LINQ查询表达式---------where子句

LINQ查询表达式---------where子句

where 子句用在查询表达式中，用于指定将在查询表达式中返回数据源中的哪些元素。 它将一个布尔条件（“谓词”）应用于每个源元素（由范围变量引用），并返回满足指定条件的元素。 一个查询表达式可以包含多个 where 子句，一个子句可以包含多个谓词子表达式。

1.1 常见的where子句查询

static void Main(string[] args)
{
    int[] numbers = { , , , , , , , , ,  };

    var num1 = from n in numbers
               where n >
               select n;

    foreach (var i in num1)
    {
        Console.Write(i + "  ");
    }

    Console.Write("\n");
    Console.WriteLine("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");

    var num2 = from n in numbers
               where n >
               where n %  ==
               select n;

    foreach (var i in num2)
    {
        Console.Write(i + "  ");
    }

    Console.Write("\n");
    Console.WriteLine("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");

    var num3 = from n in numbers
               where n >  && n <
               select n;

    foreach (var i in num3)
    {
        Console.Write(i + "  ");
    }

    Console.Write("\n");
    Console.WriteLine("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");

    var num4 = from n in numbers
               where (n ==  || n < ) && (n != )
               select n;

    foreach (var i in num4)
    {
        Console.Write(i + "  ");
    }

    Console.ReadLine();
}

输出结果：
9  7  8  6
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
8  6
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7  8  6
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5  8  3  4  6  2  1  0

1.2 在where子句中用自定义函数

static void Main(string[] args)
{
    int[] numbers = { , , , , , , , , ,  };

    var num = from n in numbers
              where IsEva(n)
              select n;

    foreach (var i in num)
    {
        Console.Write(i + "  ");
    }

    Console.ReadLine();
}

public static bool IsEva(int i)
{
    if (i %  == )
        return true;
    else
        return false;
}

查询结果：
8  4  6  2  0

1.3 动态微词的筛选

static void Main(string[] args)
{
    int[] numbers = { , , , , , , , , ,  };

    //定义动态的谓词数组，这个数组应该由实际运行环境生成
    int[] number = { , , , ,  };

    //查询在给定谓词数组里不存在的数字
    var num = from n in numbers
              where !number.Contains(n)
              select n;

    foreach (var i in num)
    {
        Console.Write(i + "  ");
    }

    Console.ReadLine();
}

输出结果：
9  8  4  6  2