Linq扩展方法，如何在集合递归中查找子项 [英] Linq extension method, how to find child in collection recursive

问题描述

我已经熟悉Linq，但是对扩展方法了解甚少，我希望有人可以帮助我.

I'm already familiar with Linq but have little understanding of extension methods I'm hoping someone can help me out.

所以我有这个分层的集合伪代码，即:

So I have this hierarchical collection pseudo code ie:

class Product
  prop name
  prop type
  prop id
  prop List<Product> children

我有一个产品列表，列出产品.

And I have a list of products List products.

我是否可以通过扩展方法通过 id 在此系列中查找产品?换句话说，我在层次结构中的某处需要一个项目.

Is there any way I can look for product in this collection by the id with a extension method ? In other words I need one item somewhere within the hierarchy.

推荐答案

这里是一种通用解决方案，一旦找到匹配项，它将缩短对层次结构的遍历.

Here is a generic solution that will short-circuit traversal of the hierarchy once a match is found.

public static class MyExtensions
{
    public static T FirstOrDefaultFromMany<T>(
        this IEnumerable<T> source, Func<T, IEnumerable<T>> childrenSelector,
        Predicate<T> condition)
    {
        // return default if no items
        if(source == null || !source.Any()) return default(T);

        // return result if found and stop traversing hierarchy
        var attempt = source.FirstOrDefault(t => condition(t));
        if(!Equals(attempt,default(T))) return attempt;

        // recursively call this function on lower levels of the
        // hierarchy until a match is found or the hierarchy is exhausted
        return source.SelectMany(childrenSelector)
            .FirstOrDefaultFromMany(childrenSelector, condition);
    }
}

要在您的情况下使用它:

To use it in your case:

var matchingProduct = products.FirstOrDefaultFromMany(p => p.children, p => p.Id == 27);

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