可以使用 LINQ 查询来创建包含多个输入序列的元素的输出序列。
下面的示例演示如何组合两个内存中的数据结构，但组合来自 XML 或 SQL 或数据集源的数据时可应用相同的原则。
假定下面两种类类型：
先声明一个 Student类
class Student
{
public string first { get;set;}
public string last{ get;set;}
public int id { get; set; }
public string street { get; set; }
public string city { get; set; }
public List<int> scores;
}
//Teacher 类
class Teacher
{
public string first { get; set; }
public string last { get; set; }
public int id { get; set; }
public string city { get; set; }
}
在windows 控制台程序的
static void Main(string[] args)
｛
List<Student> students = new List<Student>() {
new Student{first="Svetlana",last="Omelchenko",id=111,street="123 Main street",
city="Seattle",scores=new List<int> {75,84,91,39}},
new Student{first="Sven",last="Mortensen",id=113,street="125 Main Street",
city="Lake City",scores=new List<int>{88,94,65,91}
}
};
List<Teacher> teachers = new List<Teacher>() {
new Teacher {first="Ann", last="Beebe", id=945, city = "Seattle"},
new Teacher {first="Alex", last="Robinson", id=956, city = "Redmond"},
new Teacher {first="Michiyo", last="Sato", id=972, city = "Tacoma"}
};
var peopleInSeattle = (from student in students where student.city == "Seattle" select student.last).Concat(from teacher in teachers where teacher.city == "Seattle" select teacher.last);
Console.WriteLine("The following students and teachers live in Seattle:");
foreach (var person in peopleInSeattle)
{
Console.WriteLine(person);
}
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
｝
/* Output:
The following students and teachers live in Seattle:
Omelchenko
Beebe
*/
将内存中的对象转换为 XML
通过 LINQ 查询，可以轻松地在内存中的数据结构、SQL 数据库、ADO.NET 数据集和 XML 流或文档之间转换数据。
下面的示例将内存中的数据结构中的对象转换为 XML 元素。
class XMLTransform
{
static
void Main()
{
// Create the data source by using a collection initializer.
List<Student> students = new List<Student>()
{
new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores = new List<int>{97, 92, 81, 60}},
new Student {First="Claire", Last="O’Donnell", ID=112, Scores = new List<int>{75, 84, 91, 39}},
new Student {First="Sven", Last="Mortensen", ID=113, Scores = new List<int>{88, 94, 65, 91}},
};
// Create the query.
var studentsToXML = new XElement("Root",
from student in students
let x = String.Format("{0},{1},{2},{3}", student.Scores[0],
student.Scores[1], student.Scores[2], student.Scores[3])
select
new XElement("student",
new XElement("First", student.First),
new XElement("Last", student.Last),
new XElement("Scores", x)
) // end "student"
); // end "Root"
// Execute the query.
Console.WriteLine(studentsToXML);
// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
此代码生成下面的 XML 输出：
other
< Root>
<student>
<First>Svetlana</First>
<Last>Omelchenko</Last>
<Scores>97,92,81,60</Scores>
</student>
<student>
<First>Claire</First>
<Last>O'Donnell</Last>
<Scores>75,84,91,39</Scores>
</student>
<student>
<First>Sven</First>
<Last>Mortensen</Last>
<Scores>88,94,65,91</Scores>
</student>
</Root>
对源元素执行操作
输出序列可能不包含源序列的任何元素或元素属性。
输出可能是通过将源元素用作输入参数计算出的值的序列。
在执行下面这个简单查询时，此查询会输出一个字符串序列，该序列值表示根据 double 类型的元素的源序列进行的计算。
|
注意 |
|
如果查询将转换为某个其他域，则不支持在查询表达式中调用方法。 |
class FormatQuery
{
static
void Main()
{
// Data source.
double[] radii = { 1, 2, 3 };
// Query.
IEnumerable<string> query =
from rad in radii
select String.Format("Area = {0}", (rad * rad) * 3.14);
// Query execution.
foreach (string s in query)
Console.WriteLine(s);
// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
/* Output:
Area = 3.14
Area = 12.56
Area = 28.26
*/
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