TypeError：undefined不是函数-Node.js＆MongoDB

Question

由于某种原因，找不到在我的光标对象上调用的函数。 这是我的代码：

var db = req.db;
var goalscollection = db.get('goalscollection');
var collection = db.get('hoursburnedcollection');

var cursor = collection.find({goal: selectedgoal}, console.log);  
// the line above prints the correct cursor object

var doc = cursor.hasNext() ? cursor.next() : null;  //line 51
// the line above gives an error

这是错误：

TypeError: undefined is not a function
at /Users/chrispark/Projects/LifeTool/node/routes/index.js:51:27
at Layer.handle [as handle_request] (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/layer.js:95:5)
at next (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/route.js:131:13)
at Route.dispatch (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/route.js:112:3)
at Layer.handle [as handle_request] (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/layer.js:95:5)
at /Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/index.js:277:22
at Function.process_params (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/index.js:330:12)
at next (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/index.js:271:10)
at Function.handle (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/index.js:176:3)
at router (/Users/chrispark/Projects/LifeTool/node/node_modules/express/lib/router/index.js:46:12)

有什么我想念的吗？ 提前致谢。

Answer 1

myCursor来自哪里？

使用cursor而不是myCursor ：

var doc = cursor.hasNext() ? cursor.next() : null;  //line 51

Answer 2

如果提供了find的回调函数，则游标将仅提供给回调，而不会返回。 因此，删除console.log参数，您将获得光标。

此外， next不返回下一个文档，而是通过异步回调将其提供回调用方。

var cursor = collection.find({goal: selectedgoal});
if (cursor.hasNext()) {
    cursor.next(function(err, doc) {
        console.log(doc);
    });
}

Answer 3

您确定错误行号吗？

我会说错误是从这些行来的：

var goalscollection = db.get('goalscollection');
var collection = db.get('hoursburnedcollection');

我找不到任何方法get的驱动程序API。 应该是db.collection() ：

var goalscollection = db.collection('goalscollection');
var collection = db.collection('hoursburnedcollection');