private static IEnumerable <Racer> GetRacersByCar(string car)
{
return(from r in Formulal.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r);
}
private static void LinqQuery()
{
var query = from r in Formulal.GetChampions()
where r.Country == "UK"
orderby r.Wins descending
select r;
foreach (var racer in query)
{
Console.WriteLine($"r:{racer}");
}
}
static void Main(string[] args)
{
//LinqQuery();
//Console.WriteLine("Hello World!");
#region 延迟加载和ToList()
//var names = new List<string> {"Nino", "Alberto", "Juan", "Mike", "Phil"};
//var namesWithJ = (from n in names where n.StartsWith("J") orderby n select n);
//Console.WriteLine("First iteration");
//foreach (string name in namesWithJ)
//{
// Console.WriteLine(name);
//}
//Console.WriteLine();
//names.Add("John");
//names.Add("Jim");
//names.Add("Jack");
//names.Add("Denny");
//Console.WriteLine("Second iteration");
//foreach (var item in namesWithJ)
//{
// Console.WriteLine(item);
//}
#endregion
#region Linq查询操作符
#region Where 筛选
//var racers = from r in Formulal.GetChampions() where r.Wins > 15 &&(r.Country == "USA" || r.Country == "UK") select r;
//var racers2 = Formulal.GetChampions().Where(r => r.Wins > 15 && (r.Country == "USA" || r.Country == "UK")).Select(r=>r);
//foreach (var r in racers2)
//{
// Console.WriteLine($"{r:A}");
//}
#endregion
#region 索引筛选
//查询姓氏以A开头的所有赛车手,并且索引是奇数的赛车手
//var racers3 = Formulal.GetChampions().Where((r, index) => r.LastName.StartsWith("A") && index % 2 != 0);
//foreach (var racer in racers3)
//{
// Console.WriteLine($"{racer:A}");
//}
#endregion
#region 类型筛选
//object[] data = {"one", 1, 3, "four", "five", 6};
//var query = data.OfType<string>();
//Console.WriteLine("输出string类型");
//foreach (var s in query)
//{
// Console.WriteLine(s);
//}
//Console.WriteLine("输出int类型");
//var query2 = data.OfType<int>();
//foreach (var q in query2)
//{
// Console.WriteLine(q);
//}
#endregion
#region 合的from子句
//如果需要根据对象的一个成员进行筛选，而该成员本身是一个系列，就可以使用复合的from子句
//var ferrariDrivers = from r in Formulal.GetChampions()
// from c in r.Cars
// where c == "Ferrari"
// orderby r.LastName
// select r.FirstName + " " + r.LastName;
//foreach (var item in ferrariDrivers)
//{
// Console.WriteLine(item);
//}
//Console.WriteLine("=====SelectMany查询方法======");
//var ferrariDrivers1 = 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+" " +r.Car);
//foreach (var item in ferrariDrivers1)
//{
// Console.WriteLine(item);
//}
#endregion
#region 排序
//var racers = from r in Formulal.GetChampions()
// where r.Country == "Italy"
// orderby r.Wins descending
// select r;
//foreach (var racer in racers)
//{
// Console.WriteLine(racer);
//}
//Console.WriteLine();
//var racers1 = Formulal.GetChampions().Where(r => r.Country == "Italy").OrderByDescending(r => r.Wins);
//foreach (var racer in racers1)
//{
// Console.WriteLine(racer);
//}
//var racers2 =
// (from r in Formulal.GetChampions() orderby r.Country, r.LastName, r.FirstName select r).Take(10);
//foreach (var racer in racers2)
//{
// Console.WriteLine(racer);
//}
//Console.WriteLine();
//var racer3 = Formulal.GetChampions().OrderBy(r => r.Country).ThenBy(r => r.LastName)
// .ThenBy(r => r.FirstName).Take(10);
//foreach (var racer in racer3)
//{
// Console.WriteLine(racer);
//}
#endregion
#region 分组-group子句
//要根据一个关键字值对查询结果分组，可以使用group子句
//一级方程式冠军按照国家分组，并列出一个国家的冠军数。
//根据获得的冠军数降序排列 如果冠军数一样就按照关键字Key来排序 这里的Key=Country
//var countries = from r in Formulal.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(value: $"{item.Country,-10} {item.Count}");
//}
//Console.WriteLine("==============");
//var countries1 = Formulal.GetChampions().GroupBy(r => r.Country).OrderByDescending(g => g.Count()).ThenBy(g => g.Key).Where(g => g.Count() >= 2).Select(g => new { Country = g.Key, Count = g.Count() });
//foreach (var c in countries1)
//{
// Console.WriteLine($"{c.Country,-10}{c.Count}");
//}
#endregion
#region Linq中的变量
//在分组编写的Linq查询中，Count方法调用了多次，使用let子句可以改变这种方式，let允许在linq查询中定义变量
//var countries4 = 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 countries4)
//{
// Console.WriteLine($"{item.Country,-10}{item.Count}");
//}
//Console.WriteLine("=============");
////下面这个第一个Select 是用来创建匿名类型，这里创建了一个Group和Count属性的匿名类型
////带有这些属性的一组传递给OrderByDescending方法，基于匿名属性的Count进行排列
////不过这个要有一个注意点 应考虑根据let或select方法创建的临时对象的数量，查询大列表时，创建的大量对象需要以后进行垃圾收集，这可能对性能产生巨大的影响。
//var countries5 = Formulal.GetChampions().GroupBy(r => r.Country)
// .Select(g => new { Group = g, Count = g.Count() }).OrderByDescending(c => c.Count)
// .ThenBy(g => g.Group.Key).Where(g => g.Count >= 2)
// .Select(g => new { Country = g.Group.Key, Count = g.Count });
//foreach (var item in countries5)
//{
// Console.WriteLine($"{item.Country,-10}{item.Count}");
//}
#endregion
#region 对嵌套的对象分组
//如果分组的对象包含嵌套的序列，就可以改变select子句创建的匿名类型
//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,
// Racers = from r1 in g orderby r1.LastName select r1.FirstName + " " + r1.LastName
// };
//foreach (var item in countries)
//{
// Console.WriteLine($"{item.Country,-10} {item.Count}");
// Console.WriteLine("====车手姓名====");
// foreach (var name in item.Racers)
// {
// Console.WriteLine($"{name}");
// }
//}
#endregion
#region 内连接
////使用 join子句可以根据特定的条件合并两个数据源。
//var racers = from r in Formulal.GetChampions()
// from y in r.Years
// select new
// {
// Year = y,
// Name = r.FirstName + " " + r.LastName
// };
//var teams = from r in Formulal.GetContructorChampions()
// from y in r.Years
// select new
// {
// Year = y,
// Name = r.Name
// };
////通过join子句，根据赛车手获得的冠军的年份和车队活的冠军的年份进行连接。
//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);
//Console.WriteLine("Year World Champion \t Constructor Title");
//foreach (var item in racersAndTeams)
//{
// Console.WriteLine($"{item.Year}:{item.champion,-20} {item.Constructor}");
//}
//Console.WriteLine("==============");
////也可以合并为一个linq查询
//var racersAndTeams1 = (from r in from r1 in Formulal.GetChampions()
// from y1 in r1.Years
// select new
// {
// Year=y1,
// Name=r1.FirstName +" "+r1.LastName
// } join t in from t1 in Formulal.GetContructorChampions() from y1 in t1.Years select new
//{
// Year=y1,
// Name=t1.Name
//} on r.Year equals t.Year orderby t.Year select new
//{
// Year=r.Year,
// Racer=r.Name,
// Team=t.Name
//}).Take(10);
#endregion
#region 左外连接
//左外连接返回左边序列中的全部元素，即使它们在右边的序列中并没有匹配的元素
//和sql 的左连接一样
var racers = from r in Formulal.GetChampions()
from y in r.Years
select new
{
Year = y,
Name = r.FirstName + " " + r.LastName
};
var teams = from r in Formulal.GetContructorChampions()
from y in r.Years
select new
{
Year = y,
Name = r.Name
};
//使用左外连接 用join 子句和DefalutIfEmpty方法定义 如果查询的左侧没有匹配的车队冠军，那么就使用DefaultIfEmpty方法定义其右侧的默认值
//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);
//foreach (var item in racersAndTeams)
//{
// Console.WriteLine(item);
//}
#endregion
#region 组连接
//var racers2 = Formulal.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 Formulal.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($"{r.FirstName} {r.LastName}");
// foreach (var item in r.Results)
// {
// Console.WriteLine($"{item.Year} {item.Position}");
// }
//}
#endregion
#region 集合操作
//var ferrriDrivers = from r in Formulal.GetChampions()
// from c in r.Cars
// where c == "Ferrari"
// orderby r.LastName
// select r;
//Console.WriteLine("World Champion with ferrari and Mclaren");
//foreach (var racer in racerByCar("Ferrari").Intersect(racerByCar("Mclaren")))
//{
// Console.WriteLine(racer);
//}
#endregion
#region 合并操作
//合并是对两个相关序列合并为一个， 第一个集合中的第一项与第二个集合中的第一项合并，第一个集合中的第二项会与第二个集合中的第二项合并。依此类推，如果两个序列的项数不同。Zip()方法就在达到最小集合的末尾时停止。
//var racerNames = from r in Formulal.GetChampions()
// where r.Country == "Italy"
// orderby r.Wins descending
// select new
// {
// Name = r.FirstName + " " + r.LastName
// };
//var racerNamesAndStarts = from r in Formulal.GetChampions()
// where r.Country == "Italy"
// orderby r.Wins descending
// select new
// {
// LastName = r.LastName,
// Starts = r.Starts
// };
//var racers5 = racerNames.Zip(racerNamesAndStarts,
// (first, second) => first.Name + ",Starts:" + second.Starts);
//foreach (var item in racers5)
//{
// Console.WriteLine(item);
//}
//int[] numbers = { 1, 2, 3, 4 };
//string[] words = { "one", "two", "three" };
//var numbersAndWords = numbers.Zip(words, (first, second) => first + " " + second);
//foreach (var item in numbersAndWords)
// Console.WriteLine(item);
#endregion
#region 分区/分页
//int pageSize = 5;
//int numberPages = (int) Math.Ceiling(Formulal.GetChampions().Count() / (double) pageSize);
//for (int i = 0; i < numberPages; i++)
//{
// Console.WriteLine($"Page :{i}");
// var racers6 = (from r in Formulal.GetChampions()
// orderby r.LastName, r.FirstName
// select r.FirstName + " " + r.LastName).Skip(i * pageSize).Take(numberPages);
// foreach (var item in racers6)
// {
// Console.WriteLine(item);
// }
//}
// string[] fruits = { "apple", "banana", "mango", "orange",
// "passionfruit", "grape" };
// IEnumerable<string> query =
// fruits.SkipWhile(fruit => String.Compare("orange", fruit,
//StringComparison.OrdinalIgnoreCase) != 0);
// foreach (string fruit in query)
// {
// Console.WriteLine(fruit);
// }
#endregion
#region 聚合操作符
//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($"{r.Name} {r.timesChampion}");
//}
#endregion
#region 转换操作符
//var racers7 = (from r in Formulal.GetChampions()
// from c in r.Cars
// select new
// {
// Car = c, Racer = r
// }).ToLookup(cr => cr.Car, cr => cr.Racer);
//if (racers7.Contains("Ferrari"))
//{
// foreach (var racer in racers7["Ferrari"])
// {
// Console.WriteLine(racer);
// }
//}
//var list = new ArrayList(Formulal.GetChampions() as ICollection ?? throw new InvalidOperationException());
//var query = from r in list.Cast<Racer>() where r.Country == "USA" select r;
//foreach (var racer in query)
//{
// Console.WriteLine($"{racer:A}",racer);
//}
#endregion
#region 生成操作符
var values = Enumerable.Range(1, 20);
foreach (var item in values)
{
Console.WriteLine($"{item}", item);
}
#endregion
#endregion
Console.ReadKey();
}
