orderby 子句 (C# 參考)
在查詢運算式中，orderby 子句可讓傳回的序列或子序列 (群組) 以遞增或遞減順序排序。 您可以指定多個索引鍵，以便執行一或多個次要排序作業。 排序是由項目類型的預設比較子執行。 預設排序順序為遞增。 您也可以指定自訂比較子。 不過，它只有在使用以方法為基礎的語法時才可用。 如需詳細資訊，請參閱排序資料。
範例 1
在下列範例中，第一個查詢會依照從 A 開始的字母順序排序字組，第二個查詢則以遞減順序排序相同的字組 (ascending 關鍵字是預設排序值，而且可以省略)。
class OrderbySample1
{
static void Main()
{
// Create a delicious data source.
string[] fruits = ["cherry", "apple", "blueberry"];
// Query for ascending sort.
IEnumerable<string> sortAscendingQuery =
from fruit in fruits
orderby fruit //"ascending" is default
select fruit;
// Query for descending sort.
IEnumerable<string> sortDescendingQuery =
from w in fruits
orderby w descending
select w;
// Execute the query.
Console.WriteLine("Ascending:");
foreach (string s in sortAscendingQuery)
{
Console.WriteLine(s);
}
// Execute the query.
Console.WriteLine(Environment.NewLine + "Descending:");
foreach (string s in sortDescendingQuery)
{
Console.WriteLine(s);
}
}
}
/* Output:
Ascending:
apple
blueberry
cherry
Descending:
cherry
blueberry
apple
*/
範例 2
下列範例會對學生的姓氏執行主要排序，然後對其名字執行次要排序。
class OrderbySample2
{
// The element type of the data source.
public class Student
{
public required string First { get; init; }
public required string Last { get; init; }
public int ID { get; set; }
}
public static List<Student> GetStudents()
{
// Use a collection initializer to create the data source. Note that each element
// in the list contains an inner sequence of scores.
List<Student> students = new List<Student>
{
new Student {First="Svetlana", Last="Omelchenko", ID=111},
new Student {First="Claire", Last="O'Donnell", ID=112},
new Student {First="Sven", Last="Mortensen", ID=113},
new Student {First="Cesar", Last="Garcia", ID=114},
new Student {First="Debra", Last="Garcia", ID=115}
};
return students;
}
static void Main(string[] args)
{
// Create the data source.
List<Student> students = GetStudents();
// Create the query.
IEnumerable<Student> sortedStudents =
from student in students
orderby student.Last ascending, student.First ascending
select student;
// Execute the query.
Console.WriteLine("sortedStudents:");
foreach (Student student in sortedStudents)
Console.WriteLine(student.Last + " " + student.First);
// Now create groups and sort the groups. The query first sorts the names
// of all students so that they will be in alphabetical order after they are
// grouped. The second orderby sorts the group keys in alpha order.
var sortedGroups =
from student in students
orderby student.Last, student.First
group student by student.Last[0] into newGroup
orderby newGroup.Key
select newGroup;
// Execute the query.
Console.WriteLine(Environment.NewLine + "sortedGroups:");
foreach (var studentGroup in sortedGroups)
{
Console.WriteLine(studentGroup.Key);
foreach (var student in studentGroup)
{
Console.WriteLine(" {0}, {1}", student.Last, student.First);
}
}
}
}
/* Output:
sortedStudents:
Garcia Cesar
Garcia Debra
Mortensen Sven
O'Donnell Claire
Omelchenko Svetlana
sortedGroups:
G
Garcia, Cesar
Garcia, Debra
M
Mortensen, Sven
O
O'Donnell, Claire
Omelchenko, Svetlana
*/
備註
在編譯時期，orderby 子句會轉譯為 OrderBy 方法的呼叫。 orderby 子句中的多個索引鍵翻譯為 ThenBy 方法呼叫。
