Select 和 SelectMany 的区别

问题描述

我一直在寻找 Select 和 SelectMany 之间的区别，但一直找不到合适的答案.我需要了解使用 LINQ To SQL 时的区别，但我发现的只是标准数组示例.

I've been searching the difference between Select and SelectMany but I haven't been able to find a suitable answer. I need to learn the difference when using LINQ To SQL but all I've found are standard array examples.

谁能提供一个 LINQ To SQL 示例?

Can someone provide a LINQ To SQL example?

推荐答案

SelectMany 扁平化返回列表列表的查询.例如

SelectMany flattens queries that return lists of lists. For example

public class PhoneNumber
{
    public string Number { get; set; }
}

public class Person
{
    public IEnumerable<PhoneNumber> PhoneNumbers { get; set; }
    public string Name { get; set; }
}

IEnumerable<Person> people = new List<Person>();

// Select gets a list of lists of phone numbers
IEnumerable<IEnumerable<PhoneNumber>> phoneLists = people.Select(p => p.PhoneNumbers);

// SelectMany flattens it to just a list of phone numbers.
IEnumerable<PhoneNumber> phoneNumbers = people.SelectMany(p => p.PhoneNumbers);

// And to include data from the parent in the result: 
// pass an expression to the second parameter (resultSelector) in the overload:
var directory = people
   .SelectMany(p => p.PhoneNumbers,
               (parent, child) => new { parent.Name, child.Number });

.NET Fiddle 现场演示

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