运用Linq操作对象示例

Java和C++对于容器中元素的操作已经十分简便智能了，但与C#相比，简直弱爆了。这正是因为C#拥有一个利器：Linq。简单的说，Linq就是利用类SQL语句来操作容器中的元素。这样就完全放弃了编程的思维方式，而采用浅显易懂的数据库操作了。这不得不说是一次重大的突破，不过同时也让C#程序员越来越懒，失去了程序员的血性。

下面简单举个例子，说明Linq的用法。

1、定义一个Person类，包括ID,Nam,Age三个属性。

class Person
{
    public Person(int id, string name, int age)
    {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    private int id;

    // Person ID
    public int PersonID
    {
        get { return this.id; }
        set { this.id = value; }
    }

    private string name;

    // Person name
    public string Name
    {
        get { return this.name; }
        set { this.name = value; }
    }

    public int age;

    // Age that ranges from 1 to 100
    public int Age
    {
        get { return this.age; }
        set
        {
            if (value > 0 && value <= 100)
                this.age = value;
            else
                throw new Exception("Age is out of scope [1,100]");
        }
    }
}

2、创建一个List<Person>作为数据源

// Build the Person List as data source
List<Person> persons = new List<Person>();

persons.Add(new Person(1, "Alexander David", 20));
persons.Add(new Person(2, "Aziz Hassouneh", 18));
persons.Add(new Person(3, "Guido Pica", 20));
persons.Add(new Person(4, "Chris Preston", 19));
persons.Add(new Person(5, "Jorgen Rahgek", 20));
persons.Add(new Person(6, "Todd Rowe", 18));
persons.Add(new Person(7, "SPeter addow", 22));
persons.Add(new Person(8, "Markus Breyer", 19));
persons.Add(new Person(9, "Scott Brown", 20));

3、查询

// query a person in the data source.
var Todd = (from p in persons
            where p.Name == "Todd Rowe"
            select p).First();
Console.WriteLine("Todd Rowe's age is {0}", Todd.Age);

4、更新

// update person's age
Todd.Age = 21;
Console.WriteLine("Todd Rowe's age is updated to {0}", (from p in persons
                                                    where p.Name == "Todd Rowe"
                                                    select p).First().Age);

5、排序并输出

// sort by person's age
var query1 = from p in persons
                orderby p.Age
                select p;
Console.WriteLine("ID\tName\t\t\tAge");
foreach (Person p in query1.ToList<Person>())
{
    Console.WriteLine("{0}\t{1}\t\t{2}", p.PersonID, p.Name, p.Age);
}

6、获取平均值、最大值、最小值

// avgerage, max, min age of the persons
double avgAge = (from p in persons
                    select p.Age).Average();
Console.WriteLine("The average age of the persons is {0:f2}", avgAge);

double maxAge = (from p in persons
                    select p.Age).Max();
Console.WriteLine("The Max age of the persons is {0}", maxAge);

double minAge = (from p in persons
                    select p.Age).Min();
Console.WriteLine("The min age of the persons is {0}", minAge);

7、特定条件查询(获取20岁以上的人名)

// Count the persons who age is larger than 20
var query2 = from p in persons
                where p.Age > 20
                select p;

int count = query2.Count();
Console.WriteLine("{0} persons are older than 20:", count);
for (int i = 0; i < count; i++)
{
    Console.WriteLine(query2.ElementAt(i).Name);
}

输出结果：

上述示例，参考了MSDN。