/// <summary>
/// 根据一个关键字对查询结果进行分组
/// </summary>
public static void LinqGroupBy()
{
var countries = from r in Formula1.GetChampion()
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()
};
Console.WriteLine("----------------使用查询方法------------------");
foreach (var item in countries)
{
Console.WriteLine(item.Country + "\t" + item.Count);
}
Console.WriteLine("----------------使用扩展方法------------------");
var list = new List <Racer>(Formula1.GetChampion());
var countriesEx = list.GroupBy(r => r.Country).Where(g => g.Count() > 2).OrderByDescending(g => g.Count())
.ThenBy(g => g.Key).Select(g => new { Country = g.Key, Count = g.Count() });
foreach (var item in countriesEx)
{
Console.WriteLine("{0,-10} {1}", item.Country, item.Count);
}
}
/// <summary>
/// 使用扩展方法
/// </summary>
public static void ExtensionMethods()
{
var champions = new List <Racer>(Formula1.GetChampion());
IEnumerable <Racer> championsEnumerable = champions.Where(r => r.Country == "UK").OrderByDescending(r => r.Wins);
foreach (Racer racer in championsEnumerable)
{
Console.WriteLine(string.Format("{0:A}", racer));
}
}
/// <summary>
/// 使用linq查询
/// </summary>
public static void LinqQuery()
{
var query = from r in Formula1.GetChampion()
where r.Country == "UK"
orderby r.Wins descending
select r;
foreach (var racer in query)
{
Console.WriteLine(string.Format("{0:A}", racer));
}
}
/// <summary>
/// 聚合操作符
/// </summary>
public static void LinqCount()
{
var query = from r in Formula1.GetChampion()
let numberYear = r.Years.Count()
where numberYear >= 3
select new
{
Name = r.FirstName + " " + r.LastName,
Times = numberYear
};
foreach (var item in query)
{
Console.WriteLine(item.Name + "次数：" + item.Times);
}
}
/// <summary>
/// 内连接
/// </summary>
public static void LinqJoin()
{
//赛车手
var racers = from r in Formula1.GetChampion()
from y in r.Years
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from t in Formula1.GetContructorChampion()
from y in t.Years
select new { Year = y, Name = t.Name };
Console.WriteLine("----------------内连接------------------");
var racersAndTeams = (from r in racers
join t in teams on r.Year equals t.Year
orderby r.Year descending
select new
{
r.Year,
Champion = r.Name,
Constructor = t.Name
}).Take(10);
foreach (var item in racersAndTeams)
{
Console.WriteLine("{0} {1:-20} {2}", item.Year, item.Champion, item.Constructor);
}
Console.WriteLine("----------------左外连接------------------");
var racersAndTeamsLeft = (from r in racers
join t in teams on r.Year equals t.Year into rt
from t2 in rt.DefaultIfEmpty()
select new
{
Year = r.Year,
Champion = r == null?"空选手":r.Name,
Constructor = t2 == null?"空值":t2.Name
}).Take(10);
foreach (var item in racersAndTeamsLeft)
{
Console.WriteLine("{0} {1:-20} {2}", item.Year, item.Champion, item.Constructor);
}
}
/// <summary>
/// 带嵌套的查询分组
/// </summary>
public static void LinqGroupByNested()
{
var countries = from r in Formula1.GetChampion()
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
};
Console.WriteLine("----------------使用查询方法------------------");
foreach (var item in countries)
{
Console.WriteLine(item.Country + "\t" + item.Count);
foreach (string name in item.Racers)
{
Console.WriteLine(name);
}
}
Console.WriteLine("----------------使用扩展方法------------------");
var list = new List <Racer>(Formula1.GetChampion());
var countriesEx = list.GroupBy(r => r.Country).Where(g => g.Count() > 2).OrderByDescending(g => g.Count())
.ThenBy(g => g.Key).Select(g => new {
Country = g.Key,
Count = g.Count(),
Racers = g.OrderBy(r1 => r1.LastName)
.Select(r1 => (r1.FirstName + " " + r1.LastName))
});
foreach (var item in countriesEx)
{
Console.WriteLine("{0,-10} {1}", item.Country, item.Count);
foreach (string name in item.Racers)
{
Console.WriteLine(name);
}
}
}
/// <summary>
/// 筛选，可以合并多个表达式
/// </summary>
public static void LinqFilter()
{
var champions = from r in Formula1.GetChampion()
where r.Wins > 15 && (r.Country == "Brazil" || r.Country == "Australia")
orderby r.Wins descending
select r;
Console.WriteLine("----------------使用查询方法------------------");
foreach (Racer racer in champions)
{
Console.WriteLine(string.Format("{0:A}", racer));
}
var list = new List <Racer>(Formula1.GetChampion());
var championsEx = list.Where(r => r.Wins > 15 && (r.Country == "Brazil" || r.Country == "Brazil")).OrderByDescending(r => r.Wins);
Console.WriteLine("----------------使用扩展方法------------------");
foreach (Racer racer in championsEx)
{
Console.WriteLine(string.Format("{0:A}", racer));
}
}
/// <summary>
/// 复合的from查询
/// </summary>
public static void LinqManyFrom()
{
var drivers = from r in Formula1.GetChampion()
from c in r.Cars
where c == "Ferrari"
orderby r.LastName
select r.FirstName + " " + r.LastName;
Console.WriteLine("----------------使用查询方法------------------");
foreach (string name in drivers)
{
Console.WriteLine(name);
}
Console.WriteLine("----------------使用扩展方法------------------");
var list = new List <Racer>(Formula1.GetChampion());
IEnumerable <string> names = list.SelectMany(r => r.Cars, (r, c) => new { Racer = r, Car = c }).Where(r => r.Car == "Ferrari").OrderBy(r => r.Racer.LastName).Select(a => a.Racer.FirstName + " " + a.Racer.LastName);
foreach (string name in names)
{
Console.WriteLine(name);
}
}
/// <summary>
/// 集合合并
/// </summary>
public static void LinqZip()
{
var racersName = from r in Formula1.GetChampion()
where r.Country == "Italy"
orderby r.Wins descending
select new
{
Name = r.FirstName + " " + r.LastName
};
var racerNameAndStart = from r in Formula1.GetChampion()
where r.Country == "Italy"
orderby r.Wins descending
select new
{
FirstName = r.FirstName,
Starts = r.Starts
};
var racers = racersName.Zip(racerNameAndStart, (first, second) => first.Name + "Starts:" + second.Starts);
foreach (var name in racers)
{
Console.WriteLine(name);
}
}
