学习LinQ

LINQ是什么？
它是Language Integrated Query。
当我们要对数据库表进行查询的时候，我们一定会编写"select * from sometable where ID = .."的语句。好，那我们现在根据LINQ的语法，完全可以将我们熟悉的SQL中像"select","from","where"等语句在.NET Framework环境中顺利使用并且大大提高开发的效率。


例如：

public void Linq6() {
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };

    var numsPlusOne =
        from n in numbers
        select n + 1;
    
    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

再如：

public void Linq10() {
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
    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 % 2 == 0)};

    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.

还有：

public void Linq12() {
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };

    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