我相信这会做你想要的。 在递归调用函数之前，您已声明了该函数。 
 
// Declare the function so that it can be referenced from within
// the function definition.
Func<Node, object> convert = null;

// Define the function.
// Note the recursive call when setting the 'Children' property.
convert = n => new 
{
    id = n.AssociatedObject.ID,
    name = n.AssociatedObject.Name,
    children = n.Children.Select(convert)
};

// Convert the list of nodes to a list of the new type.
var jsonTree = 
    nodes
    .Select(convert)
    .ToList();
 
 更新 
 
 通过在C＃7中引入本地函数，您现在可以在函数中定义函数，就像通常定义函数和递归一样。 
 
// Declare and define the function as you normally would.
object convert (Node node)
{
    id = n.AssociatedObject.ID,
    name = n.AssociatedObject.Name,
    children = n.Children.Select(convert);
};

// Convert the list of nodes to a list of the new type.
var jsonTree = 
    nodes
    .Select(convert)
    .ToList();

I believe this will do what you want. Before you can call a function recursively you have declare the function.
 
// Declare the function so that it can be referenced from within
// the function definition.
Func<Node, object> convert = null;

// Define the function.
// Note the recursive call when setting the 'Children' property.
convert = n => new 
{
    id = n.AssociatedObject.ID,
    name = n.AssociatedObject.Name,
    children = n.Children.Select(convert)
};

// Convert the list of nodes to a list of the new type.
var jsonTree = 
    nodes
    .Select(convert)
    .ToList();
 
Update
 
With the introduction of local functions in C# 7 you can now define a function within a function as you would normally define a function and recursion simply works.
 
// Declare and define the function as you normally would.
object convert (Node node)
{
    id = n.AssociatedObject.ID,
    name = n.AssociatedObject.Name,
    children = n.Children.Select(convert);
};

// Convert the list of nodes to a list of the new type.
var jsonTree = 
    nodes
    .Select(convert)
    .ToList();