C ++ - 在STL向量中操作对象？(C++ - manipulating objects in a STL vector?)

 您正在寻找的功能是Promise链接 ，它允许您构建一系列承诺，每个承诺取决于前一个值的结果。 将此应用于您的代码，您将获得以下内容： 
 
 
 
 
 
  
exports.getArticleData = function(req, done) {
  pool.getConnection(function(error, connection) {
    if (error) throw error;

    // Inital query
    return connection.query(
        `SELECT article_id, title, is_listicle_article, FROM com_magazine_articles AS article WHERE article_id = ${req
            .params.articleId}`
    ).then((rows) => {
    
       return Promise.all(rows.map((article) => {
          if (article.is_listicle_article) {
            return connection.query(
                `SELECT * FROM com_magazine_article_listicles WHERE article_id = ${req.params
                    .articleId}`
             );
          } else {
             return Promise.resolve(null);
          }
       }));
    }).then((res) => {
     connection.release();
     done(res.filter(function(i){ return i != null; }));
    })

    // This query should only be excuted if is_listicle_article = true
    

    // More queries depending on the result of the first one
    // ....
    // ....

    // Callback with the data object
    connection.release();
  });
};
 
 
 
 
 
 显然，因为我没有你的所有代码，我无法验证这个例子，但这应该大致是你正在寻找的功能。 也就是说，我认为在您的示例代码中应该注意一些错误： 
 
 
 
 connection.query()返回一个promise（也就是说不需要回调函数）。 使用此功能有利于您 - 它将使您的代码更漂亮。 
 
 
 connection.query()返回行数组，而不是单个值。 您似乎在示例代码中忽略了这一点。 
 
 
 尝试在使用promises时不将内容保存到变量中，这是没有必要的。 要解决这个问题，请阅读Promise API（Promise.resolve（），Promise.reject（），Promise.any（），Promise.catch（），Promise.all（））等。 
 
 
 看起来这些SQL查询很容易组合成一个查询。 这将比执行两个操作更有效。 不确定您希望使用的其余查询是否属于这种情况，但绝对需要注意。 
 

The functionality you are looking for is Promise chaining, it allows you to construct a sequence of promises, each depending on the result of the previous value. Applying this to your code, you would get something like this:
 
 
 
 
 
  
exports.getArticleData = function(req, done) {
  pool.getConnection(function(error, connection) {
    if (error) throw error;

    // Inital query
    return connection.query(
        `SELECT article_id, title, is_listicle_article, FROM com_magazine_articles AS article WHERE article_id = ${req
            .params.articleId}`
    ).then((rows) => {
    
       return Promise.all(rows.map((article) => {
          if (article.is_listicle_article) {
            return connection.query(
                `SELECT * FROM com_magazine_article_listicles WHERE article_id = ${req.params
                    .articleId}`
             );
          } else {
             return Promise.resolve(null);
          }
       }));
    }).then((res) => {
     connection.release();
     done(res.filter(function(i){ return i != null; }));
    })

    // This query should only be excuted if is_listicle_article = true
    

    // More queries depending on the result of the first one
    // ....
    // ....

    // Callback with the data object
    connection.release();
  });
};
 
 
 
 
 
Obviously since I don't have all of your code, I couldn't verify this example, but this should be roughly the functionality you are looking for. That said, I think there were a couple of mistakes you should watch out for in your example code:
 
 
 
connection.query() returns a promise (aka doesn't need a callback function). Use this functionality to your advantage- it will make your code prettier.
 
 
connection.query() returns an array of rows, not a single value. You seemed to ignore this in your example code.
 
 
Try not to save things into a variable when using promises, it isn't necessary. To remedy this, read more into the Promise API (Promise.resolve(), Promise.reject(), Promise.any(), Promise.catch(), Promise.all()) etc.
 
 
It seems like these SQL queries could easily be combined into a single query. This will be way more efficient that performing two operations. Not sure if this is the case with the remaining queries you wish to use, but definitely something to look out for.