'let'关键字在查询语法中很有用。它投影了一个新的范围变量,允许复用使用表达式并使查询更具可读性。
例如,您可以比较字符串值并选择小写字符串值,如下所示:
IList<Student> studentList = new List<Student>() { new Student() { StudentID = 1, StudentName = "John", Age = 18 } , new Student() { StudentID = 2, StudentName = "Steve", Age = 21 } , new Student() { StudentID = 3, StudentName = "Bill", Age = 18 } , new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } , new Student() { StudentID = 5, StudentName = "Ron" , Age = 21 } }; var lowercaseStudentNames = from s in studentList where s.StudentName.ToLower().StartsWith("r") select s.StudentName.ToLower();
正如您看到的,ToLower()方法在上面的查询中被多次使用。下面的示例使用“ let”引入新的变量“ lowercaseStudentName”,然后将在每个地方使用该变量。因此,let关键字使查询更具可读性。
示例:C#中的let关键字
var lowercaseStudentNames = from s in studentList let lowercaseStudentName = s.StudentName.ToLower() where lowercaseStudentName.StartsWith("r") select lowercaseStudentName; foreach (var name in lowercaseStudentNames) Console.WriteLine(name);
Dim lowercaseStudentNames = From s In studentList Let lowercaseStudentName = s.StudentName.ToLower() Where lowercaseStudentName.StartsWith("r") Select lowercaseStudentName;
ram ron