Using LINQ, select list of objects inside another list of objects

问题

public class ClassA
{
     public string MyString {get; set;}
}

public class ClassB
{
     public List<ClassA> MyObjects {get; set;}
}

List<ClassB> classBList = new List<ClassB>();
var results = (from i in classBList select i.MyObjects).Distinct();

I want a distinct list of all the ClassA objects in the classBList. How do I go about this using LINQ? I'm thinking about a nested query, but couldn't quite figure it out. Any help is very appreciated.

回答1:

You're trying to select multiple result objects for each ClassB object in the original list.

Therefore, you're looking for the SelectMany extension method:

var results = classBList.SelectMany(b => b.MyObjects).Distinct();

If you want to use query expressions, you'll need to use two from clauses:

var results = (from b in classBList from a in b.MyObjects select a).Distinct();

回答2:

You want to use IEnumerable.SelectMany() Extension Method to flatten the hierarchy:

var result = classBList.SelectMany(b => b.MyObjects).Distinct();

来源：https://stackoverflow.com/questions/3934583/using-linq-select-list-of-objects-inside-another-list-of-objects