static void GroupJoin()
{
// var q =
//from c in categories
//join p in products on c equals p.Category into ps
//select new { Category = c, Products = ps };
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 into ts
select new
{
Year = r.Year,
Racer = r.Name,
Constructor = ts
};
foreach (var r in racersAndTeams)
{
Console.WriteLine("{0} {1}", r.Year, r.Racer);
foreach (var t in r.Constructor)
{
Console.WriteLine("\t{0}", t.Name);
}
}
}
static void LeftOuterJoin()
{
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 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 Champion\t\t Constructor Title");
foreach (var item in racersAndTeams)
{
Console.WriteLine("{0}: {1,-20} {2}",
item.Year, item.Champion, item.Constructor);
}
}
static void InnerJoin()
{
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
orderby t.Year
select new
{
Year = r.Year,
Champion = r.Name,
Constructor = 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);
}
}
// 4.操作符实例
static void OpteratorSampleMethod()
{
// 1.使用where子句，可以合并多个表达式
var racers = from r in Formula1.GetChampions()
where r.Wins > 15 && (r.Country == "Brazil" || r.Country == "Austria")
select r;
DisplayRacers(racers);
// 2.使用索引查询
racers = Formula1.GetChampions().
Where((r, index) => r.LastName.StartsWith("A") && index % 2 != 0);
DisplayRacers(racers);
// 3.类型筛选
Console.WriteLine("类型筛选");
object[] data = { "one", 2, 3, "four", "five", 6 };
var query = data.OfType <string>();
foreach (var s in query)
{
Console.WriteLine(s);
}
Console.WriteLine();
// 4.复合的from子句
Console.WriteLine("复合的from子句");
var ferrariDrivers = from r in Formula1.GetChampions()
from c in r.Cars
where c == "Ferrari"
orderby r.LastName
select r.FirstName + " " + r.LastName;
DisplayRacers(ferrariDrivers);
// 5.排序
Console.WriteLine("排序");
racers = (from r in Formula1.GetChampions()
orderby r.Country, r.LastName, r.FirstName
select r).Take(10);
DisplayRacers(racers);
// 6.分组
Console.WriteLine("分组");
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()
};
foreach (var item in countries)
{
Console.WriteLine("{0,-10} {1}", item.Country, item.Count);
}
Console.WriteLine();
// 7.对嵌套的对象分组
Console.WriteLine("对嵌套内的对象分组");
var mcountries = 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(),
Racers = from r1 in g
orderby r1.LastName
select r1.FirstName + " " + r1.LastName
};
foreach (var item in mcountries)
{
Console.WriteLine("{0,-10} {1}", item.Country, item.Count);
foreach (var name in item.Racers)
{
Console.WriteLine("{0}: ", name);
}
Console.WriteLine();
}
// 8.内连接：使用join子句可以根据特定的条件合并两个数据源，但之前要获得两个连接的列表
var racers1 = 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 racers1
join t in teams on r.Year equals t.Year
select new
{
r.Year,
Champion = r.Name,
Constructor = t.Name
};
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);
}
Console.WriteLine();
// 9.组连接
Console.WriteLine("组连接");
var racers2 = Formula1.GetChampionships()
.SelectMany(cs => new List <RacerInfo>()
{
new RacerInfo
{
Year = cs.Year,
Position = 1,
FirstName = cs.First.FirstName(),
LastName = cs.First.LastName()
},
new RacerInfo
{
Year = cs.Year,
Position = 2,
FirstName = cs.Second.FirstName(),
LastName = cs.Second.LastName()
},
new RacerInfo
{
Year = cs.Year,
Position = 3,
FirstName = cs.Third.FirstName(),
LastName = cs.Third.LastName()
}
});
var q = (from r in Formula1.GetChampions()
join r2 in racers2 on
new
{
FirstName = r.FirstName,
LastName = r.LastName
}
equals
new
{
FirstName = r2.FirstName,
LastName = r2.LastName
}
into yearResults
select new
{
FirstName = r.FirstName,
LastName = r.LastName,
Wins = r.Wins,
Starts = r.Starts,
Results = yearResults
});
foreach (var r in q)
{
Console.WriteLine("{0} {1}", r.FirstName, r.LastName);
foreach (var results in r.Results)
{
Console.WriteLine("{0} {1}", results.Year, results.Position);
}
}
// 10.集合操作
// 定义委托
Console.WriteLine("集合操作");
Func <string, IEnumerable <Racer> > racerByCar = car => from r in Formula1.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r;
Console.WriteLine("World champion with ferrati and McLaren");
foreach (var racer in racerByCar("Ferrari").Intersect(racerByCar("McLaren")))
{
Console.WriteLine(racer);
}
// 11.合并
Console.WriteLine("合并操作");
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
};
var racers3 = racerName.Zip(racerNamesAndStarts, (first, second) => first.Name + ", starts" + second);
foreach (var r in racers)
{
Console.WriteLine(r);
}
Console.WriteLine();
}
