//左外联接
public static void LeftOutJoinRun()
{
var racers = from r in Formulal.GetChampions()
from y in r.Years
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from t in Formulal.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 into rt
from t in rt.DefaultIfEmpty()
orderby r.Year
select new
{
r.Year,
Champion = r.Name,
Constructor = t == null ? "no constructor" : t.Name
}).Take(10);
Console.WriteLine("输出结果：");
foreach (var item in racersAndTeams)
{
Console.WriteLine($"{item.Year}:{item.Champion,-10} {item.Constructor}");
}
}
//分组
public static void GroupRun()
{
var countries = from r in Formulal.GetChampions()
group r by r.Country into g //将分组信息放入标识符g中
orderby g.Count() descending, g.Key
where g.Count() >= 2
select new
{
Country = g.Key,
Count = g.Count()
};
foreach (var item in countries)
{
Console.WriteLine($"{item.Country,-10} {item.Count}");
}
Console.WriteLine();
Console.WriteLine("使用LINQ扩展方法:");
var countries2 = Formulal.GetChampions()
.GroupBy(r => r.Country)
.OrderByDescending(g => g.Count())
.ThenBy(g => g.Key)
.Where(g => g.Count() >= 2)
.Select(g => new { Country = g.Key, Count = g.Count() });
foreach (var item in countries2)
{
Console.WriteLine($"{item.Country,-10} {item.Count}");
}
}
//合并
public static void ZipRun()
{
var racernames = from r in Formulal.GetChampions()
where r.Country == "Italy"
orderby r.Wins descending
select new
{
Name = r.FirstName + " " + r.LastName
};
var racerNamesAndStarts = from r in Formulal.GetChampions()
where r.Country == "Italy"
orderby r.Wins descending
select new
{
LastName = r.LastName,
Starts = r.Starts
};
//第一个集合中的第一项会与第二个集合中的第一项合并
//第一个集合中的第二项会与第二个集合中的第二项合并，依次类推
//如果两个序列的项数不同，Zip()方法就在到达较小集合的末尾时停止
var racers = racernames.Zip(racerNamesAndStarts
, (first, second) => first.Name + ", starts: " + second.Starts);
foreach (var r in racers)
{
Console.WriteLine(r);
}
}
//对嵌套的对象分组
public static void NestingGroupRun()
{
var countries = from r in Formulal.GetChampions()
group r by r.Country into g
let count = g.Count()
orderby count descending, g.Key
where count >= 2
select new
{
Country = g.Key,
Count = count,
//使用内部子句嵌套
Racers = from r1 in g
orderby r1.LastName
select r1.FirstName + " " + r1.LastName
};
foreach (var item in countries)
{
Console.WriteLine($"{item.Country,-10} {item.Count}");
foreach (var name in item.Racers)
{
Console.Write(name + ";");
}
Console.WriteLine();
}
}
//where 条件筛选
public static void WhereRun()
{
var racrers = from r in Formulal.GetChampions()
where r.Wins > 15 && (r.Country == "China" || r.Country == "UK")
select r;
foreach (var r in racrers)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine("使用LINQ扩展方法:");
var racres2 = Formulal.GetChampions()
.Where(r => r.Wins > 15 && (r.Country == "China" || r.Country == "UK"))
.Select(r => r);
foreach (var r in racres2)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine("使用Where索引方法：");
//使用索引筛选，只能使用扩展方法，不能使用Linq查询语句
var racers3 = Formulal.GetChampions()
.Where((r, index) => r.LastName.StartsWith("A") && index % 2 != 0);
foreach (var r in racers3)
{
Console.WriteLine($"{r:A}");
}
}
private static IEnumerable <Racer> GetRacersByCar(string car)
{
var ferrariDrivers = from r in Formulal.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r;
return(ferrariDrivers);
}
static void ExtensionMethods()
{
var champions = new List <Racer>(Formulal.GetChampions());
IEnumerable <Racer> brazilChampions = champions.Where(r => r.Country == "China")
.OrderByDescending(r => r.Wins)
.Select(r => r);
foreach (Racer r in brazilChampions)
{
Console.WriteLine($"{r:A}");
}
}
//转换操作符:ToList
public static void ToListRun()
{
List <Racer> racers = (from r in Formulal.GetChampions()
where r.Starts > 150
orderby r.Starts descending
select r).ToList();
foreach (var racer in racers)
{
Console.WriteLine($"{racer} {racer:S}");
}
}
//排序
public static void OrderByRun()
{
var racers = from r in Formulal.GetChampions()
where r.Country == "China"
orderby r.Wins descending, r.Country ascending
select r;
foreach (var r in racers)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine();
Console.WriteLine("使用LINQ扩展方法:");
var racers2 = Formulal.GetChampions()
.Where(r => r.Country == "China")
.OrderByDescending(r => r.Wins)
.Select(r => r);
foreach (var r in racers2)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine();
Console.WriteLine("=======================");
//多个排序
var racers3 = (from r in Formulal.GetChampions()
orderby r.Country, r.LastName, r.FirstName ascending
select r).Take(10);
foreach (var r in racers3)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine();
Console.WriteLine("使用LINQ扩展方法:");
var racers4 = Formulal.GetChampions()
.OrderBy(r => r.Country)
.ThenBy(r => r.LastName)
.ThenByDescending(r => r.FirstName)
.Take(10);
foreach (var r in racers4)
{
Console.WriteLine($"{r:A}");
}
}
//转换操作符:Cast
public static void CastRun()
{
var list = new System.Collections.ArrayList(Formulal.GetChampions()
as System.Collections.ICollection);
var query = from r in list.Cast <Racer>()
where r.Country == "China"
orderby r.Wins descending
select r;
foreach (var r in query)
{
Console.WriteLine($"{r:A}");
}
}
public static void Run()
{
var query = from r in Formulal.GetChampions()
where r.Country == "China"
orderby r.Wins descending
select r;
foreach (Racer r in query)
{
Console.WriteLine($"{r:A}");
}
Console.WriteLine();
ExtensionMethods();
}
//集合操作
public static void CollectionsRun()
{
Func <string, IEnumerable <Racer> > racersByCar =
car => from r in Formulal.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r;
Console.WriteLine("调用Intersect()方法，显示结果：");
foreach (var racer in racersByCar("Ferrari").Intersect(racersByCar("Lotus")))
{
Console.WriteLine(racer);
}
}
//转换操作符:ToLookup
public static void ToLookupRun()
{
var racers = (from r in Formulal.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 winll in racers["Williams"])
{
Console.WriteLine(winll);
}
}
}
//分区
public static void TakeAndSkipRun()
{
int pageSize = 5;
int numberPages = (int)Math.Ceiling(Formulal.GetChampions().Count() / (double)pageSize);
for (int page = 0; page < numberPages; page++)
{
Console.WriteLine("Page " + page);
var racers = (from r in Formulal.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();
}
}
//复合的from子句
public static void FromRun()
{
//Formulal.GetChampions()返回Racer集合，每一个Racer的属性Cars是一个字符串数组
var ferrariDrivers = from r in Formulal.GetChampions()
from c in r.Cars
where c == "Ferrari"
orderby r.LastName
select r.FirstName + " " + r.LastName;
foreach (string f in ferrariDrivers)
{
Console.WriteLine(f);
}
Console.WriteLine("使用LINQ扩展方法:");
var ferrariDrivers2 = Formulal.GetChampions()
.SelectMany(r => r.Cars, (r, c) => new { Racer = r, Car = c })
.Where(r => r.Car == "Ferrari")
.OrderBy(r => r.Racer.LastName)
.Select(r => r.Racer.FirstName + " " + r.Racer.LastName);
}
//LINQ查询中的变量
public static void LetRun()
{
var countries = from r in Formulal.GetChampions()
group r by r.Country into g
let count = g.Count()
orderby count descending, g.Key
where count >= 2
select new
{
Country = g.Key,
Count = count
};
foreach (var item in countries)
{
Console.WriteLine($"{item.Country,-10} {item.Count}");
}
Console.WriteLine();
Console.WriteLine("使用LINQ扩展方法:");
var countries2 = Formulal.GetChampions()
.GroupBy(r => r.Country)
.Select(g => new { Group = g, Count = g.Count() })
.OrderByDescending(g => g.Count)
.ThenBy(g => g.Group.Key)
.Where(g => g.Count >= 2)
.Select(g => new
{
Country = g.Group.Key,
Count = g.Count
});
foreach (var item in countries2)
{
Console.WriteLine($"{item.Country,-10} {item.Count}");
}
}
//聚合操作费
public static void JuheRun()
{
Console.WriteLine("Count():");
var query = from r in Formulal.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(r.Name + " " + r.TimesChampion);
}
Console.WriteLine();
Console.WriteLine("Sum():");
var countries = (from c in from r in Formulal.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(5);
foreach (var country in countries)
{
Console.WriteLine(country.Country + " " + country.Wins);
}
}
//组联接
public static void ZuJoinRun()
{
var racers = Formulal.GetChampionships()
.SelectMany(cs => new List <RacerInfo>()
{
new RacerInfo
{
Year = cs.Year,
Positon = 1,
FirstName = cs.First.FirstName(),
LastName = cs.First.LastName()
},
new RacerInfo
{
Year = cs.Year,
Positon = 2,
FirstName = cs.Second.FirstName(),
LastName = cs.Second.LastName()
},
new RacerInfo
{
Year = cs.Year,
Positon = 3,
FirstName = cs.Third.FirstName(),
LastName = cs.Third.LastName()
}
});
foreach (var r in racers)
{
Console.WriteLine(r.FirstName + " " + r.LastName);
}
Console.WriteLine();
Console.WriteLine("Linq查询：");
var q = (from r in Formulal.GetChampions()
join r2 in racers on
new
{
FirstName = r.FirstName,
LastName = r.LastName
}
equals
new
{
r2.FirstName,
r2.LastName
}
into yearResults
select new
{
r.FirstName,
r.LastName,
r.Wins,
r.Starts,
Results = yearResults
});
foreach (var r in q)
{
Console.WriteLine(r.FirstName + " " + r.LastName);
foreach (var results in r.Results)
{
Console.WriteLine(results.Year + " " + results.Positon);
}
}
}
//内连接
public static void InnerJoinRun()
{
var racers = from r in Formulal.GetChampions()
from y in r.Years
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from t in Formulal.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
orderby t.Year
select new
{
r.Year,
Champion = r.Name,
Constructor = t.Name
}).Take(10);
Console.WriteLine("输出结果：");
foreach (var item in racersAndTeams)
{
Console.WriteLine($"{item.Year}:{item.Champion,-20} {item.Constructor}");
}
Console.WriteLine();
Console.WriteLine(" 将上述合并为一个LINQ查询:");
var racersAndTeams2 =
(from r in from r1 in Formulal.GetChampions()
from yr in r1.Years
select new
{
Year = yr,
Name = r1.FirstName + " " + r1.LastName
}
join t in
from t1 in Formulal.GetContructorChampions()
from yt in t1.Years
select new
{
Year = yt,
Name = t1.Name
}
on r.Year equals t.Year
orderby t.Year
select new
{
Year = r.Year,
Champion = r.Name,
Constructor = t.Name
}).Take(10);
Console.WriteLine("输出结果：");
foreach (var item in racersAndTeams2)
{
Console.WriteLine($"{item.Year}:{item.Champion,-20} {item.Constructor}");
}
}