private static void Math()
{
var query = from r in Formula1.GetChampions()
let numberYears = r.Years.Count()
where numberYears >= 3
orderby numberYears descending, r.LastName
select new
{
Name = r.FirstName + " " + r.LastName,
TimesChampion = numberYears
};
foreach (var r in query)
{
Console.WriteLine("{0} {1}", r.Name, r.TimesChampion);
}
var countrys = (from c in
from r in Formula1.GetChampions()
group r by r.Country into c
select new
{
Country = c.Key,
Wins = (from r1 in c select r1.Wins).Sum()
}
orderby c.Wins descending, c.Country
select c).Take(10);
foreach (var country in countrys)
{
Console.WriteLine("{0} {1}", country.Country, country.Wins);
}
}
//在非类型化的集合上使用linq查询 需要cast
private static void Cast()
{
var lists = new System.Collections.ArrayList(Formula1.GetChampions() as System.Collections.ICollection);
var quary = from r in lists.Cast <Racer>()
where r.Country == "USA"
orderby r.Wins descending
select r;
foreach (var racer in quary)
{
Console.WriteLine("{0:A}", racer);
}
}
private static void MoreFrom()
{
//多个from的写法 转换为（SelectMany）的重载版本
var ferrariDrivers = from r in Formula1.GetChampions()
from c in r.Cars
where c == "Ferrari"
orderby r.LastName
select r.FirstName + " " + r.LastName;
foreach (string s in ferrariDrivers)
{
Console.WriteLine(s);
}
}
private static void delegateSelect()
{
//定义一个委托方法保存查询
Func <string, IEnumerable <Racer> > racersByCar = car =>
from r in Formula1.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r;
//查询同时满足这两个条件的集合
foreach (var racer in racersByCar("Ferrari").Intersect(racersByCar("McLaren")))
{
Console.WriteLine(racer);
}
}
//分页
private static void PageSize()
{
int pageSize = 5;
int numberPages = (int)Math.Ceiling(Formula1.GetChampions().Count() / (double)pageSize);
for (int page = 0; page < numberPages; ++page)
{
var racers = (from r in Formula1.GetChampions()
orderby r.LastName, r.FirstName
select r.FirstName + " " + r.LastName).Skip(page * pageSize).Take(pageSize);
foreach (var name in racers)
{
Console.WriteLine(name);
}
Console.WriteLine();
}
}
private static void Join()
{
var racers = from r in Formula1.GetChampions()
from y in r.Years
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from t in Formula1.GetContructorChampions()
from y in t.Years
select new
{
Year = y,
Name = t.Name
};
var racersAndTeams = (from r in racers
join t in teams on r.Year equals t.Year
select new
{
r.Year,
Champion = r.Name,
Constructor = t.Name
}).Take(10); //取前10项
//左外连接 teams 项可能为空值
var racersWithTeams = (from r in racers
join t in teams on r.Year equals t.Year into rt
from t in rt.DefaultIfEmpty()
orderby r.Year
select new
{
Year = r.Year,
Champion = r.Name,
Constructor = t == null ? "no constructor championship" : t.Name
}).Take(10);
Console.WriteLine("Year World Champion \t Constructor Title");
foreach (var item in racersAndTeams)
{
Console.WriteLine("{0}: {1, -20} {2}", item.Year, item.Champion, item.Constructor);
}
foreach (var item in racersWithTeams)
{
Console.WriteLine("{0}: {1, -20} {2}", item.Year, item.Champion, item.Constructor);
}
}
private static void ToLookup()
{
var racers = (from r in Formula1.GetChampions()
from c in r.Cars
select new
{
Car = c,
Racer = r
}).ToLookup(cr => cr.Car, cr => cr.Racer);
if (racers.Contains("Williams"))
{
foreach (var williamsRacer in racers["Williams"])
{
Console.WriteLine(williamsRacer);
}
}
}
private static void Zip()
{
var racerName = from r in Formula1.GetChampions()
where r.Country == "Italy"
orderby r.Wins descending
select new { Name = r.FirstName + " " + r.LastName };
var racerNamesAndStarts = from r in Formula1.GetChampions()
where r.Country == "Italy"
orderby r.Wins descending
select new { LastName = r.LastName, Starts = r.Starts };
//此处将两次查询合并
var racers = racerName.Zip(racerNamesAndStarts, (first, second) => first.Name + " , starts: " + second.Starts);
foreach (var r in racers)
{
Console.WriteLine(r);
}
}
//要使用Linq 其容器必须实现IEnumerable<ISource> 接口
private static void LinqQuery()
{
//创建linq的查询语句
var query = from r in Formula1.GetChampions() where r.Country == "UK" orderby r.Wins descending select r; //where中可包含逻辑运算符
/* 上面的linq语句 相当于下面的函数调用 */
//IEnumerable<Racer> ukChampions = Formula1.GetChampions().Where(r => r.Country == "UK")
// .OrderByDescending(r => r.Wins).Select(r => r);
foreach (Racer r in query)
{
Console.WriteLine("{0:A}", r);
}
/*
* 查询语句必须以from开头，elect 或 group 结尾，中间可以用 where orderby join let 等
*/
}
private static void Group()
{
var countries = from r in Formula1.GetChampions()
group r by r.Country into g
orderby g.Count() descending, g.Key
where g.Count() >= 2
select new {
Country = g.Key,
Count = g.Count(),
//这里嵌套一个查询
Racers = from r1 in g
orderby r1.LastName
select r1.FirstName + " " + r1.LastName
};
foreach (var item in countries)
{
Console.WriteLine("{0, -10} {1}", item.Country, item.Count);
}
}
