foreach遍历linq所有数据

foreach遍历linq所有数据
linq 能查询的数据

对象。比如集合、数组、字符串等等。
关系。分为 linq to dataset 和 linq to sql，前者用于 dataset 查询，后者用于 sql server 数据库教程查询（相信今后还会支持其他数据库）。
xml。xml 文件、xml 对象等。
linq 优点

不论查什么数据，都是统一的结构。
功能比其他查询方式更强。
可以在编译时进行语法检查，不像 sql 字符串，只能在运行时发现其是否有语法错误。
可以在编译时进行类型检查。
开发时有 intellisense 支持。
调试方便。
linq 环境

linq 要在 .net framework 3.5 下使用，其支持的语言有：c# 3.0、vb9。所以在 windows 2000 下无法使用 linq，因为 windows 2000 下无法安装 .net framework 3.5

using system;
using system.collections.generic;
using system.linq;
using system.text;

public class mainclass {
public static void main() {
list customers = getcustomerlist();
var wacustomers =
from c in customers
where c.region == "r1"
select c;
foreach (var customer in wacustomers) {
console.writeline("customer {0}: {1}", customer.customerid, customer.companyname);
foreach (var order in customer.orders) {
console.writeline(" order {0}: {1}", order.id, order.orderdate);
}
}
}
static list getcustomerlist() {
list emptree = new list();
emptree.add(new product { productname = "a", category = "o", unitprice = 12, unitsinstock = 5, total = 36, orderdate = new datetime(2005, 1, 1), id = 1 });
emptree.add(new product { productname = "b", category = "o", unitprice = 2, unitsinstock = 4, total = 35, orderdate = new datetime(2005, 1, 1), id = 1 });
emptree.add(new product { productname = "c", category = "o", unitprice = 112, unitsinstock = 3, total = 34, orderdate = new datetime(2005, 1, 1), id = 1 });
emptree.add(new product { productname = "d", category = "o", unitprice = 112, unitsinstock = 0, total = 33, orderdate = new datetime(2005, 1, 1), id = 1 });
emptree.add(new product { productname = "e", category = "o", unitprice = 1112, unitsinstock = 2, total = 32, orderdate = new datetime(2005, 1, 1), id = 1 });
emptree.add(new product { productname = "f", category = "o", unitprice = 11112, unitsinstock = 0, total = 31, orderdate = new datetime(2005, 1, 1), id = 1 });

list l = new list();
l.add(new customer { companyname = "a", region = "r1", unitsinstock = 1, orders = emptree, customerid =0});
l.add(new customer { companyname = "b", region = "r2", unitsinstock = 2, orders = emptree, customerid = 1 });
l.add(new customer { companyname = "c", region = "r3", unitsinstock = 3, orders = emptree, customerid = 2 });
l.add(new customer { companyname = "d", region = "r4", unitsinstock = 4, orders = emptree, customerid = 3 });
l.add(new customer { companyname = "e", region = "r5", unitsinstock = 5, orders = emptree, customerid = 4 });
return l;
}
}

class customer : icomparable {
public string companyname { get; set; }
public string region { get; set; }
public list orders { get; set; }
public int unitsinstock { get; set; }
public int customerid { get; set; }

public override string tostring() {
return string.format("id: {0}, name: {1}, region: {3}", this.customerid, this.companyname, this.region);
}
int icomparable.compareto(customer other) {
if (other == null)
return 1;

if (this.customerid > other.customerid)
return 1;

if (this.customerid return -1;

return 0;
}
}
class product : icomparable {
public string productname { get; set; }
public string category { get; set; }
public int unitprice { get; set; }
public int unitsinstock { get; set; }
public int total { get; set; }
public datetime orderdate { get; set; }
public int id { get; set; }

public override string tostring() {
return string.format("id: {0}, name: {1} , category: {3}", this.id, this.productname, this.category);
}
int icomparable.compareto(product other) {
if (other == null)
return 1;
if (this.id > other.id)
return 1;

if (this.id return -1;

return 0;
}
}