Linq选择IList

Question

    List<MyParentClass> parents = new List<MyParentClass>();
    var parent1 = new MyParentClass("parent1");
    var parent2 = new MyParentClass("parent2");
    parents.Add(parent1);
    parents.Add(parent2);
    var child1 = new MyChildClass("child1");
    parent1.children.Add(child1);
    var child2 = new MyChildClass("child2");
    var child3 = new MyChildClass("child3");
    parent2.children.Add(child2);
    parent2.children.Add(child3);
    var foo = from p in parents
              select from c in p.children
                     select c;
    Assert.IsNotNull(foo);
    Assert.AreEqual(3, foo.Count());

NUnit.Framework.AssertionException: 
    expected: <3>
     but was: <2>

我想我正在回归IList，但我期待这三个孩子。我怎么做到的？

Answer 1

我对查询语法并不过分自信，但我认为这会使子列表变得扁平化：

var foo = from p in parents
          from c in p.children
          select c;

使用扩展方法语法，它看起来像这样：

var foo = parents.SelectMany(p => p.children);

Answer 2

您实际上正在返回IEnumerable＆lt; IEnumerable＆lt; MyChildClass＆gt;＆gt;。为了得到一个简单的IEnumerable＆lt; MyChildClass＆gt;你可以拨打以下电话

var bar = foo.SelectMany(x => x);