

Sum - Simple

Sum - Projection

Sum - Grouped

Min - Simple

Min - Projection

Min - Grouped

Min - Elements

Max - Simple

Max - Projection

Max - Grouped

Max - Elements

Average - Simple

Average - Projection

Average - Grouped

Aggregate - Simple

Result

Aggregate - Seed

Result

Concat - 1

Concat - 2

EqualAll - 1

Result

EqualAll - 2

Result

Combine

Result

Deferred Execution

Immediate Execution

Result

Query Reuse

Cross Join

Result

Group Join

Result

Cross Join with Group Join

Result

Left Outer Join

Result