Mongodb查询中的未定义值(Undefined value in Mongodb query)

 我想通过Mongodb查询从服务器端向客户端发送json数据。 我已经处理了我对数据库和连接内容的查询。 
 
function mongoDbHandleLoad()
{
    MongoClient.connect(MongoDBURL, function(err, db)
    {

        /*
         db.createCollection('user', {strict:true},  function(err, collection) {
         if(err)
         return console.dir(err);
         });
         */

        db.collection('user', function(err, collection) {
            if(!err)
            {
                collection.find().toArray(function(err, docs) {
                    if(!err)
                    {
                        var intCount = docs.length;
                        var responseBody;
                        if(intCount > 0)
                        {
                            console.log("responseBody in mongodb handle", JSON.stringify(docs[docs.length-1]));
                            return JSON.stringify(docs[docs.length-1]);
                        }
                    }
                });
            }
        });
    });

    /*
        if(docs != null)
        {
            console.log("docs", docs);
            return resParam.json(docs); //return the first document found
        }
    */
}
 
 我使用此代码段成功发送了测试json数据。 
 
if(str.localeCompare(controlPathDatabaseLoad) == 0)
{
    console.log("controlPathDatabaseLoad");
    mongoDbHandleLoad();
    res.setHeader('Content-Type', 'application/json');
    res.writeHead(res.statusCode);
    res.write(JSON.stringify(testJSON));
    res.end();
}
 
 当我想在mongoDbHandleLoad（）函数内发送数据“JSON.stringify（docs [docs.length-1]）”时，即使我用回调改变了函数，我也无法正常工作。 我从mongoDbHandleLoad函数中获取未定义的值。 如何修改代码以获取“JSON.stringify（docs [docs.length-1]）”的正确值。 
 
 提前致谢， 

I want to send a json data via Mongodb query from the server side to client side. I have handled my query of database and connection stuff as you can see.
 
function mongoDbHandleLoad()
{
    MongoClient.connect(MongoDBURL, function(err, db)
    {

        /*
         db.createCollection('user', {strict:true},  function(err, collection) {
         if(err)
         return console.dir(err);
         });
         */

        db.collection('user', function(err, collection) {
            if(!err)
            {
                collection.find().toArray(function(err, docs) {
                    if(!err)
                    {
                        var intCount = docs.length;
                        var responseBody;
                        if(intCount > 0)
                        {
                            console.log("responseBody in mongodb handle", JSON.stringify(docs[docs.length-1]));
                            return JSON.stringify(docs[docs.length-1]);
                        }
                    }
                });
            }
        });
    });

    /*
        if(docs != null)
        {
            console.log("docs", docs);
            return resParam.json(docs); //return the first document found
        }
    */
}
 
And I send a test json data successfully with this code snippet. 
 
if(str.localeCompare(controlPathDatabaseLoad) == 0)
{
    console.log("controlPathDatabaseLoad");
    mongoDbHandleLoad();
    res.setHeader('Content-Type', 'application/json');
    res.writeHead(res.statusCode);
    res.write(JSON.stringify(testJSON));
    res.end();
}
 
When I wanted to send the data "JSON.stringify(docs[docs.length-1])" inside of mongoDbHandleLoad() function, even though I changed function with callback, I couldn't do properly. I take undefined value from mongoDbHandleLoad function. How can I modify to code to take proper value of "JSON.stringify(docs[docs.length-1])".
 
Thanks in advance,

原文：https://stackoverflow.com/questions/42754949