LinqToSql--预备知识

1.隐含类型局部变量

例子:

    protected void Page_Load(object sender, EventArgs e)
    {
        var str = "this is a string";
        Display(str.GetType());

        var integer = 100;
        Display(integer.GetType());

        var array = new int[] { 1, 2, 3, 4, 5 };
        Display(array.GetType());

        var DefineArray = new DefineClass[] { new DefineClass(), new DefineClass(), new DefineClass() };
        Display(DefineArray.GetType());

    }

var只能用于局部变量,而不能用于字段.

2.匿名类型

允许开发人员定义行内类型,无虚显示定义类型,常与var配合使用,var用于声明匿名类型

例子:

    protected void Page_Load(object sender, EventArgs e)
    {
        var user = new { name = "www", password = "111" };
        Response.Write(user.name+"<br/>");
        Response.Write(user.password + "<br/>");
        Response.Write(user.GetType().ToString() + "<br/>");

    }

结果:

3.扩展方法

static class DefineClassHelper
{
    public static string GetTypeString(this DefineClass dc)
    {
        return dc.GetType().ToString();
    }
}

class DefineClass
{
}

public partial class linq_Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        DefineClass dc = new DefineClass();
        Response.Write(dc.GetTypeString());

    }
}

DefineClass并没有定义GetTypeString方法,但是,定义了一个DefineClass的静态类,为该类提供了一个方法.

4.自动属性

例子:

class DefineClass
{
    public string name
    {
        get;
        set;
    }

    public int age
    {
        get;
        private set;
    }
}

对于上例的age属性,只能获取,而不能再类的外部对该属性进行赋值.

5.对象初始化器

例子:

public class Person
{
    public string name;
    public string password;
}

对于这个类,可以使用如下方法进行初始化:

    protected void Page_Load(object sender, EventArgs e)
    {
        Person p = new Person() { name = "www", password = "111" };
    }

也可以进行如下初始化:

Person p = new Person { name = "www", password = "111" };

即:去掉括号也可以.

但是如果类定义如下,则不能进行这样的初始化:

public class Person
{
    public string name;
    public string password;

    public Person(string name,string password)
    {
        this.name = name;
        this.password = password;
    }
}

即:该类并没有默认的构造函数时,会报错.

6.集合初始化器

例子:

public partial class linq_Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        IList<Person> list = new List<Person>{
            new Person(){name="www",password="111"},
            new Person(){name="zzz",password="222"}
        };

        foreach (Person p in list)
        {
            Response.Write(p.ToString());
        }

    }
}

public class Person
{
    public string name;
    public string password;

    public override string ToString()
    {
        return this.name+"--"+this.password+"<br/>";
    }
}

结果:

7.Lambda表达式

例子:

    protected void Page_Load(object sender, EventArgs e)
    {
        int[]  arr = new int[] { 1, 2, 3, 4, 5, 6, 6, 7, 8, 9 };

        var result = from a in arr
                     select a;

        foreach (var r in result)
        {
            Response.Write(r.ToString()+"<br/>");
        }
    }

效果: