如何理解这个lambda表达式？

Question

我是C#新手.有人可以帮我理解这个C#lambda表达式吗？

var projs = allCustomers.SelectMany(osd => osd.phoneNumbers,
                                   (osd, osv) => new { customer= osd, phoneNumber= osv });

谢谢/下摆

Answer 1

您正在使用此重载的SelectMany.

public static IEnumerable<TResult> SelectMany<TSource, TCollection, TResult>(
      this IEnumerable<TSource> source,
      Func<TSource, IEnumerable<TCollection>> collectionSelector,
      Func<TSource, TCollection, TResult> resultSelector
)

有三个参数:

source :
Type: System.Collections.Generic.IEnumerable<TSource>
A sequence of values to project.

collectionSelector
Type: System.Func<TSource, IEnumerable<TCollection>>
A transform function to apply to each element of the input sequence.

resultSelector
Type: System.Func<TSource, TCollection, TResult>
A transform function to apply to each element of the intermediate sequence.

在你的情况下,source是allCustomers,collectionSelector是表达式:

osd => osd.phoneNumber 

而且resultSelector是:

(osd, osv) => new { customer= osd, phoneNumber= osv }

这里第一个表达式表示取每个customer并返回它phoneNumbers.在第二个表达式中,osdis customer,osvis 的类型phoneNumber和结果是​​匿名类型.它接受每个客户和电话号码并使用这些值创建匿名类型.

以下是此查询的作用示例:

Customer - Phone Numbers
------------------------
John      1234567,2331212,1122334
Jack      1456771,9485323
Juliet    2401232

结果将是:

John   1234567
John   2331212
John   1122334
Jack   1456771
Jack   9485323
Juliet 2401232