c# - 在 C# 中优化算法和/或结构

Question

我正在开发一个应用程序，您可以在其中订阅时事通讯并选择要订阅的类别。有两组不同的类别:城市和类别。

在发送电子邮件(这是一个预定的尝试)时，我必须在发送电子邮件之前查看订阅者订阅了哪些城市和哪些类别。也就是说，如果我订阅了“伦敦”和“曼彻斯特”作为我选择的城市，并选择了“食品”、“布料”和“电子产品”作为我的类别，我将只会收到与这些相关的时事通讯。

结构如下:

在 Umbraco CMS 中的每个 newsitem 上都有一个以逗号分隔的城市和类别字符串(实际上，它们存储为节点 ID，因为城市和类别也是 Umbraco 中的节点)当我订阅一个或多个城市和一个或多个类别时，我将城市和类别 nodeids 存储在数据库中的自定义表中。我的关系映射如下所示:

整个结构如下所示:

对我来说，这似乎是两组 1 - 1..* 关系(一个订阅者订阅一个或多个城市，一个订阅者订阅一个或多个类别)

要查找向哪个订阅者发送哪些电子邮件，我的代码如下所示:

private bool shouldBeAdded = false;

// Dictionary containing the subscribers e-mail address and a list of news nodes which should be sent
Dictionary<string, List<Node>> result = new Dictionary<string, List<Node>>();

foreach(var subscriber in subscribers)
{
    // List of Umbraco CMS nodes to store which nodes the html should come from
    List<Node> nodesToSend = new List<Node> nodesToSend();

    // Loop through the news
    foreach(var newsItem in news)
    {
        // The news item has a comma-separated string of related cities
        foreach (string cityNodeId in newsItem.GetProperty("cities").Value.Split(','))
        {
            // Check if the subscriber has subscribed to the city
            if(subscriber.CityNodeIds.Contains(Convert.ToInt32(cityNodeId)))
            {
                 shouldBeAdded = true;
            }
        }

        // The news item has a comma-separated string of related categories
        foreach (string categoryNodeId in newsItem.GetProperty("categories").Value.Split(','))
        {
            // Check if the subscriber has subscribed to the category
            if(subscriber.CategoryNodeIds.Contains(Convert.ToInt32(categoryNodeId)))
            {
                shouldBeAdded = true;
            }
        }
    }

    // Store in list
    if (shouldBeAdded)
    {
        nodesToSend.Add(newsItem);
    }

    // Add it to the dictionary
    if (nodesToSend.Count > 0)
    {
        result.Add(subscriber.Email, nodesToSend);
    }
}

// Ensure that we process the request only if there are any subscribers to send mails to
if (result.Count > 0)
{
    foreach (var res in result)
    {
        // Finally, create/merge the markup for the newsletter and send it as an email.
    } 
}

虽然这可行，但我有点担心达到一定数量的订阅者时的性能，因为我们进入了三个嵌套的 foreach 循环。另外，请记住我的老老师们的教导:“对于每个 for 循环，都有一个更好的结构”

那么，我想听听您对上述解决方案的看法，对于给定的结构，这里有什么可以改进的地方吗？随着时间的推移，它会导致性能问题吗？

非常感谢任何帮助/提示! :-)

提前致谢。

解决方案

因此，经过几个小时的调试和摸索，我终于想出了一些可行的方法(最初，它看起来像我的原始代码有效，但实际上没有)

遗憾的是，我无法让它与我尝试过的任何 LINQ 查询一起使用，所以我回到了“ol'school' 迭代方式；-)最终算法如下所示:

private bool shouldBeAdded = false;

// Dictionary containing the subscribers e-mail address and a list of news nodes which should be sent
Dictionary<string, List<Node>> result = new Dictionary<string, List<Node>>();

foreach(var subscriber in subscribers)
{
    // List of Umbraco CMS nodes to store which nodes the html should come from
    List<Node> nodesToSend = new List<Node> nodesToSend();

    // Loop through the news
    foreach(var newsItem in news)
    {
         foreach (string cityNodeId in newsItem.GetProperty("cities").Value.Split(','))
         {
             // Check if the subscriber has subscribed to the city
             if (subscriber.CityNodeIds.Contains(Convert.ToInt32(cityNodeId)))
             {
                 // If a city matches, we have a base case
                 nodesToSend.Add(newsItem);
             }
         }

         foreach (string categoryNodeId in newsItem.GetProperty("categories").Value.Split(','))
         {
             // Check if the subscriber has subscribed to the category
             if (subscriber.CategoryNodeIds.Contains(Convert.ToInt32(categoryNodeId)))
             {
                 shouldBeAdded = true;

                 // News item matched and will be sent. Stop the loop.
                 break;
             }
             else
             {
                 shouldBeAdded = false;
             }
         }

         if (!shouldBeAdded)
         {
             // The news item did not match both a city and a category and should not be sent
             nodesToSend.Remove(newsItem);
         }
    }

    if (nodesToSend.Count > 0)
    {
        result.Add(subscriber.Email, nodesToSend);
    }  
}

// Ensure that we process the request only if there are any subscribers to send mails to
if (result.Count > 0)
{
    foreach (var res in result)
    { 
        // StringBuilder to build markup for newsletter
        StringBuilder sb = new StringBuilder();

        // Build markup
        foreach (var newsItem in res.Value)
        {
            // build the markup here
        }

        // Email logic here
    }
}

Answer 1

首先，您可以在shouldBeAdde = true 时中断 内部foreach。

您也可以使用 LINQ，但我不确定它是否会更快(但您可以使用 .AsParallel 使其轻松实现多线程):

var nodesToSend = from n in news
                 where n.GetProperties("cities").Value.Split(',')
                     .Any(c => subscriber.CityNodeIds.Contains(Convert.ToInt32(c)) &&
                 n.GetProperties("categories").Value.Split(',')
                     .Any(c => subscriber.CategoryNodeIds.Contains(Convert.ToInt32(c))
                 select n;

完整的想法将归结为(包括并行):

Dictionary<string, IEnumerable<Node>> result = new Dictionary<string, IEnumerable<Node>>();
foreach(var subscriber in subscribers)
{
    var nodesToSend = from n in news.AsParallel()
        where n.GetProperties("cities").Value.Split(',')
                .Any(c => subscriber.CityNodeIds.Contains(Convert.ToInt32(c)) &&
            n.GetProperties("categories").Value.Split(',')
                .Any(c => subscriber.CategoryNodeIds.Contains(Convert.ToInt32(c))
        select n;

    if (nodesToSend.Count > 0)
        result.Add(subscriber.Email, nodesToSend);
}

if (result.Count > 0)
{
    foreach (var res in result)
    {
        // Finally, create/merge the markup for the newsletter and send it as an email.
    } 
}