LINQ是一种集成在计算机语言里的信息查询语句，是c#3.0中最惹人瞩目的功能。
在C#中，LINQ语句有两种写法。
第一种写法与SQL语句类似：
IEnumerable<Customer> result = from customer in customers
where customer.FirstName == "Donna“
select customer;
第二种写法更加接近c#语句:
IEnumerable<Customer> result =
customers.Where(customer => customer.FirstName == "Donna")
.Select(customer => customer);
这种写法易于理解，所以我认为这种写法更加好。
在Where和Select后面填入的是Lamda语句，这种语句是Delegate的简化，有利于提升代码的阅读性。
Lamda表达式的形式通常是这样的
people=>people.age>30
第一个people指的是传入的参数， =>是Lamda表达式的特定符号，右边是一个表达式，在查询语句中，此符号后面的表达式返回值通常是布尔类型的。例如上面这条语句放在Where中可以筛选出年龄大于三十的人。
下面是一个简单的LINQ和Lambda表达式的运用
customer类：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks; namespace ConsoleApplication3
{
public class Customer
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string HomeAddress { get; set; }
//now override the ToString function of Object class.
public override string ToString()
{
return string.Format("{0} {1}\n Enmail:{2}", FirstName, LastName, HomeAddress);
}
public static List<Customer> CreateCustomerList()
{
List<Customer> customers = new List<Customer>
{
new Customer { FirstName = "Orlando",LastName = "Gee", HomeAddress = "orlando0@adventure-works.com"},
new Customer { FirstName = "Keith", LastName = "Harris",HomeAddress = "keith0@adventure-works.com" },
new Customer { FirstName = "Donna", LastName = "Carreras",HomeAddress = "donna0@adventure-works.com" },
new Customer { FirstName = "Janet", LastName = "Gates",HomeAddress = "janet1@adventure-works.com" },
new Customer { FirstName = "Lucy", LastName = "Harrington",HomeAddress = "lucy0@adventure-works.com" }
};
return customers;
}
}
}
在main函数中查询以D开头的记录
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks; namespace ConsoleApplication3
{
class Program
{
public static void Main()
{
List<Customer> customers = Customer.CreateCustomerList();
IEnumerable<Customer> result =
customers.Where(customer => customer.FirstName.StartsWith("D"));
foreach (Customer customer in result)
{
Console.WriteLine(customer.ToString());
}
}
}
}
关于Xml我用上一个数据库简单的创建了一个xml文档
public static void Main()
{
List<Customer> customers = Customer.CreateCustomerList();
XmlDocument customerXml = new XmlDocument();
XmlElement rootElem = customerXml.CreateElement("customers");
customerXml.AppendChild(rootElem);
foreach (Customer cust in customers) {
XmlElement customerElm = customerXml.CreateElement("customer"); XmlElement firstElm = customerXml.CreateElement("firstName");
firstElm.InnerText = cust.FirstName;
customerXml.AppendChild(firstElm); XmlElement second = customerXml.CreateElement("lastName");
second.InnerText = cust.LastName;
customerXml.AppendChild(second); XmlElement third = customerXml.CreateElement("emailAddress");
third.InnerText = cust.Address;
customerXml.AppendChild(third); rootElem.AppendChild(customerElm);
}
Console.WriteLine(customerXml.OuterXml);
}
运行结果是这样的
<customers>
<customer>
<firstName>Orlando</firstName>
<lastName>Gee</lastName>
<emailAddress>orlando0@adventure-works.com</emailAddress></customer>
<customer>
<firstName>Keith</firstName>
<lastName>Harris</lastName>
<emailAddress>keith0@adventure-works.com</emailAddress></customer>
<customer>
<firstName>Donna</firstName>
<lastName>Carreras</lastName>
<emailAddress>donna0@adventure-works.com</emailAddress>
</customer>
<customer>
<firstName>Janet</firstName>
<lastName>Gates</lastName>
<emailAddress>janet1@adventure-works.com</emailAddress></customer>
<customer>
<firstName>Lucy</firstName>
<lastName>Harrington</lastName>
<emailAddress>lucy0@adventure-works.com</emailAddress></customer></customers>
这里的XmlElement firstElm = customerXml.CreateElement("firstName");语句是定义firstElm标签，这在html中是不行的
而xml的产生需要用到System.Xml.linq;命名空间。